Muscarinic stimulation of prostacyclin synthesis by the rat penis

Abstract

An in vitro model for the investigation of PGI 2 synthesis by the rat penis is described. Acetyl-β-methylcholine (methacholine; MeCh) and carbamyl choline (carbachol) stimulated PGI 2 synthesis in a dose-dependent manner (ED 50 = 1.5 × 10 −6; 2.5 × 10 −6, respectively), whereas adrenaline, noradrenaline, histamine, serotonin, vasoactive intestinal polypeptide (VIP), nicotine, dimethyl phenylpiperazinium (DMPP) and adenosine triphosphate (ATP) were without effect. MeCh (10 −6 mol/1)- and carbachol (10 −6 mol/1)-stimulated PGI 2 synthesis was inhibited by atropine in a dose-dependent manner (ID 50 = 2.5 × 10 −7mol/1; 7 × 10 −6mol/1, respectively). The inhibition by atropine of MeCh-stimulated PGI 2 synthesis was competitive. MeCh (10 −6 mol/1)-stimulated PGI 2 synthesis was inhibited by verapamil (ID 50 = 6 × 10 −5) and calcium-free incubation media. It is concluded that in the rat penis PGI 2 synthesis is principally under muscarinic control and is calcium transport-dependent. Since PGI 2 is a vasodilator, these findings may be relevant to the increased blood flow into the penis associated with penile erection. They may also be relevant to the protection of the penile vasculature from thrombosis, since PGI 2 is also a potent inhibitor of platelet aggregation.