Effects of beta-adrenoceptor blocking agents on isolated atrial and papillary muscles from experimentally diabetic rats.

Effects of propranolol and atenolol on isoproterenol-induced responses of isolated atrial and papillary muscles from experimentally diabetic rats were examined. Male Sprague-Dawley rats were divided into the diabetic group (DM) which received streptozotocin 60 mg/kg, i.v. and the control group (C) which received vehicle i.v. At 6 weeks after, the right atrial or right ventricular papillary muscle was isolated, and the beating rate (R) in the atrium or isometric force development (F) and its first derivatives (+/- dF/dt) in the papillary muscle under pacing were recorded. Basal R was less frequent in DM than in C, but ED50 values for isoproterenol-induced chronotropy were not different between the two groups. Basal F and basal +/- dF/dt were not different between the two groups, but isoproterenol-induced increases in F and +/- dF/dt were less in DM than in C. ED50 values in F and +dF/dt were not different between the two groups. Propranolol and atenolol shifted the concentration-response curves in R, F and +/- dF/dt for isoproterenol to the right in both groups. pA2 values of propranolol and atenolol for each parameter were not different between the two groups. Results indicate that propranolol and atenolol exert the same beta-adrenoceptor blocking potency in both diabetic and non-diabetic hearts of rats.