Submitted on April 8, 2005
Accepted on September 3, 2005
INCREASED CIRCADIAN PROLACTIN RELEASE IS BLUNTED AFTER BODY WEIGHT LOSS IN OBESE PREMENOPAUSAL WOMEN
Petra Kok1*, Ferdinand Roelfsema2, Janneke G Langendonk1, Caroline C de Wit1, Marijke Frolich3, Jacobus Burggraaf4, Edo A Meinders1, and Hanno Pijl2
1 Department of General Internal Medicine, Leiden University Medical Center, Leiden, The Netherlands
2 Department of Endocrinology and Metabolic diseases, Leiden University Medical Center, Leiden, The Netherlands
3 Department of Clinical Chemistry, Leiden University Medical Center, Leiden, The Netherlands
4 Center for Human Drug Research, Leiden University Medical Center, Leiden, The Netherlands
* To whom correspondence should be addressed. E-mail: p.kok{at}lumc.nl.
We recently showed that PRL release is considerably enhanced in obese women in proportion to the size of their visceral fat mass. PRL release is inhibited by dopamine 2 receptor (D2R) activation and dietary restriction/weight loss are associated with increased dopaminergic signalling in animals. Therefore, we hypothesized that enhanced PRL release in obese humans would be reversed by weight loss. To evaluate this postulate, we measured 24 h plasma PRL concentrations at 10 min intervals in eleven obese premenopausal women (BMI 33.3 ± 0.7 kg/m2) before and after weight loss (50% reduction of overweight/ 15% absolute weight loss, using a very low calorie diet) in the follicular phase of their menstrual cycle. The 24 h PRL concentration profiles were analyzed by a peak detection program (Cluster) and a waveform-independent deconvolution technique (Pulse). Spontaneous 24 h PRL secretion was significantly reduced in obese women (mean daily release before 128 ± 24 vs. after weight loss 110 ± 17 µg/Vdlx24h, P = 0.05). Body weight loss particularly blunted PRL secretory burst mass (Pulse area before 230 ± 28 vs. after weight loss 221 ± 31 µg /Vdlxmin, P = 0.03), whereas burst frequency was unaffected (Number of pulses before 11 ± 1 vs. after weight loss 12 ± 1 n/24h, P = 0.69). Thus, elevated PRL secretion rate in obese women is significantly reduced after loss of 50% of overweight. We speculate that amelioration of deficit dopamine D2 receptor mediated neurotransmission and/or diminutions of circulating leptin/estrogen levels might be involved in the physiology of this phenomenon.
