In vitro studies on the pharmacological properties of diacetolol, the major metabolite of acebutolol in man.

The cardioselectivity and specificity of diacetolol, the major metabolite of the beta-adrenoceptor blocking drug acebutolol, was studied in the isolated right atrium of the guinea-pig and rat and the papillary muscle and trachea of the guinea-pig. The beta-adrenoceptor blocking potency of diacetolol is about ten times lower than that of acebutolol. Like acebutolol, diacetolol was a more effective isoprenaline antagonist in the heart than in the trachea, thus showing relative cardioselectivity. The high water solubility of diacetolol and acebutolol led to a much faster disappearance of the beta-blockade after washout than the blockade by the lipid soluble agents propranolol and penbutolol. Like acebutolol, diacetolol had a weak intrinsic sympathomimetic activity. Cardiac depressant effects, e.g. decrease of maximum upstroke velocity and duration of the action potential and reduction in force of contraction, occurred with concentrations 100-1000 times higher than those needed for beta-blockade, thus indicating relative specificity.