AJP - Endocrinology and Metabolism, Vol 268, Issue 4 E758-E765, Copyright © 1995 by American Physiological Society
Cold exposure attenuates effects of secretagogues on serum prolactin and growth hormone levels in male rats
P. Rauhala, J. J. Idanpaan-Heikkila, A. Lang, R. K. Tuominen and P. T. Mannisto
Department of Pharmacology and Toxicology, University of Helsinki, Finland.
The stimulatory effect of morphine, dexmedetomidine (an alpha
2-adrenoceptor agonist), 1-(3-chlorophenyl)-piperazine (m-CPP, a 5-HT1B
agonist), U-50488H (a kappa-opioid receptor agonist), pimozide (a dopamine
antagonist), and restraint stress on prolactin and growth hormone (GH)
secretion was compared during cold exposure (4 degrees C) and under basal
conditions (30 degrees C) in male rats. Rectal temperature was also
measured. The stimulatory effect of morphine, dexmedetomidine, m-CPP, and
partially U-50488H on prolactin secretion was attenuated in rats kept at 4
degrees C. Cold exposure did not abolish prolactin release induced by
pimozide and restraint stress. Cold exposure also antagonized the effect of
morphine and dexmedetomidine on GH secretion. The stimulatory effect of
morphine on prolactin and GH secretion was restored in the warm environment
despite the sustained hypothermia. Cold exposure blocked the stimulatory
effect of morphine on prolactin secretion in rats that were tolerant to the
hypothermic effect of morphine. Thus hypothermia caused by morphine,
dexmedetomidine, and m-CPP during cold exposure is not the sole factor in
the antagonistic effect of cold. We suggest that cold exposure releases
some compound(s) modulating hypothalamic neural pathways.
