Effect of Chronic Treatment with Propranolol on the Cardiovascular Responses to Chronic Cold Exposure

Abstract Sun, Z., J. R. Cade, M. J. Fregly and N. E. Rowland. Effect of chronic treatment with propranolol on the cardiovascular responses to chronic cold exposure. Physiol Behav 62(2) 379–384, 1997.—The purpose of this study was to determine whether β -adrenergic receptors are involved in the elevation of blood pressure, tachycardia, and cardiac hypertrophy in rats chronically exposed to cold (5°C). Four groups of rats were used. Two groups of rats were exposed to 5°C and the other 2 groups were kept at 25°C. In each temperature condition, one group received regular food while the other received food to which a nonspecific β -adrenoceptor antagonist, d,l-propranolol, was added. The blood pressure of the untreated, cold-exposed group increased significantly within 3 weeks of exposure to cold and remained elevated until the end of the experiment. Chronic treatment with d,l-propranolol decreased the rate of cold-induced elevation of blood pressure at doses of 1.0 and 1.2 g/kg of food, and produced a complete reversal of hypertension at a higher dose (1.5 g/kg of food). Propranolol also prevented tachycardia in cold-exposed rats. The fact that propranolol decreased the elevation of blood pressure and prevented tachycardia suggests that both β 1 - and β 2 -adrenoceptors are blocked in cold-exposed rats. Propranolol, however, did not affect cold-induced cardiac hypertrophy.