Alpha 2- and beta-adrenergic receptor binding and action in gluteal adipocytes from patients with hypothyroidism and...

The alpha 2- and beta-adrenergic receptor activities have been investigated in human adipocytes in relation to thyroid status. Adipocytes from 11 hypothyroid and 18 hyperthyroid were compared with 19 euthyroid (normal) subjects. The lipolytic and cAMP responses to isoproterenol and epinephrine were greatly enhanced in adipocytes from hyperthyroid subjects (P less than .01) and impaired in adipocytes from hypothyroid subjects (P less than .05). However, the antilipolytic effect of clonidine (alpha 2-agonist) and the effect of clonidine on cAMP were similar in all three groups. The alpha 2- and beta-receptor numbers were both slightly increased in hyperthyroidism, but the ratio between the alpha 2- and beta-receptors was unchanged in relation to normal subjects. On the other hand, the adrenergic binding to adipocyte membranes from hypothyroid subjects was reduced, and the beta-receptor binding was reduced even much more (50%) than the alpha 2-receptor binding (20%, P less than .01). Thus, the alpha 2- and beta-receptor ratio was almost doubled in hypothyroid adipocytes (P less than .01). The antagonist affinity against the adrenergic receptors (determined by propranolol and yohimbine, respectively) was unchanged in the three groups. Agonist binding determined in intact adipocytes revealed unaltered affinity of clonidine for the alpha 2-receptor in the three groups. In hyperthyroidism, though, there was enhanced affinity of isoproterenol in competition with the beta-receptor (P less than .05). It is concluded that the inhibitory alpha 2-receptor pathway functions normally in all groups, indicating that the alpha 2-receptors and the alpha 2-receptor-mediated pathway in human adipocytes are relatively unaffected by thyroid hormones.(ABSTRACT TRUNCATED AT 250 WORDS)