Predominance of beta 3-adrenergic component in catecholamine activation of lipolysis in garden dormouse adipocytes.

The beta 3-adrenoceptor (AR) agonists are potent activators of lipolysis in white adipose tissue. beta-AR agonists were tested here on the lipolytic activity of a hibernator, the garden dormouse (Eliomys quercinus L.). All the agonists exhibited full intrinsic activity; the most potent was the beta 3-AR agonist BRL-37344 [half-maximal effective concentration (EC50) = 0.8 nM]. The beta-antagonist idocyanopindolol (ICYP) also stimulated lipolysis of white adipocytes with the same potency and intrinsic activity as BRL-37344. The blockade of lipolytic effects of epinephrine or norepinephrine was similar to that of BRL-37344: the beta 1- and the beta 2-antagonists were quite ineffective. Total blockade occurred only with 100 microM bupranolol whatever the beta-agonist tested. This argues for the presence of a beta 3-component in the adrenergic-induced lipolysis. (-)-[125I]ICYP and (-)-[3H]CGP-12177 both labeled two populations of binding sites. On adipocyte membranes, binding of 0.6 nM (-)-[3H]CGP-12177 was inhibited with the following order of potency: isoproterenol > BRL-37344 > epinephrine. This order was modified at 20 nM, arguing for the beta-atypical nature of the low-affinity sites. Thus garden dormouse adipocytes possess beta 3-ARs, which are involved to an important degree in the adrenergic activation of lipolysis.