Morning administration of melatonin antagonizes the antigonadotrophic effect of afternoon injections of melatonin, 5-methoxytryptophol and arginine vasotocin in intact mice.
In intact prepubertal mice kept under a long photoperiod subcutaneous afternoon (4:30 p.m.) injections (20 micrograms) but not morning (9:30 a.m.) injections (100 micrograms) of melatonin and 5-methoxytryptophol elicited antigonadotrophic effects. A morning dose (100 micrograms) of methoxytryptophol abolished the antigonadotrophic effects of afternoon injections of methoxytryptophol. Similarly the antigonadotrophic effects of afternoon injections of melatonin, 5-methoxytryptophol and arginine vasotocin could be partially destroyed by 100 micrograms and completely abolished by 1 mg melatonin administered in the morning.
D000818:Animals; D004334:Drug Administration Schedule; D005260:Female; D006062:Gonadotropins / Q000037:antagonists & inhibitors*; D007211:Indoles / Q000037:antagonists & inhibitors*; D008297:Male; D008550:Melatonin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051379:Mice; D008813:Mice, Inbred ICR; D009929:Organ Size / Q000187:drug effects; D010053:Ovary / Q000187:drug effects; D011467:Prostate / Q000187:drug effects; D012669:Seminal Vesicles / Q000187:drug effects; D013737:Testis / Q000187:drug effects; D014599:Uterus / Q000187:drug effects; D014668:Vasotocin / Q000037:antagonists & inhibitors*
D006062:Gonadotropins; D007211:Indoles; C002465:methoxytryptophol; D008550:Melatonin; D014668:Vasotocin