IN GH3 PITUITARY-CELLS, ACETYLCHOLINE AND VASOACTIVE INTESTINAL PEPTIDE ANTAGONISTICALLY MODULATE ADENYLATE-CYCLASE, CYCLIC-AMP CONTENT, AND PROLACTIN SECRETION

  • 1 January 1983
    • journal article
    • research article
    • Vol. 24  (2) , 189-194
Abstract
In rat GH3 pituitary cell homogenates, acetylcholine (ACh) (IC50 [median inhibitory concentration] 200 nM) inhibits adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in a concentration- and GTP-dependent manner. Maximal inhibition was obtained with 10 .mu.M ACh and corresponded to approximately a 50% decrease in basal enzyme activity. ACh inhibition is antagonized by atropine and is mimicked by muscarinic receptor agonists [oxotremorine, carbachol and methacholine], but not by nicotine. ACh reduces the adenylate cyclase stimulation by vasoactive intestinal peptide (VIP), without changing its EC50 [median effective concentration]. In intact GH3 cells, ACh decreases the cAMP content and the rate of prolactin release in a concentration-dependent manner. When the cells are simultaneously exposed to VIP and ACh, the VIP-induced increases in cAMP accumulation and prolactin release are reduced by 80% and 40%, respectively. The potency of VIP is not significantly changed by the presence of ACh, and vice versa.