Effects of ethanol and its metabolite acetaldehyde on responses of the ratbladder

Objective To investigate the pharmacological effects of ethanol and its met abolite acetaldehyde on isolated rat bladder muscle, and thus assess the po tential influence of ethanol ingestion on the risk of urinary retention in patients with benign prostatic hyperplasia, Materials and methods Isometric tension changes of isolated rat bladder mus cle strips were recorded in an organ bath using a pressure transducer. The acute or prolonged effects of ethanol (1-4%) or acetaldehyde (0.01, 0.1 or 1 mmol/L) were assessed on resting tension, electrical field stimulation (E FS), and bethanechol- (0.5 mmol/L), ATP- (2 mmol/L) or KCl-(127 mmol/L) ind uced contraction. To determine the mechanism of acetaldehyde-induced stimul ation, an antihistamine, diphenhydramine was used after bethanechol stimula tion. Results At the concentrations used, ethanol and acetaldehyde did not change the pH of the bathing medium. The resting tension of the muscle was not ch anged by ethanol, and acetaldehyde caused only a small increase in baseline tone at 1 mmol/L. Incubation with ethanol or acetaldehyde significantly su ppressed contractility induced by EFS, bethanechol, ATP or KCl at each conc entration (P < 0.05). Contractions induced by all drugs were not changed si gnificantly by the acute application of ethanol and the acute application o f acetaldehyde did not affect contractions induced by ATP or KCl. However. EFS- or bethanechol-induced contractions were significantly enhanced (P < 0 .05). The acetaldehyde-induced effects were completely blocked by the H1 an tagonist, diphenhydramine (10 mu mol/L). Conclusions Ethanol did not affect resting tension but acetaldehyde and eth anol suppressed bladder muscle contractions. However, direct acetaldehyde-s timulation may release histamine and enhance contractility, This suggests t hat chronic alcoholism rather than acute intoxication is more likely to pro voke urinary retention.