Effects of Adenosine Triphosphate on Relaxation of Rabbit Cavernosal Smooth Muscle

Park, Hong Seok; Kim, Je Jong

Abstract

Externally applied acetylcholine(Ach) in corpus cavernosum has been shown to cause endothelium dependent smooth muscle relaxation. ATP is accepted as a relaxant of smooth muscle by both a direct action and more powerful indirect action via the endothelial cells. Endothelium-derived relaxing factor(EDRF) is released with stimulation of acetylcholine or other endothelium dependent substances raise cGMP level within the smooth muscle cell and cause relaxation of smooth muscle. EDRF is known as nitric oxide(NO) and its actions are abolished by specific inhibitor of nitric oxide synthesis, such as L-n-monomethyl arginine(L-NMMA) or inhibitors of cyclic GMP synthesis, such as methylene blue(MB). In this study, we evaluated the action of ATP related with NO and compared effect of ATP with acetylcholine and bethanechol chloride in rabbit corpus cavernosal smooth muscle under organ bath. Changes in isometric tension of corporal strips were monitored. With pretreatment L-NMMA or MB, relaxing effects of acetylcholine or bethanechol chloride in corporal strips were completely inhibited, but relaxing effects of ATP were not altered. These data suggested that nitric oxide plays a crucial role in cholinergically induced cavernosal smooth muscle relaxation. ATP mediated rabbit corporal smooth muscle relaxation was not affected by inhibitors of nitric oxide synthesis and independent of cyclic GMP accumulation.