Effects of β-adrenoceptor agonists and antagonists on thermoregulation in the cold in lean and obese Zucker rats

Abstract This experiment examines whether the thermoregulatory ability of obese Zucker rats is comparable to that of lean rats following treatment with β-adrenoceptor agonists and antagonists in a cold (− 8°C) environment. Half-maximal doses of the nonselective β-adrenoceptor agonist isoproterenol (ISO) produced net thermolytic (heat loss) effects in both obese and lean rats in an operant lever pressing for radiant heat task. ISO increased the demand for heat, but posttest colonic temperature ( T c ) decreased. A low dose of propranolol (100 μg/kg) normalized thermoregulatory behavior, T c , and thermal balance when coadministered with ISO. Activation of thermogenesis with the selective β 3 -agonist BRL 35135 (BRL) reduced heat influx by both obese and lean rats at doses between 2 and 10 μg/kg, but no dose-response effects were evident within this range. Posttest T c and thermal balance indicated no thermolytic effects. No evidence was found for a β 2 -component in the BRL response when a supramaximal dose (40 μg/kg) was tested with the selective β 2 -antagonist ICI 118551 (1 mg/kg). These data show that, despite a higher baseline demand for heat, the obese Zucker rat responds to the thermogenic effects of BRL and the thermolytic effects of ISO as does the lean rat.