Functional roles of cyclic AMP and cyclic GMP on rabbit urinary bladder and urethral smooth muscle contraction

: It is suggested that cyclic AMP and cyclic GMP play regulatory roles in smooth muscle function. In order to clarify the role of cyclic AMP and cyclic GMP in the function of the lower urinary tract, I examined the effects of isoproterenol and sodium nitroprusside on contractile force and tissue content of cyclic AMP and cyclic GMP. Isoproterenol (10(-8)-10(-4) M) caused a relaxing effect in the rabbit urinary bladder dome, the bladder base and the urethra. The relaxation response by isoproterenol was mediated by cyclic AMP. The relaxation response and the increase in the cyclic AMP level were marked in the bladder dome. Sodium nitroprusside (10(-8)-10(-4) M) also caused a relaxing effect in the rabbit urinary bladder dome, the bladder base and the urethra. The relaxation response to sodium nitroprusside was mediated by cyclic GMP. The relaxation response and the increase in the cyclic GMP level were marked in the urethra. The external addition of derivatives of cyclic AMP and cyclic GMP (dibutyryl cyclic AMP and 8-bromo cyclic GMP, 10(-8)-10(-3) M) also caused a relaxing effect in the bladder dome, the bladder base and the urethra. These results demonstrated that both cyclic AMP and cyclic GMP were related to relaxation of the rabbit lower urinary tract smooth muscle. It seems that cyclic AMP may be mainly related to relaxation of the bladder dome and cyclic GMP may be mainly related to relaxation of the urethra.