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

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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. pA<SUB>2</SUB> 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.
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