Catecholamine-induced adipocyte lipolysis in human hyperthyroidism.

Increased lipid mobilization in thyrotoxicosis is attributed to amplification of catecholamine action in fat cells by thyroid hormones. We investigated the adrenergic regulation of lipolysis in isolated sc abdominal fat cells obtained from 14 patients with thyrotoxicosis and 18 control subjects. Ten of the hyperthyroid subjects were also reinvestigated after antithyroid treatment. The thyrotoxic state was associated with a 3-fold increase in maximum norepinephrine-induced lipolysis (P < 0.005), unaltered sensitivity to dobutamine (selective β1-adrenoceptor agonist) and clonidine (selective α2-adrenoceptor agonist), but 15 times enhanced sensitivity to terbutaline (selectiveβ 2-adrenoceptor agonist; P < 0.01). Moreover, thyrotoxicosis was accompanied by a 3-fold increase inβ 2-adrenoceptor number (P < 0.005), but unchanged β1-adrenoceptor levels. Further, the lipolytic effects of dibutyryl cAMP (activating protein kinase A and thereby hormone-sensitive lipase) and forskolin (activating adenylate cyclase) w...