[Inhibitory effect of a calcium entry blocker (verapamil) on detrusor muscle contractility: feasibility of clinical application].

Effects of a Ca2+ entry blocker (verapamil) on the contractility of the bladder detrusor muscle of rabbits were investigated in vitro and in vivo. In experiments using smooth muscle strips from the bladder detrusor, isometric tension changes of the strips following drug addition were recorded. The contractions of the strips induced by acetylcholine (10(-8)-10(-2)M), prostaglandin E2, F2-alpha (3 X 10(-8)-3 X 10(-5)M) or electric stimulation were significantly inhibited dose-dependently by pretreatment of the strips with verapamil (10(-7), 10(-6)M). In in vitro experiments using whole bladder preparations, the spontaneous contractile activity and the contraction induced by acetylcholine (10(-6)M) were monitored. Both activities were inhibited in a time-dependent manner after the intravesical instillation of 7.5 mg verapamil. The amplitude of the spontaneous contraction and responses to acetylcholine, 90 minutes after the instillation, were reduced to 10% and 38% of the control levels (before the instillation), respectively. The detrusor contractility was still inhibited 2 hours after the removal of verapamil from the bladder. During in vivo experiments, changes in intravesical pressure and systemic arterial pressure were monitored. Sixty minutes after the intravesical instillation of 10 mg verapamil, the rise of the intravesical pressure following the pelvic nerve stimulation was inhibited to 18% of the control level, whereas the systemic arterial pressure was not affected. Verapamil is suggested to have potent inhibitory effects on the detrusor muscle contraction, and the intravesical instillation of verapamil to inhibit detrusor contractility without affecting the cardiovascular status.