SOME PREJUNCTIONAL AND POSTJUNCTIONAL EFFECTS OF CASTRATION IN RABBITISOLATED CORPUS CAVERNOSUM AND URETHRA

Pre- and postjunctional effects of castration were investigated in iso lated corpus cavernosum (CC) and prostatic and preprostatic urethral p reparations obtained from rabbits that had been castrated surgically 1 4 days before investigation. Preparations obtained from untreated anim als were used as controls. Castration did not change the relaxing effe cts of SIN-1 (NO donor) or papaverine in CC preparations contracted by noradrenaline (NA). Electrical field stimulation of CC preparations c ontracted by NA or endothelin-1 produced frequency-dependent and tetro do-toxin-sensitive relaxations. As compared with controls, the electri cally induced relaxations were increased in preparations from castrate d animals. Pretreatment with prazosin increased the electrically induc ed relaxations in CC from untreated rabbits, but had no effect on prep arations from castrated animals. In CC preparations incubated with H-3 -NA, castration significantly reduced the electrically evoked release of H-3. L-NOARG, an inhibitor of NO synthase, had no effect on H-3-eff lux. In prostatic, but not preprostatic, urethral preparations contrac ted by NA, the relaxant effects of SIN-1 and vasoactive intestinal pol ypeptide were significantly smaller following castration. Furthermore, castration significantly reduced electrically evoked relaxations in p rostatic urethral preparations contracted by NA, while in preprostatic urethra, no such effect was seen. Castration or L-NOARG had no effect on the electrically induced release of H-3-NA in either of the urethr al tissues. The results suggest that the hormonal changes caused by ca stration may modulate the functional effects in vitro of some parts of the urogenital tract. In penile erectile tissue, the relaxations indu ced by electrical field stimulation are increased, probably for the mo st part through a decrease in the neuronal release of NA. In prostatic urethra, on the other hand, electrically evoked relaxations are decre ased, possibly as a result of an impaired ability of the smooth muscle itself to respond to relaxant agents. In preprostatic urethra, castra tion has no obvious functional effects. The physiological consequences of these findings in the in vivo situation remain to be established.