In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. III. Effect of neuropeptides on alpha-MSH secretion.
It has been previously demonstrated that thyrotropin-releasing hormone (TRH) stimulates in vitro the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in frog. In the present study, the effects of various neuropeptides on spontaneous and/or TRH-induced alpha-MSH secretion were investigated, using a well-defined perifusion system technique. Vasoactive intestinal peptide, (VIP) a neurohormone which stimulates TRH target cells in mammals, was totally devoid of effect on frog melanotrophs although VIP-like material could be detected in neurointermediate lobe extracts. Somatostatin-like immunoreactive material was found in high concentrations in the frog neurointermediate lobe complex, but synthetic somatostatin (from 10(-10) to 10(-6) M) did not modify the spontaneous release of alpha-MSH. At doses of 10(-8) and 10(-6) M, synthetic somatostatin did not modify TRH-induced alpha-MSH secretion. Morphine (10(-5) M) and opioid peptides (10(-10) to 10(-6) M) had no effect on spontaneous alpha-MSH secretion. In addition, methionine enkephalin (10(-5) M) did not modify the stimulatory effect of TRH on alpha-MSH secretion. From these results we conclude that, among the neuropeptides which modulate prolactin secretion in mammals, only TRH is involved in alpha-MSH secretion in the frog.
D000818:Animals; D004723:Endorphins / Q000494:pharmacology; D004743:Enkephalin, Leucine / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology; D010477:Perfusion / Q000379:methods; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011895:Rana ridibunda; D013004:Somatostatin / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D001615:beta-Endorphin
D004723:Endorphins; D014660:Vasoactive Intestinal Peptide; D013004:Somatostatin; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D013973:Thyrotropin-Releasing Hormone; D001615:beta-Endorphin; D009020:Morphine; D009074:Melanocyte-Stimulating Hormones