HETEROGENOUS ACTIVITY OF BRL-35135, A BETA(3)-ADRENOCEPTOR AGONIST, IN THERMOGENESIS AND INCREASED BLOOD-FLOW IN BROWN ADIPOSE-TISSUE IN ANESTHETIZED RATS

1. The effects of BRL 35135, a beta(3)-adrenergic agonist, on body tem perature and regional blood flow in brown adipose tissue (BAT) were si multaneously recorded in anaesthetized rats and compared to isoprotere nol. 2. BRL 35135 at doses of 0.1 and 1 mu g/kg (i.v.) induced dose-de pendent increases in BAT temperature with minimal effects on systemic diastolic blood pressure (DBP), heart rate (HR) and BAT blood flow. 3. The thermogenic effect of BRL 35135 at a dose of 10 mu g/kg (i.v.) wa s smaller than that at a dose of 1 mu g/kg, and was accompanied by a m arked increase in BAT blood flow. 4. Isoproterenol at doses of 0.01-1 mu g/kg (i.v.) dose-dependently increased HR and BAT blood flow and de creased DBP. It did not affect BAT temperature. 5. These findings indi cate that unlike isoproterenol, BRL 35135, at the lower doses, selecti vely causes thermogenesis in BAT which was detectable as changes in BA T temperature, and that the vasodilator effect in BAT is not as sensit ive as the thermogenic effect of beta(3)-adrenergic agonists.