The effects of castration on relaxation of rat corpus cavernosum smooth muscle in vitro

Purpose: This study was conducted to investigate the role of testosterone (T) in regulating the relaxation of isolated rat corpus cavernosum strips in vitro. Materials and Methods: Male rats were divided into treatment groups of intact, castrate, and castrate with T replacement. Norepinephrine (NE) was added to contract each of the tissue strips. Next, sodium nitroprusside (SNP), experiment I, or 8-Br-cGMP, experiment II, was added to relax the cavernosum tissue. Percent relaxations were recorded for each treatment group at each dose level. Results: SNP was added to the NE-contracted tissues in doses of 10(-4) and 10(-3) M. In this experiment, castration significantly reduced tissue responsiveness to SNP and T replacement restored the response to intact levels. In the second experiment 8-Br-cGMP was added to the NE-contracted tissues in doses of 10(-5) and 10(-4) M. 8-Br-cGMP 10(-4) M was significantly less effective in relaxing tissue from castrate animals as compared with intact controls. Again, T treatment restored the response to intact levels. Conclusions: Our results show a clear role of T in regulating the ability of corpus cavernosum tissue to relax when treated with SNP or 8-Br-cGMP in vitro. In addition, the data suggests that T regulates sites distal to the formation of cGMP in the relaxation pathway.