Effects ofmuscarinic receptor stimulation on the thyrotropin-induced thyroxine release inthe guinea pig thyroid
1999
Kim, H.H. | Kim, J.S. (Chonbuk National University, Chonju (Korea Republic). College of Vetrinary Medicine)
The present experiments were performed to examine the effects of acetylcholine (ACh) and carbachol (CC) on thyroxine (T4) release and any possible relation between inhibition of T4 relese and sighaling pathway in guinea pig thyroids. The thyroids were incubated in the medium containing the test agents, samples of the medium wer assayed for T4 by EIA kits. ACh and CC inhibited the TSH-stimulated T4 release. These inhibition were reversed by atropine, but not by d-tubocurarine. The ingibitory effects of ACh on T4 release were prevented by M1- and M3-muscarinic antagonists and its inhibition was also slightly reversed by M2- and M4- muscarinic antagonists. R59022, like ACh and CC, also inhibited the TSH-stimulated T4 release. This inhibition was reversed by protein kinase C inhibitor and Ca2+ channel blocker. The present study suggests that cholinergic inhibition of T4 release from thyroids can be induced mainly by ctivation of the M1- or M3-receptors and that it is mediated throught the muscarinic receptor-stimulated protein kinase C activation
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