Prostanoid synthesis by the rat urinary bladder: evidence for stimulation through muscarine receptor-linked calcium channels

Abstract

An in vitro model for the study of muscarine receptor-mediated synthesis of prostacyclin (PGI2) and other prostanoids (PGE2 and PGF2 alpha) by the rat urinary bladder is described. PGI2 synthesis was stimulated by parasympathomimetic agents (carbachol greater than methacholine greater than arecoline; McNA 343, nicotine and dimethyl phenyl piperazinium were without effect). Methacholine (3 X 10(-6) mol X l-1)-stimulated PGI2 synthesis was inhibited by muscarinic antagonists (atropine greater than ipratroprium bromide greater than gallamine greater than pirenzepine) and was completely abolished by the presence of ethylene diamine tetraacetic acid (EDTA: 10 mmol X l-1). Verapamil also inhibited methacholine-stimulated PGI2 synthesis in a dose-dependent manner. The antagonistic action of atropine was shown to be competitive, but had no effect on calcium ionophore A23187-stimulated PGI2 synthesis. High concentrations of [K+] (up to 0.11 mol X l-1) were without effect on PGI2 synthesis. PGE2, PGF2 alpha and PGI2 synthesis were all equally stimulated with methacholine, carbachol, arecoline and A23187, and methacholine-stimulated synthesis of these prostanoids was equally inhibited by atropine, ipratroprium bromide, gallamine, verapamil and EDTA. It is concluded that in vitro prostanoid synthesis by the rat urinary bladder: is stimulated by post ganglionic muscarine receptors; involves a muscarine receptor-linked calcium influx system; and is mediated by a predominance of M2 subtype receptors.