We aimed to investigate the effect of sulfhydryl (SH) inactivating agents, ethacrynic acid and N-ethylmaleimide, on the contractile activity of rat detrusor muscle. Wistar Kyoto rats weighing 150-250 g were anaesthetized with ketamine and bled to death. The urinary bladders were surgically removed and detrusor strips were mounted under 0.5 g tension in organ baths. The responses were recorded with isotonic transducers on polygraph paper. After an equilibrium period, the tissues were contracted by electrical field stimulation, acetylcholine, ethacrynic acid or N-ethylmaleimide and the effects of L-cysteine, glutathione, verapamil, Ca(2+)-free solution, sodium nitroprusside or atropine were then examined on these contractions. Verapamil, Ca(2+)-free solution or atropine significantly reduced the contractions elicited by electrical field stimulation and acetylcholine whereas L-cysteine, glutathione or sodium nitroprusside had no effect on the contractions in response to these stimuli. L-Cysteine, glutathione, verapamil or Ca(2+)-free solution significantly inhibited the contractions induced by ethacrynic acid or N-ethylmaleimide. Sodium nitroprusside slightly inhibited only the contraction induced by ethacrynic acid but not that with N-ethylmaleimide. Atropine has no action on the contractions in response to these SH reagents. These findings suggest that SH reagents may play a role in the contractile activity of rat detrusor muscle and this action seems to be related to the gating of Ca(2+) channels. Further experiments are needed to determine the cellular mechanism(s) of action by which these SH reagents act on the detrusor smooth muscle.