Effect of Skeletal Muscle Relaxants on Bladder Smooth Muscle

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Abstract
The effects of skeletal muscle relaxants on contractions of bladder smooth muscle were determined. Rat, rabbit and human bladder muscle strips were incubated in a 50 ml organ bath filled with physiological salt solution, aerated with 95% O, 5% CO2 and maintained at 37.degree. C. Contractions were induced both electrically and with acetylcholine. Contractile strength was measured before and after 30 to 70 min incubations with diazepam (0.25 to 1.0 .mu.g/ml), dantrolene sodium (4 .mu.g/ml) or baclofen (4 .mu.g/ml). Neither baclofen nor dantrolene sodium had any effect (P > 0.3) on electrically or acetylcholine-induced contractions in any of the 3 species tested but diazepam potentiated both electrically induced 115% of predrug contractile strength, P < 0.05) and acetylcholine-induced (122% of predrug contractile strength, P < 0.01) contractions of rat, but not rabbit or human, bladder muscle. In rabbits diazepam significantly reduced maximal bladder pressures in vivo (P < 0.05) but had no effect on bladder capacity. Dantrolene sodium had no effect on rabbit bladder pressure or capacity in vivo. While diazepam is thought to exert its effects on skeletal muscle through CNS inhibition these results suggest that diazepam may affect rat but not rabbit or human bladder smooth muscle directly.