This study was undertaken in order to test the hypothesis that selective β3-AR stimulation and simultaneous blockade of α2-AR would result in an increase of lipolysis and thermogenesis in rats. Incubation of isolated white adipocytes with the α2-AR antagonist yohimbine produced a concentration-dependent increase in glycerol release (P<0.001) for all assayed concentrations (10-12-10-6 M) and potentiated the lipolytic effect of the β3-AR agonist Trecadrine. However, in vivo administration of yohimbine produced a marked decrease in body temperature (1.3-1.5°C, P<0.001) and blocked the thermogenic effect of Trecadrine when simultaneously administered. A similar response was observed for whole body oxygen consumption. Furthermore, yohimbine did not modify brown adipose tissue oxygen consumption, but blocked the β3-AR-mediated increase triggered by Trecadrine. Brown adipose tissue UCP-2 and -3 mRNA expression was not changed by yohimbine. In conclusion, the present work indicates that in vitro α2-AR blockade by yohimbine potentiates the β3-AR-mediated stimulation of lipolysis. On the other hand, in vivo α2-AR antagonism blocks the thermogenic effects mediated by β3-AR stimulation, suggesting a possible interplay between the receptors.

Related Articles