Effects of castration on nitric oxide-mediated relaxations in male rat corpus cavernosum smooth muscle

BACKGROUND: The effects of castration on nitric oxide- mediated relaxations and nitric oxide synthase activity in male rat corpus cavernosum smooth muscles. METHODS: Eight-week-old male rats were assigned to two groups: control (sham operated) and castrated animals. After 8 weeks, corpus cavernosum smooth muscle strips were mounted in an organ bath for isometric tension recordings. Electrical field stimulation (EFS) was applied to the strips precontracted with 30 microM phenylephrine. The microdialysis probe was inserted into the strip, and Krebs-Henseleit solution was perfused into the probe. The dialysate during EFS and cholinergic stimulation was collected, and the amount of NO(-)(2)/NO(-)(3) (NOx) released in the dialysate was measured by the Greiss method. Sodium nitroprusside and carbachol were cumulatively added to the strips precontracted with 30 microM phenylephrine. RESULTS: EFS caused frequency-dependent relaxations and NOx releases in the strips. Pretreatment with N(omega)-nitro-L-arginine (100 microM) and tetrodotoxin (1 microM) completely inhibited relaxations and NOx releases. The maximum relaxation in the castration group was significantly greater than that in the control group. The release of NOx was significantly greater in the castration group than in the control group. Sodium nitroprusside relaxed the tissues in both groups similarly. Carbachol failed either to relax the tissue or to increase the amount of NOx production in the tissue. CONCLUSION: The present data suggest that castration enhances nitric oxide synthase activity and nitric oxide-mediated relaxations in the male rat corpus cavernosum.