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Am J Physiol Endocrinol Metab 290: E1162-E1171, 2006. First published January 3, 2006; doi:10.1152/ajpendo.00469.2005
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Stimulatory effect of PYY-(3–36) on gonadotropin secretion is potentiated in fasted rats

L. Pinilla,* R. Fernández-Fernández,* E. Vigo, V. M. Navarro, J. Roa, J. M. Castellano, R. Pineda, M. Tena-Sempere, and E. Aguilar

Department of Cell Biology, Physiology and Immunology, University of Córdoba, Cordoba, Spain

Submitted 26 September 2005 ; accepted in final form 25 December 2005


   ABSTRACT
TOP
 ABSTRACT
MATERIAL AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Development and normal function of the reproductive axis requires a precise degree of body energy stores. Polypeptide YY-(3–36) [PYY-(3–36)] is a gastrointestinal secreted molecule recently shown to be involved in the control of food intake with agonistic activity on neuropeptide Y (NPY) receptor subtypes Y2 and Y5. Notably, PYY-(3–36) has been recently demonstrated as putative regulator of gonadotropin secretion in the rat. However, the "reproductive" facet of this factor remains to be fully elucidated. In this context, we report herein our analyses of the influence of the nutritional status on the effects of PYY-(3–36) upon GnRH and gonadotropin secretion. The major findings of our study are 1) the stimulatory effect of central administration of PYY-(3–36) on LH secretion was significantly enhanced after fasting and blocked by a GnRH antagonist; 2) besides central effects, PYY-(3–36) elicited LH and FSH secretion directly at the pituitary level, a response that is also augmented by fasting; 3) PYY-(3–36) inhibited GnRH secretion by hypothalamic fragments from male rats fed ad libitum, whereas a significant stimulatory effect was observed after fasting; and 4) the increase in the gonadotropin responsiveness to PYY-(3–36) in fasting was not associated with changes in the expression of Y2 and Y5 receptor genes at hypothalamus and/or pituitary. In conclusion, our study extends our previous observations suggesting a relevant, mostly stimulatory, role of PYY-(3–36) in the control of gonadotropin secretion. Strikingly, such an effect was significantly enhanced by fasting. Considering the proposed decrease in PYY-(3–36) levels after fasting, the possibility that reduced PYY-(3–36) secretion might contribute to defective function of the gonadotropic axis after food deprivation merits further investigation.

polypeptide YY-(3–36); gonadotropin-releasing hormone; luteinizing hormone; follicle-stimulating hormone; fasting; pituitary

ALTHOUGH IT IS KNOWN that conditions of negative energy balance are frequently linked to lack of puberty onset and reproductive failure, at the moment the mechanisms involved in fitting the reproductive function to body energy stores remain incompletely defined. Compelling evidence has recently demonstrated that central and peripheral endocrine signals governing energy homeostasis, such as the adipocyte-derived hormone leptin, the stomach-derived hormone ghrelin, orexins, and neuropeptide Y (NPY), are also involved in the control of reproductive function by acting at different levels of hypothalamic-pituitary-gonadal axis.

In this context, it has been demonstrated that NPY, a member of the pancreatic polypeptide family (54), is involved in the control of food intake, reproductive function, and pituitary secretion (26, 27, 30, 33). In rats, central administration of NPY advances puberty (43), whereas immunoneutralization of NPY reduced the magnitude of the LH surge during the afternoon of first proestrus (42). A facilitatory role of NPY on the onset of puberty has been also reported in the female rhesus monkey (23) and in chicks (18). Secretion of NPY to portal vasculature is increased on the afternoon of proestrus and serves to amplify the actions of gonadotropin-releasing hormone (GnRH) in initiating the preovulatory surges of LH and probably FSH (53). Acute intracerebroventricular (icv) administration of NPY stimulated LH release in ovariectomized rats primed with ovarian steroids (4). These excitatory effects have been shown to be the consequence of an increase in secretion and effectiveness of GnRH (5, 14). In contrast, chronic treatment with the peptide decreased FSH, LH, and testosterone secretion (47, 9). NPY hypersecretion was observed in genetically obese and sterile hyperphagic rodents, which demonstrated the inverse relationship between chronic NPY secretion and reproductive function (15).

NPY exerts its actions throughout at least five receptor subtypes (16). Development of selective agonists/antagonists for different receptors and utilization of knockout animals have improved our understanding of the role of different receptor subtypes for NPY in the control of reproductive axis, although at the moment the characterization of the specific role of the different receptor subtypes is scarce. Recent experiments have shown that the NPY Y1 receptor inhibits the gonadotrope axis (22) and that its blockade accelerates the onset of puberty (49). In addition, NPY Y4 receptors have been involved in the NPY effects on LH release (25), and experimental evidence suggests that the inhibition of LH secretion exerted by central administration of NPY in the rats is predominantly mediated by Y5 receptors (51).

Polypeptide YY-(3–36) [PYY-(3–36)], a hormone from gastrointestinal origin structurally related to NPY and an agonist of receptor subtypes Y2 and Y5 (36), has been recently proposed as a putative anorexigenic signal involved in the control of food intake (3, 24, 50). Conflicting results on the repeatability of the effects of PYY-(3–36) in terms of body weight control have been also published (13, 60). Although the potential role of PYY-(3–36) in fitting the reproductive function to body energy stores is still poorly characterized, recent data suggested its involvement in the control of reproductive axis. Thus, in addition to the reported presence of PYY-(3–36) in placenta (62), recent data from our laboratory indicated that PYY-(3–36) stimulates in vitro FSH and LH secretion by pituitaries from prepubertal female and male rats and inhibited in vitro GnRH secretion selectively in males (17). In addition, infusion of PYY-(3–36) into the lateral ventricle rapidly inhibited estrous behavior in ovariectomized steroid-primed hamsters (35) and decreased LH secretion in prepubertal male rats (17).

It is well known that fasting strongly inhibits gonadotropin secretion (6, 7). Considering that PYY-(3–36) stimulates in vitro gonadotropin secretion (17) and that PYY-(3–36) secretion is depressed during fasting (59), we hypothesized that decreased secretion of PYY-(3–36) during food deprivation might be involved in the suppressive effect on pituitary-gonadal function. To test this hypothesis, we have analyzed the in vivo and in vitro effects of PYY-(3–36) on GnRH and gonadotropin secretion after fasting.


   MATERIAL AND METHODS
TOP
 ABSTRACT
 MATERIAL AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals and drugs. Wistar rats born in our laboratory were kept under controlled conditions of light (12:12-h light-dark cycle, lights on at 0700) and temperature (22°C) with free access to pelleted food (Pacsa Sanders, Seville, Spain) and tap water. Experiments were carried out in adult (90–100 days) animals. Vaginal smears of adult females were monitored daily, and only those rats exhibiting two or more regular cycles were used. PYY-(3–36) was purchased from Bachem (Barcelona, Spain). GnRH antagonist (GnRH-ANT) was ORG.30276 (Ac-D-p-Cl-Phe-D-p-Cl-Phe-D-Trp-Ser-Tyr-D-Arg-Leu-Arg-Prol-D-Ala-NH2 CH3·COOH) and was purchased from Organon International (Oss, The Netherlands). For in vivo experiments, PYY-(3–36) and GnRH-ANT were dissolved in saline immediately before use, whereas for in vitro experiments PYY-(3–36) was dissolved in Dulbecco’s Modified Eagle’s Medium (DMEM; BioWhittaker, Verviers, Belgium) immediately before use. Doses of drugs were selected on the basis of previous studies (17, 57).

Experimental designs. Experimental procedures were approved by the Córdoba University Ethics Committee for Animal Experimentation and were conducted in accordance with the European Union norms for care and use of experimental animals. The number of animals per experimental group is provided in the figure legends. Experiments were carried out between 1000 and 1200. Special caution was taken to avoid any stressing influences on the experimental animals (all the animals were handled daily for 1 wk before the experiment and humanely killed by the same person, and the different drugs were injected at random).

In vivo experiments. In the first set of experiments, and to characterize the possible effects of fasting in the effects of PYY-(3–36) on gonadotropin secretion, adult (90 days) males were submitted to a 4-day period of absolute restriction of food. Control animals were fed ad libitum. The animals were injected icv with 3 nmol/rat of PYY-(3–36) or vehicle. The procedure of icv injection was as previously described (48). Briefly, animals were implanted, 2 days before PYY-(3–36) administration, with icv cannulas under light ether anesthesia. To allow delivery of PYY-(3–36) into the lateral cerebral ventricle, the cannulas were lowered to a depth of 4 mm beneath the surface of the skull; the insert point was 1 mm posterior and 1.2 mm lateral to bregma. Animals were humanely killed 15, 30, or 60 min after injection, and trunk blood samples were collected.

To analyze whether the stimulatory effect of PYY-(3–36) on gonadotropin secretion was exerted throughout an increase in GnRH release, adult male rats submitted to a 4-day period of absolute restriction of food and corresponding control groups were subcutaneously injected with GnRH-ANT (5 mg/kg per rat) 48 and 24 h before icv administration of PYY-(3–36) (3 nmol per rat). Blood samples were obtained by decapitation 15, 30, or 60 min after PYY-(3–36) injection.

In vitro experiments. Adult cyclic female and male rats were submitted to a 4-day period of absolute restriction of food. Control animals received food ad libitum. Thereafter, the animals were humanely killed (the control females being in metestrus), and hypothalami and pituitaries were removed to analyze the effects of PYY-(3–36) on GnRH and gonadotropin secretion. Hypothalamic samples were dissected out, as described in detail elsewhere (45), by a horizontal cut of ~2 mm depth with the following limits: 1 mm anteriorly from the optic chiasma, the posterior border of mamillary bodies, and the hypothalamic fisures. Hypothalami were placed in scintillation vials and incubated in 500 µl of DMEM in a Dubnoff shaker incubator under an atmosphere of 95% O2-5% CO2 at 37.5°C. After a 30-min preincubation, the medium was removed, and hypothalamic fragments were challenged for 45 min with PYY-(3–36) (10–6 M) or DMEM alone. At the end of the incubation period, medium samples were boiled for 30 min to inactivate endogenous protease activity and stored at –80°C until used for GnRH determinations. Anterior pituitaries were halved and placed in scintillation vials. After 1 h of preincubation, the medium was replaced by fresh medium alone or medium containing PYY-(3–36) (10–8 and 10–6 M). Samples were collected at 60 and 120 min of the incubation period for LH and FSH determinations.

Finally, to analyze whether the increase in the responsiveness to gonadotropin at PYY-(3–36) in fasted rats could be mediated by an increase in the NPY Y2 and Y5 receptor subtypes, adult males were submitted to a 4-day period of absolute restriction of food. Control animals were fed ab libitum. Thereafter, animals (9–12 animals/group) were humanely killed by decapitation, and pituitary and hypothalamus were immediately dissected (as described above), snap-frozen in liquid nitrogen, and stored at –80°C until use for RNA isolation and analysis.

LH, FSH, GnRH, and leptin measurements by specific RIAs. After centrifugation (1,600 g at 4°C for 20 min), serum was collected, frozen, and stored at –20°C until use. The concentrations of LH and FSH were measured in 5–50 µl by a double-antibody method using RIA kits supplied by the National Institute of Diabetes and Digestive and Kidney Diseases (Bethesda, MD). Rat-LH-I-10 and FSH-I-9 were labeled with 125I by the chloramine T method, and hormone concentrations were expressed using a reference preparation LH-RP3 and FSH-RP2 as standard. Intra- and interassay variations were, respectively, 8 and 10% for LH and 6 and 9% for FSH. The sensitivities of the assay were 75 and 400 pg/ml for LH and FSH, respectively. In addition, GnRH concentrations in the incubation media from hypothalamic explants were measured in 100-µl aliquots by use of a commercial RIA kit purchased from Peninsula Laboratories (Bachem, San Carlos, CA), following the instructions of the manufacturer. The sensitivity of the assay was 1 pg/tube. All samples of each experiment were measured in the same assay. Serum leptin concentrations were measured in control and fasted rats with a commercial kit from Linco Research (St. Charles, MO), following the instructions of the manufacturer. The sensitivity of the assay was 0.05 ng/tube, and the intra-assay coefficient of variation was <5%.

RNA analysis by RT-PCR. Hypothalamic and pituitary expression of NPY Y2 and NPY-Y5 receptor mRNAs was assessed by semiquantitative RT-PCR. Total mRNA was isolated from tissue samples by use of the single-step, acid guanidinum thiocyanate-phenol-chloroform extraction method followed by DNase I treatment (12). For amplification of the target genes, the following primer pairs were used: NPY Y2 sense (nt 375–398, 5'-GGT GCC CTA TGC CCA GGG TCT GGC-3') and NPY Y2 antisense (nt 530–509, 5'-GCG CTG ACA CCC CAC GCC AGG C-3') for amplification of a 156-bp fragment of rat NPY Y2 receptor cDNA; and NPY Y5 sense (nt 131–153, 5'-GGT CCT GCT CCT GCC GCC ACC GC-3') and NPY Y5 antisense (nt 274–253, 5'-CTT GTT AAA ATG CTC CTC AAG C-3') for amplification of a 144-bp fragment of rat NPY Y5 receptor cDNA. These oligo primers were synthesized according to the published rat cDNA sequences of NPY Y2 and NPY Y5 (GenBank acc. nos. NM-023968 and NM-012869, respectively). In addition, to provide an appropriate internal control, parallel amplification of a 241-bp fragment of S11 ribosomal protein mRNA was carried out in each sample, using the primer pair S11 sense (nt 11/32, 5'-CAT TCA GAC GGA GCG TG TTA C-3') and S11 antisense (nt 231/250, 5'-TGC ATC TTC ATC TTC GTC AC-3').

For amplifications of the targets, RT-PCR was run in two separate steps. Furthermore, to enable appropriate amplification in the exponential phase for each target, PCR amplification of specific signal and S11 ribosomal protein transcripts was carried out in separate reactions with different numbers of cycles (see below) but using similar amounts of the corresponding cDNA templates, generated in single RT reactions, as previously described (55, 58). Briefly, equal amounts of total RNA (2 µg) were heat denatured and reverse transcribed by incubation at 42°C for 90 min with 12.5 U of avian myeloblastosis virus (AMV) RT (Promega, Madison, WI), 20 U of ribonuclease inhibitor RNasin (Promega), 200 mM dNTP mixture, and 1 nM specific and internal control antisense primers in a final volume of 30 µl of 1x AMV-RT buffer. The reactions were terminated by heating at 97°C for 5 min and cooling on ice, followed by dilution of the RT cDNA samples with nuclease-free H2O (final volume, 60 µl). For semiquantitative PCR, 10 µl-aliquots of the cDNA samples (equivalent to 650 ng of total RNA input) were amplified in 50 µl of 1x PCR buffer in the presence of 2.5 U of Taq DNA polymerase (Promega), 200 nM dNTP mixture, and the appropriate primer pairs (1 nM of each primer). PCR reactions consisted of a first denaturing cycle at 97°C for 5 min followed by a variable number of cycles of amplification (n = 36 cycles for NPY Y2 and Y5; n = 26 cycles for RP-S11) defined by denaturation at 96°C for 1.5 min, annealing for 1.5 min, and extension at 72°C for 3 min. A final extension cycle of 72°C for 15 min was included. Annealing temperature was adjusted for each target: 58°C for NPY Y2 receptor and S11 and 61.5°C for NPY Y5 receptor. Different numbers of cycles were tested to optimize amplification in the exponential phase of PCR. On this basis, the numbers of PCR cycles indicated above were chosen for further semiquantitative analysis targets and RP-S11 internal control.

PCR-generated DNA fragments were resolved in Tris borate-buffered 1.5% agarose gels and visualized by ethidium bromide staining. Specificity of PCR products was confirmed by direct sequencing (Central Sequencing Service, University of Córdoba). Quantification of intensity of RT-PCR signals was carried out by densitometric scanning, and values of the specific targets were normalized to those of internal control to express arbitrary units of relative expression. In all assays, liquid controls and reactions without RT were included, yielding negative amplification.

Presentation of data and statistics. Values are expressed as means ± SE. When relevant, integrated LH and FSH secretory responses were calculated as the area under the curve (AUC), obtained following the trapezoidal rule, over the 60-min period after administration of PYY-(3–36). Differences between groups were analyzed using Student’s t-test or two-way ANOVA followed by a Student-Newman-Keuls multiple range test.


   RESULTS
TOP
 ABSTRACT
 MATERIAL AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Effects of PYY-(3–36) on in vivo gonadotropin secretion. In adult males, a 4-day period of absolute restriction of food induced a significant decrease in body weight (282 ± 10 vs. 325 ± 5 g in controls) and in serum LH and leptin concentrations (Table 1). Intracerebroventricular administration of PYY-(3–36) (3 nmol per rat) significantly stimulated LH and FSH secretion in controls fed ad libitum and in fasted animals (Table 1) without affecting serum leptin concentrations. Interestingly, the LH response in fasted animals was higher than in the control group, either when response was estimated by absolute LH levels reached after PYY-(3–36) administration or by the fold increase in serum LH concentrations (Table 1). To obtain information about the time course of the stimulatory effect of PYY-(3–36) on gonadotropin secretion, blood samples were obtained 15, 30, and 60 min after peptide administration in adult controls and fasted male rats. Results obtained showed that the stimulatory effect on gonadotropin secretion remain evident at least 60 min after icv administration of PYY-(3–36) (Fig. 1). Treatment with GnRH-ANT abolished completely the stimulatory effect of PYY-(3–36) on LH and FSH secretion in controls and fasted rats (Fig. 1).


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  		Table 1. Serum LH, FSH, and leptin concentrations in adult males either ad libitum or submitted to 4 days of absolute restriction of food (fasting), 15 min after icv administration of PYY-(3–36) (3 nmol per rat)

 

Figure 1
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  		Fig. 1. Serum concentrations of LH (top) and FSH (bottom) in male rats, either fed ad libitum or at fasting, which were injected sc with gonadotropin-releasing hormone antibody (GnRH-ANT; 5 mg/kg) or vehicle 48 and 24 h before icv injection with vehicle or 3 nmol per rat of polypeptide (P)YY-(3–36). Food deprivation was maintained for 4 days. Values are expressed as means ± SE (10–12 animals/group). **P ≤ 0.01 vehicle + PYY-(3–36) vs. other groups + PYY-(3–36) (ANOVA followed by Student-Newman-Keuls test). Insets: integrated gonadotropin secretory responses following central administration of PYY-(3–36) and peripheral administration of GnRH-ANT [calculated as area under the curve (AUC) during the 60-min study period] in control and fasted rats. Bars with different superscript letters were statistically different (ANOVA followed by Student-Newman-Keuls test).

 
Effects of PYY-(3–36) on in vitro GnRH secretion in adult male rats. PYY-(3–36) (10–6 M) significantly inhibited GnRH secretion by hypothalamic fragments from control males fed ad libitum (Fig. 2). Food deprivation for 4 days reduced, in the limits of statistical significance, basal GnRH secretion (11.07 ± 2.21 vs. 16.42 ± 1.40 pg per fragment). In contrast with the inhibitory effect in ad libitum control animals, PYY-(3–36) significantly stimulated GnRH by hypothalamic samples from fasted animals (Fig. 2).


Figure 2
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  		Fig. 2. GnRH released (pg per hypothalamus per 45 min) by hypothalami from adult male rats, either fed ad libitum or at fasting, incubated in the presence of PYY-(3–36) (10–6 M) or medium (DMEM) alone. Food deprivation was maintained for 4 days before incubation of hypothalami. Values are expressed as means ± SE (10–12 samples/group). **P ≤ 0.01 and *P ≤ 0.05 vs. corresponding control (DMEM) group (ANOVA followed by Student-Newman-Keuls test).

 
Effects of PYY-(3–36) on in vitro gonadotropin secretion. In males, in hemipituitaries from control rats fed ad libitum, 10–6 M PYY-(3–36) significantly increased LH secretion at 60 and 120 min of the incubation period, whereas the dose of 10–8 M increased LH secretion only at 120 min (Fig. 3). After a 4-day period of absolute food restriction, both doses of PYY-(3–36) significantly increased LH secretion at 60 and 120 min of incubation period, the responses being significantly greater than in control group (Fig. 3). FSH secretion was similarly stimulated at 60 min of the incubation period in controls fed ad libitum and in fasted rats by both doses of PYY-(3–36), and the effect disappeared at 120 min of the incubation period (Fig. 3).


Figure 3
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  		Fig. 3. Effects of PYY-(3–36) (10–8 and 10–6 M) on LH (top) and FSH (bottom) secreted by hemipituitaries obtained from adult controls fed ad libitum (open bars) or fasting males (hatched bars). Food deprivation was maintained for 4 days before incubation of hemipituitaries. Values are expressed as means ± SE (10–12 samples/group). **P ≤ 0.01 vs. hemipituitaries incubated in absence of PYY-(3–36); aP ≤ 0.01 vs. corresponding fed ad libitum control group (ANOVA followed by Student-Newman-Keuls test).

 
In females, in hemipituitaries from control metestrous females fed ad libitum, PYY-(3–36) was unable to stimulate LH or FSH secretion, except for a significant increase in LH observed at 60 min of the incubation period in presence of a higher dose of PYY-(3–36) (Fig. 4). However, after a 4-day period of absolute food restriction, LH and FSH secretion was significantly stimulated by both doses of PYY-(3–36) (Fig. 4).


Figure 4
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  		Fig. 4. Effects of PYY-(3–36) (10–8 and 10–6 M) on LH (top) and FSH (bottom) secreted by hemipituitaries obtained from adult controls fed ad libitum (open bars) or fasting female rats (hatched bars). Control females were studied in metestrus. Food deprivation was maintained for 4 days before incubation of hemipituitaries. Values are expressed as means ± SE (10 samples/group). **P ≤ 0.01 vs. hemipituitaries incubated in absence of PYY-(3–36); aP ≤ 0.01 vs. corresponding fed ad libitum control group (ANOVA followed by Student-Newman-Keuls test).

 
To compare the effectiveness of PYY-(3–36) in controls fed ad libitum and in fasted rats, results were expressed as changes over the concentrations measured in the absence of PYY-(3–36). Figure 5 clearly evidences that the overall response was greater in fasted animals than in ad libitum control animals.


Figure 5
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  		Fig. 5. Comparison between effects of PYY-(3–36) on LH (top) and FSH (bottom) secreted by hemipituitaries obtained from adult ad libitum-fed control (open bars) and fasting (hatched bars) male and female rats. Results are presented as changes over levels obtained in absence of PYY-(3–36). **P ≤ 0.01 vs. corresponding fed ad libitum control group (ANOVA followed by Student-Newman-Keuls test).

 
Hypothalamic and pituitary mRNA expression of NPY Y2 and Y5 receptors in fed and fasted rats. RT-PCR analysis using specific primer pairs demonstrated that the expression of the genes encoding NPY receptors Y2 and Y5 at the hypothalamus and pituitary of adult rats was similar in ad libitum control and fasted rats (Fig. 6).


Figure 6
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  		Fig. 6. Expression of genes encoding NPY receptors Y2 and Y5 at the hypothalamus (top) and pituitary (bottom) from adult male rats fed ad libitum (open bars) or fasting males (hatched bars). Food deprivation was maintained for 4 days before study. Representative images of ethidium bromide-stained gel electrophoresis of the specific amplicons are presented. Three independent samples from controls fed ad libitum (C1–C3) and fasting rats (F1–F3) are shown. Amplification of a fragment of ribosomal protein S11 mRNA served as internal control. Semiquantitative values of gene expression levels in the experimental groups are shown, which are means ± SE of ≥3 independent determinations. Negative controls were run in parallel with specific RT-PCR assays and yielded negative amplification (data not shown).

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIAL AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The relationship between energy balance, body weight, and reproductive function is well known after the pioneering works Frish and colleagues (20, 21). Different hormonal signals such as leptin, ghrelin, and orexins seem to be involved in the fine coordination between body weight and reproductive function (2, 52, 56).

The key signal in the regulation of reproductive function is the pulsatile secretion of GnRH, which controls gonadotropin release. GnRH release is primarily controlled by central and peripheral signals (28, 29, 41). NPY, secreted from hypothalamus to the hypothalamic-pituitary-portal system, was characterized as "a unique member of the family of gonadotropic releasing hormones" (19), due to their multiple effects on hypothalamic GnRH secretion and in the pituitary responsiveness to GnRH. Selective agonists and antagonists for the different NPY receptors and different knockout animals have been used to elucidate the role of different NPY receptors in the control of feeding behavior and reproductive function. Recently, it has been demonstrated that PYY-(3–36), agonist of NPY Y2 and Y5 receptors, is secreted from the gastrointestinal tract depending on the nutritional status of the animal. A regulatory loop involving this peptide has been proposed: after food intake, PYY-(3–36) is secreted and inhibits feeding behavior, whereas its release is depressed in underfeeding conditions (3, 59).

In previous experiments, we demonstrated the presence of NPY Y2 and Y5 receptor subtypes in hypothalamus and pituitary and the complex actions of PYY-(3–36) at the hypothalamic and pituitary level (17). PYY-(3–36) directly stimulated gonadotropin secretion by prepubertal pituitaries and significantly inhibited GnRH secretion by hypothalamic explants in males. The systemic and central administration of the peptide exerted changes in serum concentrations of gonadotropins, the effects being sexually dimorphic (17). The present studies extend and reinforce our previous hypothesis that PYY-(3–36) is involved in the control of gonadotropin secretion. Specifically, herein we have analyzed the effects of PYY-(3–36) in the control of gonadotropin and GnRH secretion during fasting.

Periods of chronic undernutrition, as well as short periods of fasting, have been shown to have an adverse impact on mammalian reproduction in various ways. Fasting suppresses GnRH release and, hence, pituitary LH, FSH, and testosterone secretion, which are reversed by pulsatile GnRH substitution (6, 7, 31, 61). The neural pathways that relay information on insufficient energy stores to GnRH neurons included many signals. Different neuropeptides and neurotransmitters [such as NPY, adrenaline via {alpha}2-adrenergic receptors, corticotropin-releasing hormone (CRH), leptin, ciliary neurotropic factor (CNTF), {gamma}-aminobutyric acid, and opioids] have been implicated in the effects of fasting on pituitary secretion (8, 32, 38, 39, 40, 44).

Acute administration of NPY stimulates GnRH/LH release (4, 5, 14), whereas continuous NPY receptor activation results in suppression of gonadotropin secretion (9, 15, 47), which explains that, in experimental conditions that upregulate NPY synthesis and release, such as diabetes, the reproductive function is also impaired (31). Acute and chronic food deprivation and undernutrition stimulate hypothalamic NPY synthesis, storage, and release in the hypothalamus (31, 46, 61). Consequently, fasting-induced upregulation of NPY secretion may diminish gonadotropin secretion. This hypothesis is sustained by the finding that counteracting the fasting-induced NPY upregulation experimentally with those naturally occurring compounds that inhibit the hypothalamic NPY system, such as CNTF, it is possible to attenuate the fasting-induced suppression of pituitary LH secretion (32). In summary, undernutrition induces an upregulation of the NPY system in the arcuate nucleus, which, in turn, suppresses GnRH and gonadotropin secretion.

In addition to such a phenomenon, we hypothesized that changes in PYY-(3–36) secretion should also be involved in the adverse effects of fasting on reproductive function. PYY-(3–36) release is regulated by food intake, increasing after meal intake and decreasing during fasting (3, 59). On the basis of this secretory profile, reduction of gonadotropin secretion during fasting would be due, at least in part, to the decrease in PYY-(3–36) release. To confirm this hypothesis, we have analyzed the effects in vivo and in vitro of PYY-(3–36) on gonadotropin secretion in controls fed ad libitum and in fasted rats. In adult male rats, deprivation of food for 4 days significantly decreased serum LH concentrations (Table 1). Intracerebroventricular administration of PYY-(3–36) stimulated more efficiently LH secretion in fasted than in control animals fed ad libitum, and serum LH concentrations reached levels higher than obtained in control males. The increased in vivo efficiency of PYY-(3–36) in fasted animals was confirmed in vitro. These results support our hypothesis that depression of gonadotropin secretion during fasting in adult animals may be due, at least partially, to the decrease in the stimulatory effect carried out by PYY-(3–36) and that the efficiency of this signal was increased during food deprivation.

To analyze the participation of GnRH on the stimulatory effect of icv administration of PYY-(3–36) on gonadotropin release in adult fasted rats, we analyzed the effects of PYY-(3–36) after pretreatment with a GnRH-ANT. Results obtained demonstrated that the blockade of GnRH action abolished the stimulatory effect of PYY-(3–36) on gonadotropin secretion. In addition, we analyzed in vitro the GnRH release in the presence of PYY-(3–36). Two important findings were observed: PYY-(3–36) inhibited GnRH release by hypothalamus obtained from males fed ad libitum, which agrees with data obtained in prepubertal males (17), whereas a clear stimulatory effect was observed after fasting. The reasons for the switch from an inhibitory action of PYY-(3–36) on GnRH release in control males to the stimulatory effect observed after fasting are unknown at the present. However, this finding is in strong agreement with the potentiation of PYY-(3–36) effectiveness on gonadotropin secretion after fasting. Overall, it is evident that the control of GnRH/gonadotropin release by PYY-(3–36) is critically dependent on nutritional status. Because the effects of PYY-(3–36) on GnRH are opposite in fasted and ad libitum-fed rats, the stimulatory effect on LH observed in both groups of animals suggests either that PYY-(3–36) modulated the hypothalamic release of different signals other than GnRH involved in the control of LH or that a possible direct pituitary effect (via hypothalamic-pituitary-portal system) of the peptide icv delivered.

The present data also indicate that PYY-(3–36) directly increases LH and FSH secretion in both sexes at the pituitary level, in accord with data obtained in prepubertal rats (17). The stimulatory effect is enhanced after fasting. The mechanisms of the stimulatory action of PYY-(3–36) at the pituitary level and the reasons for its increase effectiveness during fasting are unknown. It has been previously shown that the NPY Y2 and Y5 receptor mRNA expression patterns in hypothalamus do not change during fasting, in contrast with the increase observed for Y1 mRNA expression (11, 63), but the expression in pituitary has not been studied. To analyze whether in our experimental paradigm fasting increased the expression of genes encoding Y2 and Y5 receptors, we studied their expression levels in hypothalamus and pituitary. The fact that similar levels of mRNA were detected after fasting argues against the possibility that an upregulation of NPY Y2 and Y5 receptors in hypothalamus and/or pituitary might explain the increase in the effectiveness of PYY-(3–36) in fasted rats. Nonetheless, the possibility that fasting-induced changes in receptor number of signaling might take place at a posttrascriptional level cannot be ruled out on the basis of our present data.

Leptin stimulates GnRH and LH secretion (64), and serum leptin levels decreased during fasting (1). Different experimental approaches demonstrated the cross talk between leptin and NPY in the control of reproductive function. For example, the inhibition of gonadotropic axis in leptin-deficient mice is attenuated by removal of the NPY Y1 receptor, and acceleration of puberty by leptin is largely facilitated in mice deficient for NPY Y1 receptors (22). It is conceivable that suppression of leptin input to GnRH neurons and pituitary gonadotropes in fasted rats may enhance the responsiveness to other stimulating signals such as PYY-(3–36). If this hypothesis is correct, the increased hypothalamic/pituitary responsiveness to PYY-(3–36) after fasting could be secondary to the decrease in serum leptin levels. Because undernutrition induces, in addition to changes observed in serum leptin concentrations, a decrease in serum levels of insulin and an increase in those of corticosterone, and both hormones are involved in the control of LH secretion (10, 34, 37), the possibility that these changes could be involved in the potentiation of stimulatory effect of PYY-(3–36) after fasting merits further investigation.

In conclusion, the present experiments have demonstrated that the stimulatory effect of PYY-(3–36) on gonadotropin secretion is enhanced after fasting. This phenomenon included an increase in gonadotropin responsiveness to PYY-(3–36) in vivo and in vitro as well as a clear stimulatory effect on GnRH release. We propose that the inhibition of pituitary gonadotropin secretion that occurs in undernutrition can be mediated, at least in part, by the decrease in PYY-(3–36) secretion and is reversed by exogenous administration of the peptide.


   GRANTS
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REFERENCES
 
This work was supported by grants BFI 2000-0419-CO3 and BFI 2002-00176 from DGESIC (Ministerio de Ciencia y Tecnología, Spain).


   ACKNOWLEDGMENTS
 
The collaboration of A. Mayen is recognized.


   FOOTNOTES
 

Address for reprint requests and other correspondence: E. Aguilar, Physiology Section, Dept. of Cell Biology, Physiology and Immunology, Faculty of Medicine, Univ. of Córdoba, Avda. Menéndez Pidal s/n, 14004 Córdoba, Spain (e-mail: fi1agbee{at}uco.es)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

* These authors contributed equally to this work and should be considered as joint first authors. Back


   REFERENCES
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 ABSTRACT
 MATERIAL AND METHODS
 RESULTS
 DISCUSSION
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 REFERENCES
 

  1. Aubert ML, Pierroz DD, Gruaz NM, d’Alleves V, Vuagnat BA, Pralong FP, Blum WF, and Sizonenko PC. Metabolic control of sexual function and growth: role of neuropeptide Y and leptin. Mol Cell Endocrinol 140: 107–113, 1998.[CrossRef][ISI][Medline]
  2. Barreiro ML and Tena-Sempere M. Ghrelin and reproduction: a novel signal linking energy status and fertility? Mol Cell Endocrinol 226: 1–9, 2004.[CrossRef][ISI][Medline]
  3. Batterham RL, Cowley MA, Small CJ, Herzog H, Cohen MA, Dakin CL, Wren AM, Brynes AE, Low MJ, Ghatei MA, Cone RD, and Bloom SR. Gut hormone PYY-(3–36) physiologically inhibits food intake. Nature 418: 650–654, 2002.[CrossRef][Medline]
  4. Bauer-Dantoin AC, McDonald JK, and Levine JE. Neuropeptide Y potentiates luteinizing hormone (LH)-releasing hormone-induced LH secretion only under conditions leading to preovulatory LH surges. Endocrinology 131: 2946–2952, 1992.[Abstract]
  5. Bauer-Dantoin AC, Tabesh B, Norgle JR, and Levine JE. RU486 administration blocks neuropeptide Y potentiation of luteinizing-hormone (LH)-releasing hormone-induced LH surges in proestrous rats. Endocrinology 133: 2418–2423, 1993.[Abstract]
  6. Bergendahl M, Perheentupa A, and Huhtaniemi I. Effect of short-term starvation on reproductive hormone gene expression, secretion and receptor levels in male rats. J Endocrinol 121: 409–417, 1989.[Abstract]
  7. Bergendahl M, Perheentupa A, and Huhtaniemi I. Starvation-induced suppression of pituitary-testicluar function in rats is reversed by pulsatile gonadotropin-releasing hormone. Biol Reprod 44: 413–419, 1991.[Abstract]
  8. Cagampang FR, Ohjura S, Tsukamura H, Coen CW, Ota K, and Maeda K. Alpha 2-adrenegic receptors are involved in the suppression of luteinizing hormone release during acute fasting in the ovariectomized estradiol-primed rats. Neuroendocrinology 56: 724–728, 1992.[ISI][Medline]
  9. Catzeflis C, Pierroz DD, Rohner-Jeanrenaud F, Rivier JE, Sizonenko PC, and Aubert ML. Neuropeptide Y administered chronically into the lateral ventricle profoundly inhibits both the gonadotropic and the somatotropic axis in intact adult female rats. Endocrinology 132: 224–234, 1993.[Abstract]
  10. Chang LL, Kau MM, Wum WS, Ho LT, and Wang PS. Effects of fasting on corticosterone production by zona fasciculate-reticularis cells in ovariectomized rats. J Invest Med 50: 86–94, 2002.[ISI][Medline]
  11. Cheng X, Broberger C, Tong Y, Yongtao X, Yu G, Zhang X, and Hokfelt T. Regulation of expression of neuropeptide Y Y1 and Y2 receptors in the arcuate nucleus of fasted rats. Brain Res 792: 89–96, 1998.[CrossRef][ISI][Medline]
  12. Chomczynski P and Sacchi N. Single-step method of RNA isolation by acid guanidinium thiocianate-phenol-chloroform extraction. Anal Biochem 162: 156–159, 1987.[ISI][Medline]
  13. Coll AP, Challis BG, and O’Rahilly S. Peptide YY 3–36 and satiety: clarity or confusion? Endocrinology 145: 2582–2584, 2004.[Free Full Text]
  14. Crowley WR, Shah GV, Carroll BL, Kennedy D, Dockter ME, and Kalra SP. Neuropeptide-Y enhances luteinizing hormone (LH)-releasing hormone-induced LH release and elevations in cytosolic Ca2+ in rat anterior pituitary cells: evidence for involvement of extracellular Ca2+ influx through voltage-sensitive channels. Endocrinology 127: 1487–1494, 1990.[Abstract]
  15. Dryden S, Pickavana L, Frankish HM, and Williams G. Increased neuropeptide Y secretion in the hypothalamic paraventricular nucleus of obese (fa/fa) Zucker rats. Brain Res 690: 185–188, 1995.[CrossRef][ISI][Medline]
  16. Dumont Y, Jacques D, Bouchard P, and Quirion R. Species differences in the expression and distribution of the neuropeptide Y Y1, Y2, Y4 and Y5 receptors in rodents, guinea pig, and primate brains. J Comp Neurol 402: 372–384, 1998.[CrossRef][ISI][Medline]
  17. Fernández-Fernández R, Aguilar E, Tena-Sempere M, and Pinilla L. Effects of polypeptide YY3–36 upon luteinizing hormone-releasing hormone and gonadotropin secretion in prepubertal rats: in vivo and in vitro studies. Endocrinology 146: 1403–1410, 2005.[Abstract/Free Full Text]
  18. Fraley GS and Kuenzel WJ. Precocious puberty in chicks (Gallus domesticus) induced by central injections of neuropeptide Y. Life Sci 52: 1649–1656, 1993.[CrossRef][ISI][Medline]
  19. Freeman ME. Editorial. Neuropeptide Y: a unique member of the constellations of gonadotropin-releasing hormones. Endocrinology 133: 2411–2412, 1993.[CrossRef][ISI][Medline]
  20. Frisch R and McArthur J. Menstrual cycles: fatness as a determinant of minimum weight for height necessary for their maintenance or onset. Science 169: 397–399, 1974.
  21. Frisch R and Revelle R. Height and weight at menarche: a hypothesis of critical body weights and adolescent events. Science 169: 397–399, 1970.[Abstract/Free Full Text]
  22. Gonzales C, Voirol MJ, Giacomini M, Gaillard RC, Pedrazzini T, and Pralong FP. The neuropeptide Y Y1 receptor mediates NPY-induced inhibition of the gonadotrope axis under poor metabolic conditions. FASEB J 18: 137–139, 2004.[Abstract/Free Full Text]
  23. Gore AC, Mitsushima D, and Teresawa E. A possible role of neuropeptide Y in the control of the onset puberty in female rhesus monkey. Neuroendocrinology 58: 23–34, 1993.[ISI][Medline]
  24. Halatchev IG, Ellacott KLJ, Fan W, and Cone RD. Peptide YY 3–36 inhibits food intake in mice through a melanocortin-4-receptor-independent mechanism. Endocrinology 145: 2585–2590, 2004.[Abstract/Free Full Text]
  25. Jain MR, Pu S, Kalra PS, and Kalra SP. Evidence that stimulation of two modalities of pituitary luteinizing hormone release in ovarian steroid-primed ovariectomized rats may involve neuropeptide Y Y1 and Y4 receptors. Endocrinology 140: 5171–5177, 1999.[Abstract/Free Full Text]
  26. Kalra SP and Crowley WR. Neuropeptide Y: a novel neuroendocrine peptide in the control of pituitary hormone secretion and its relation to luteinizing hormone. Front Neuroendocrinol 13: 1–46, 1992.[ISI][Medline]
  27. Kalra SP, Dube MG, Pu S, Xu B, Horvath TL, and Kalra PS. Interacting appetite-regulating pathways in the hypothalamic regulation of body weight. Endocr Rev 20: 68–100, 1999.[Abstract/Free Full Text]
  28. Kalra SP and Kalra PS. Do testosterone and estradiol-17 beta enforce inhibition or stimulation of luteinizing hormone-releasing hormone secretion? Biol Reprod 41: 559–570, 1989.[Abstract]
  29. Kalra SP and Kalra PS. Neural regulation of luteinizing hormone secretion in the rat. Endocr Rev 4: 311–351, 1983.[ISI][Medline]
  30. Kalra SP and Kalra PS. NPY an endearting journey in search of a neurochemical on/off switch for appetite, sex and reproduction. Peptides 25: 465–471, 2004.[CrossRef][ISI][Medline]
  31. Kalra SP and Kalra PS. Nutritional infertility in the role of the interconnected hypothalamic neuropeptide Y-galanin-opioid network. Front Neuroendocrinol 17: 371–401, 1996..[CrossRef][ISI][Medline]
  32. Kalra SP, Xu B, Dube MG, Moldawer LL, Martin D, and Kalra PS. Leptin and ciliary neurotropic factor (CNTF) inhibit fasting-induced suppression of luteinizing hormone release in rats: role of neuropeptide Y. Neurosci Lett 240: 45–49, 1998.[CrossRef][ISI][Medline]
  33. Kalra SP. Appetite and body weight regulation: is it all in the brain? Neuron 19: 227–230, 1997.[CrossRef][ISI][Medline]
  34. Kamel F and Kubajak CL. Modulation of gonadotropin secretion by corticosterone: interaction with gonadal steroids and mechanism of action. Endocrinology 121: 561–568, 1987.[Abstract]
  35. Keene AC, Jones JE, Wade GN, and Corp ES. Forebrain sites of NPY action on estrous behavior in Syrian hamsters. Physiol Behav 78: 711–716, 2003.[CrossRef][Medline]
  36. Keire DA, Mannon P, Kobayashi M, Walsh JH, Solomon TE, and Reeve JR Jr. Primary structures of PYY, [Pro(34)] PYY, and PYY-(3–36) confer different conformations and receptor selectivity. Am J Physiol Gastrointest Liver Physiol 279: G126–G131, 2000.[Abstract/Free Full Text]
  37. Kovacs P, Parlow AF, and Karkanias GB. Effect of centrally administered insulin on gonadotropin-releasing hormone neuron activity and luteinizing hormone surge in the diabetic female rat. Neuroendocrinology 76: 357–365, 2002.[CrossRef][ISI][Medline]
  38. Leonhardt S, Shahab M, Luft H, Wuttke W, and Jarry H. Reduction of luteinizing hormone secretion induced by long-term feed restriction in male rats is associated with increased expression of GABA-synthesizing enzymes without alterations of GnRH expression. J Neuroendocrinol 11: 613–619, 1999.[CrossRef][ISI][Medline]
  39. Maeda K, Cagampang FR, Coen CW, and Tsukamura H. Involvement of the catecholaminergic input to the paraventricular nucleus and corticotrophin-releasing hormone in the fasting-induced suppression of luteinizing hormone release in female rats. Endocrinology 134: 1718–1722, 1994.[Abstract]
  40. Maeda K and Tsukamura H. Neuroendocrine mechanism mediated fasting-induced suppression of luteinizing hormone secretion in female rats. Acta Neurobiol Exp (Wars) 56: 787–796, 1996.
  41. McCann SM, Krulich L, Cooper KJ, Kalra PS, Kalra SP, Libertun C, Negro-Vilar A, Orias R, Ronnekleiv O, and Fawcett CP. Hypothalamic control of gonadotrophin and prolactin secretion, implications for fertility control. J Reprod Fertil Suppl 20: 43–59, 1973.[Medline]
  42. Minami S, Frautschy SA, Plotsky PM, Sutton SW, and Sarkar DK. Facilitatory role of neuropeptide Y on the onset of puberty: effect of immunoneutralization of neuropeptide Y on the release of luteinizing hormone and luteinizing-hormone releasing hormone. Neuroendocrinology 52: 112–115, 1990.[ISI][Medline]
  43. Minami S and Sarkar DK. Central administration of neuropeptide Y induces precocious puberty in female rats. Neuroendocrinology 56: 930–934, 1992.[ISI][Medline]
  44. Nagatani S, Guthikonda P, Thompson RC, Tsukamura H, Maeda KI, and Foster DL. Evidence for GnRH by leptin: leptin administration prevents reduced pulsatile LH secretion during fasting. Neuroendocrinology 67: 370–376, 1998.[CrossRef][ISI][Medline]
  45. Navarro VM, Fernández-Fernández R, Castellano JM, Roa J, Mayén A, Barreiro ML, Gaytán F, Aguilar E, Pinilla L, Diéguez C, and Tena-Sempere M. Advanced vaginal opening and precocious activation of the reproductive axis by kiss-1 peptide, the endogenous ligand of GPR54. J Physiol 561: 379–386, 2004.[Abstract/Free Full Text]
  46. Pelleymounter MA, Cullen MJ, Baker MB, Hecht R, Winters D, Boone T, and Collins F. Effects of the obese gene product on the body weight regulation in ob/ob mice. Science 269: 540–543, 1995.[Abstract/Free Full Text]
  47. Pierroz DD, Catzeflis C, Aebi AC, Rivier JE, and Aubert ML. Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insuline-like growth factor I secretion in intact adult male rats. Endocrinology 137: 3–12, 1996.[Abstract]
  48. Pinilla L, González L, Tena Sempere M, and Aguilar E. Activation of AMPA receptors inhibits prolactin and estradiol secretion and delays the onset of puberty in female rats. J Steroid Biochem Mol Biol 75: 277–281, 2000.
  49. Pralong FP, Voirol MJ, Giacomini M, Gaillard RC, and Grouzmann E. Acceleration of pubertal development following central blockade of the Y1 subtype of neuropeptide Y receptors. Regul Pept 95: 47–52, 2000.[CrossRef][ISI][Medline]
  50. Prasanth KC, Haver AC, and Reidelberger RD. Intravenous infusion of peptide YY (3–36) potently inhibits food intake in rats. Endocrinology 146: 1879–1888, 2005.
  51. Raposinho PD, Broqua P, Pierroz DD, Hayward A, Dumont Y, Quirion R, Junien JL, and Aubert ML. Evidence that the inhibition of luteinizing hormone secretion exerted by central administration of neuropeptide Y (NPY) in the rat is predominantly mediated by the NPY Y5 receptor subtype. Endocrinology 140: 4046–4055, 1999.[Abstract/Free Full Text]
  52. Russell SH, Small CJ, Kennedy AR, Stanley SA, Seth A, Murphy KG, Taheri S, Ghatei MA, and Bloom SR. Orexin A interactions in the hypothalamo-pituitary gonadal axis. Endocrinology 142: 5294–5302, 2001.[Abstract/Free Full Text]
  53. Sutton SW, Toyama TT, Otto S, and Plotsky PM. Evidence that neuropeptide Y (NPY) released into the hypophysial portal circulation participates in priming gonadotropes to the effects of gonadotropin releasing hormone (GnRH). Endocrinology 123: 1208–1210, 1988.[Abstract]
  54. Tatemoto K. Neuropeptide Y: complete amino acid sequence of the brain peptide. Proc Natl Acad Sci USA 79: 5485–5489, 1982.[Abstract/Free Full Text]
  55. Tena-Sempere M, Barreiro ML, González LC, Gaytán F, Zhang FP, Caminos JE, Pinilla L, Casanueva FF, Diéguez C, and Aguilar E. Novel expression and functional role of ghrelin in rat testis. Endocrinology 143: 717–725, 2002.[Abstract/Free Full Text]
  56. Tena-Sempere M and Barreiro ML. Leptin in male reproduction: the testis paradigm. Mol & Cell Endocrinol 188: 9–13, 2002.[CrossRef][ISI][Medline]
  57. Tena-Sempere M, Pinilla L, and Aguilar E. Orchidectomy selectively increases follicle-stimulating hormone secretion in gonadotropin-releasing hormone antagonist-treated rats. Eur J Endocrinol 132: 357–362, 1995.[Abstract]
  58. Tena-Sempere M, Pinilla L, Zhang FP, González LC, Huhtaniemi I, Casanueva FF, Diéguez C, and Aguilar E. Developmental and hormonal regulation of leptin receptor (Ob-R) messenger ribonucleic acid expression in the rat testis. Biol Reprod 64: 634–643, 2001.[Abstract/Free Full Text]
  59. Tovar S, Seoane LM, Caminos JE, Nogueiras R, Casanueva FF, and Dieguez C. Regulation of peptide YY levels by age, hormonal and nutritional status. Obes Res 12: 1944–1952, 2004.[ISI][Medline]
  60. Tschop M, Castaneda TR, Joost HG, Thone-Reineke C, Ortmann S, Klaus S, Hagan MM, Chandler PC, Oswald KD, Benoit SC, Seeley RJ, Kinzig KP, Moran TH, Beck-sickinger AG, Koglin N, Rodgers RJ, Blundell JE, Ishii Y, Beattie AH, Holch P, Allison DB, Raun K, Madsen K, Wulff BS, Stidsen CE, Birringer M, Kreuzer OJ, Schindler M, Arndt K, Rudolf K, Mark M, Deng XY, Withcomb DC, Halem H, Taylor J, Dong J, Datta R, Culler M, Craney S, Flora D, Smiley D, and Heiman ML. Physiology: does gut hormone PYY-3–36 decrease food intake in rodents? Nature 431: 430–431, 2004.[CrossRef][Medline]
  61. Wade GN and Schneider JE. Metabolic levels and reproduction in female mammals. Neurosci Biobehav Rev 16: 235–272, 1992.[CrossRef][ISI][Medline]
  62. Xiao Q, Han X, Arany E, Hill D, Challis JR, and McDonald TJ. Human placenta and fetal membranes contain peptide YY1–36 and peptide YY3–36. J Endocrinol 156: 485–492, 1998.[Abstract]
  63. Xu B, Kalra PS, Moldawer LL, and Kalra SP. Increased appetite augments hypothalamic NPY Y1 receptor gene expression: effects of anorexigenic ciliary neurotropic factor. Regul Pept 75–76: 391–395, 1998.
  64. Yu WH, Kimura M, Walczewska A, Karanth S, and McCann SM. Role of leptin in hypothalamic-pituitary function. Proc Natl Acad Sci USA 94: 1023–1028, 1997.[Abstract/Free Full Text]



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L. Pinilla, R. Fernandez-Fernandez, J. Roa, J. M. Castellano, M. Tena-Sempere, and E. Aguilar
Selective role of neuropeptide Y receptor subtype Y2 in the control of gonadotropin secretion in the rat
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