Muscarinic stimulation of prostacyclin synthesis by the rat penis

An in vitro model for the investigation of PGI2 synthesis by the rat penis is described. Acetyl-beta-methylcholine (methacholine; MeCh) and carbamyl choline (carbachol) stimulated PGI2 synthesis in a dose-dependent manner (ED50 = 1.5 X 10(-6); 2.5 X 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/l)- and carbachol (10(-6) mol/l)-stimulated PGI2 synthesis was inhibited by atropine in a dose-dependent manner (ID50 = 2.5 X 10(-7) mol/l; 7 X 10(-6) mol/l, respectively). The inhibition by atropine of MeCh-stimulated PGI2 synthesis was competitive. MeCh (10(-6) mol/l)-stimulated PGI2 synthesis was inhibited by verapamil (ID50 = 6 X 10(-5)) and calcium-free incubation media. It is concluded that in the rat penis PGI2 synthesis is principally under muscarinic control and is calcium transport-dependent. Since PGI2 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 PGI2 is also a potent inhibitor of platelet aggregation.