Melatonin inhibits GnRH-induced Ca2+ mobilization and influx through voltage-regulated channels.
In neonatal rat gonadotrophs, melatonin acts through the high-affinity membrane-bound receptors to inhibit GnRH-induced [Ca2+]i increase. GnRH increases [Ca2+]i primarily by mobilization from the inositol trisphosphate-sensitive pool followed by Ca2+ influx through the voltage-sensitive channels. Melatonin inhibits the GnRH-induced [Ca2+]i increase. When added after the GnRH-induced spike, melatonin decreases [Ca2+]i in 52% of the gonadotrophs. The effect of melatonin is dependent on extracellular Ca2+ and may be mimicked by Ca2+-free medium or verapamil. When added before GnRH, melatonin inhibits the [Ca2+]i spike. This effect of melatonin is independent of extracellular Ca2+ as it persists in Ca2+-free medium. These findings indicate that melatonin blocks Ca2+ mobilization as well as Ca2+ influx in the gonadotrophs.
Slanar
O
O
Institute of Physiology, Academy of Sciences of the Czech Republic, Videnska, Prague.
Zemkova
H
H
Vanecek
J
J
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015640:Ion Channel Gating; D008550:Melatonin / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology; D051381:Rats; D017208:Rats, Wistar
D015220:Calcium Channels; D007987:Gonadotropin-Releasing Hormone; D008550:Melatonin; D002118:Calcium