Role of the L‐arginine/nitric oxide pathway in relaxation of isolated human penile cavernous tissue and circumflex veins

Publisher Website
Google Scholar
Abstract
In human penile corpus cavernosum strips, pre‐contracted by noradrenaline, electrical stimulation of nerves evoked non‐adrenergic, non‐cholinergic (NANC) relaxant responses which could be inhibited by tetrodotoxin 10‐6M, NG‐nitro‐L‐arginine (L‐NNA) 10‐7‐10‐4M, and oxyhaemoglobin 10‐5M, but not by methylene blue (MB) 10‐5M. Acetylcholine‐induced relaxations were also inhibited by L‐NNA 10‐4M and oxyhaemoglobin 10‐5M, but were unaffected by pyrogallol 10‐4M, MB 10‐6M, and tetrodotoxin 10‐6M. MB 5 × 10‐4‐10‐4M significantly reduced the responses to both electrical stimulation and to acetylcholine. Nitric oxide (NO) 10‐7‐10‐4M and sodium nitroprusside 10‐9‐10‐4M caused concentration‐dependent relaxations. The NO‐induced relaxations were inhibited by oxyhaemoglobin 10‐5M, and the concentration‐response curve for sodium nitroprusside was shifted to the right by MB 10‐5M. The response to sodium nitroprusside was unaffected by L‐NNA 10‐4M, oxyhaemoglobin 10‐5M, and pyrogallol 10‐4M. In circumflex veins, pre‐contracted by noradrenaline, no NANC‐mediated relaxation was found in response to electrical stimulation; acetylcholine caused endothelium‐dependent relaxations, which were insensitive to L‐NNA 10‐4M and oxyhaemoglobin 10‐5M. NO and sodium nitroprusside caused concentration‐dependent relaxations; the concentration‐response curves for NO and sodium nitroprusside were shifted to the right by oxyhaemoglobin 10‐5M. Removal of the endothelium left the NO‐ and sodium nitroprusside‐induced relaxations unchanged.The results confirm previous observations that relaxations of human corpus cavernosum induced by both NANC nerve stimulation and exogenous acetylcholine involve an agent derived from L‐arginine. No NANC response to electrical stimulation was found in circumflex veins, where acetylcholine induced an endothelium‐dependent relaxation, apparently independent of the L‐arginine/nitric oxide pathway.

This publication has 24 references indexed in Scilit: