Alpha‐adrenergic antilipolytic effect of adrenaline in human fat cells of the thigh: comparison with adrenaline responsiveness of different fat deposits

Abstract. The present results show that isolated fat cells from the subcutaneous adipose tissue of the lateral part of the thigh exhibit resistance to adrenaline. However, inability of adrenaline to induce lipolysis is not linked to a β‐receptor defect since a β‐adrenoceptor‐stimulating agent (isoproterenol) exerts a clear lipid mobilizing effect. The blocking of α‐adrenoceptors by phentolamine (an α‐adrenoblocking drug) unmasks the strong lipolytic effect of adrenaline. Moreover, our investigation demonstrates the occurrence of an inhibiting effect of adrenaline on theophylline‐induced lipolysis. This inhibitory effect is suppressed by phentolamine and strengthened by propranolol (β‐adrenoblocking drug). Thus it seems that one of the important facts able to explain adrenaline resistance of the adipocytes from the subcutaneous adipose tissue of the thigh could be increased alpha‐adrenergic responsiveness initiated by mixed agonists such as adrenaline or noradrenaline. Moreover, our data demonstrate that the differences in the lipolytic responses to adrenaline between isolated fat cells taken from different sites could be linked to a variable α‐adrenergic‐inhibiting effect rather than a modified β‐adrenergic effect. In conclusion, the balance between the two receptor site activities could be different according to the anatomical localization of the fat deposits, thus explaining the differences in adrenaline responsiveness reported in this paper.