Increased α2‐ but similar β‐adrenergic receptor activities in subcutaneous gluteal adipocytes from females compared with males

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Abstract
.alpha.- and .beta.-adrenergic binding and action were studied in subcutaneous adipocytes from the gluteal region in females and males. The .beta.-selective antagonist [3H]dihydroalprenolol and the .alpha.2-selective antagonist [3H]yohimbine were used to identify the .beta.- and the .alpha.2-receptor, respectively. The biological effects mediated by these receptors were determined by measuring the glycerol release induced by isoproterenol (.beta.-receptor agonist) and by clonidine (.alpha.2-receptor agonist). The study consisted of health volunteers (eighteen females and fifteen males). Compared to men the .alpha.2-receptor binding was increased by 73% (P < 0.01) in adipocytes from females. From Scatchard analysis it was determined that the increased binding was due to an increased receptor number (438 v. 262 fmol mg-1 protein, P < 0.001) with unaltered Kd (1.18 v. 1.35 nmol l-1, P > 0.05). This increased .alpha.2-receptor binding in female and adipocytes was associated with a significantly increased sensitivity (P < 0.05) and maximal antilipolytic effect of clonidine (P < 0.05). The .beta.-receptor binding was similar in adipocytes from females and males. However, isoproterenol was significantly more lipolytic in female adipocytes (P < 0.01). Since the combination of theophylline and adenosine deaminase also was significantly more lipolytic in female adipocytes the enhanced effects of isoproterenol then seemed to be due to mechanisms not directly related to the hormone-.beta.-receptor binding. Finally, the mixed .beta.- and .alpha.2-receptor agonist, adrenaline showed biphasic effects on lipolysis, with stimulatory effect at low concentrations (< 500 nmol l-1) and pronounced inhibitory effect at higher concentrations (< 1 .mu.mol l-1). However, at low concentrations of adrenaline the lipolytic effect was significantly reduced in female gluteal adipocytes (P < 0.05), whereas the inhibitory effect was similar between females and males. It is concluded that female gluteal adipocytes possessed more .alpha.2-adrenergic receptors than male adipocytes. This increased binding was accompanied by enhanced antilipolytic effect of clonidine and reduced lipolytic effect of low concentrations of adrenaline. Thus, it is suggested that the increased .alpha.2-receptors in female gluteal adipocytes might be related to the enhanced tendency for females to accumulate fat in this region.

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