Effects of adrenaline and noradrenaline on ear vessels in cold- and warm-adapted rabbits

¹ Department of Physiology, University of Kentucky, Lexington, Kentucky

Cold exposure increases the secretion of catecholamines and enhances the effect of these hormones on metabolism. Whether the sensitivity of peripheral vessels to adrenaline and noradrenaline is altered by cold exposure has not been reported. Warm-adapted (27 ± 1 C) and cold-adapted (5 ± 1 C) rabbits were studied under chloralose or urethan anesthesia. Adrenline and noradrenaline were infused (3 µg/kg/min) through an car vein. Colonic plus car temperature, ECG, blood flow, and venous pressure in the ear were measured. Compliance of ear veins was calculated from the V/P at pressures of 20 and 30 mm Hg. After prolonged cold exposure rabbits responded to catecholamine infusion (adrenaline and noradrenaline) with less change in heart rate during infusion and a more rapid return to control levels following infusion; with less decrease in ear temperature during infusion and a more rapid return to control levels following infusion, less increase in peripheral resistance, and less effect on compliance of the capacitance vessels (veins). The infusion caused a slight rise in colonic temperature in both groups.