Inhibitory effect of sodium nitroprusside on the relaxing action of isoproterenol in isolated rat urinary bladder

Abstract 1. Isoproterenol caused relaxation of rat detrusor muscles contracted by electrical stimulations. Sodium nitroprusside (SNP) and methylene blue inhibited the relaxation induced by isoproterenol without affecting forskolin-induced relaxation. 2. In the presence of theophylline, zaprinast still potentiated isoproterenol-relaxation. In the presence of butoxamine, a selective β 2 -adrenoceptor inhibitor, but not metoprolol, a selective β 1 -adrenoceptor inhibitor, SNP still inhibited isoproterenol-relaxation. 3. SNP inhibited the relaxation to dobutamine, a β 1 -adrenoceptor agonist, but not that to terbutaline, a β 2 -adrenoceptor agonist. The relaxation to dobutamine was also inhibited by methylene blue. Further, in the presence of theophylline, zaprinast still potentiated dobutamine-relaxation. 4. Isoproterenol increased tissue level of cGMP, which was inhibited by propranolol. 5. These results suggest a possibility that, in rat detrusor muscles, isoproterenol causes relaxation due to increases in the level of both cAMP and cGMP.