IN-VIVO BETA-ADRENERGIC INDUCTION OF THE UNMASKING OF THE UNCOUPLING PROTEIN IN RAT BROWN FAT

1. In 28-degrees-C adapted rats (WA) both cold stress and norepinephri ne (NE) led to a 4-fold increase of uncoupling protein dependent proto n conductance which was abolished by propranolol (PRO). 2. In 4-day wa rm re-exposed rats (after 10 days at 5-degrees-C) (WR) the same uncoup ling by cold stress was observed but the NE effect was lower. Uncoupli ng by cold stress was not abolished by PRO. 3. In WR rats, uncoupling was not due to the involvement of an alpha-adrenergic pathway. 4. Both beta-agonist isoproterenol and beta3-agonists BRL 35135A and ICI D711 4 led to high levels of unmasking. 5. Interscapular brown adipose tiss ue surgical denervation, which abolished cold stress unmasking both in WA and WR rats, indicates a mediation by direct sympathetic innervati on. 6. Depending on the thermal history of the rat, the possibility th at unmasking by cold stress could be mediated by different types of be ta-receptors is discussed.