EFFECTS OF CASTRATION ON ADRENERGIC, CHOLINERGIC AND NONADRENERGIC, NONCHOLINERGIC RESPONSES OF ISOLATED CORPUS CAVERNOSUM FROM RABBIT

Objective To investigate the effects of castration and testosterone on the constricting effect of phenylephrine and endothelium-dependent an d -independent relaxing effects of different agonists in the corpus ca vernosum of male rabbits. Materials and methods Twenty rabbits were ca strated and 10 received testosterone replacement for I month after cas tration: 10 further rabbits underwent a sham operation and acted as co ntrols. One month after operation the rabbits were killed and their pe nises excised. Strips of corpus cavernosum were used for isometric ten sion measurements in organ chambers; concentration-response relationsh ips for phenylephrine, carbachol, adenosine and sodium nitroprusside w ere obtained by adding the reagent cumulatively to the bath. Results T he phenylephrine-induced contractions were markedly lower, with no cha nge in the pD(2) values (i.e. the negative logarithm of the concentrat ion for half-maximal response), in cavernosal strips obtained from cas trated rabbits than in those from controls. Endothelium-dependent rela xation elicited by carbachol increased in the castrated group but the relaxation induced by sodium nitroprusside did not change and those el icited by adenosine were strongly depressed when compared with control s, There were no significant changes in the pD(2) values of agonist-in duced relaxation responses in all groups. The relaxation elicited by e lectrical-field stimulation at lower frequencies increased in strips f rom castrated rabbits but at higher frequencies were unchanged when co mpared with controls. Castration-induced changes in the relaxation res ponse of cavernosal strips were significantly restored by in vivo test osterone replacement but those induced by phenylephrine were not. Conc lusion The lack of testosterone has an effect on the reactivity of the corpus cavernosum, indicating that testosterone has an important role in erectile function by a pre- or post-synaptic action on the corpus cavernosum.