Melatonin inhibits increase of intracellular calcium and cyclic AMP in neonatal rat pituitary via independent pathways.
In neonatal rat pituitary, melatonin inhibits GnRH-induced increase of cAMP and [Ca2+]i. Both effects are transduced by specific high-affinity melatonin receptors coupled with pertussis toxin-sensitive G-protein. We have attempted to determine whether melatonin acts via independent pathways on both messengers or whether the indole directly inhibits only one of the messengers and the second is decreased as a secondary consequence. Melatonin inhibition of cAMP accumulation was not prevented by agents known to block melatonin effect on [Ca2+]i such as Na(+)- or Ca2(+)-free medium, Bay K, nifedipine, KCl or gramicidin. Melatonin effect on [Ca2+]i was not prevented by forskolin or 8-bromo-cAMP. We therefore conclude that melatonin inhibits cAMP accumulation and [Ca2+]i increase independently by separate pathways.
Vanecek
J
J
Institute of Physiology, Academy of Sciences of Czech Republic, Prague.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism; D044094:Receptors, Melatonin; D015290:Second Messenger Systems
D011956:Receptors, Cell Surface; D044094:Receptors, Melatonin; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D008550:Melatonin; D002118:Calcium