Fat cell β-adrenergic receptor in the hypothyroid rat. Impaired interaction with the stimulatory regulatory component of adenylate cyclase

Fat cells from the hypothyroid rat fail to synthesize cyclic AMP in response to β-adrenergic agonists, although possessing normal amounts of β-adrenergic receptors (R) and catalytic adenylate cyclase activity. Membranes of hypothyroid rat fat cells contain M(r) = 42,000 (major form), 46,000, and 48,000 (minor forms) peptides of the stimulatory guanine nucleotide-binding regulatory component (N(s)) radiolabeled in the presence of cholera toxin and [³²P]NAD⁺. Maps of fragments generated by partial proteolysis of these radiolabeled peptides are virtually identical in hypothyroid and euthyroid preparations. Two-dimensional gel electrophoresis showed that the size and charge of the M(r) = 42,000, 46,000, and 48,000 radiolabeled peptides are similar in euthyroid and hypothyroid rat fat cell membranes. Extracts of hypothyroid rat fat cell membranes express normal amounts of N(s) activity as measured by their ability to reconstitute the adenylate cyclase of membranes of S49 mouse lymphoma cyc^- mutant cells which lack functional N(s) activity. Hybridization of hypothyroid rat fat cells with donor membranes of normal rat fat cells, rat hepatocytes, or S49 cyc^- cells restores the β-adrenergic response of these fat cells. Pretreating the donor membranes with a β-adrenergic antagonist covalent label blocks the ability of these membranes to restore the response of the cells. Rat hepatocytes pretreated with a β-adrenergic antagonist covalent label do not accumulate cyclic AMP in response to isoproterenol. Hybridization of these receptor-deficient hepatocytes with fat cell ghosts of euthyroid rats restores β-adrenergic stimulation of cyclic AMP accumulation, whereas hybridization with fat cell ghosts of hypothyroid rat does not restore this response. N(s) of pigeon erythrocyte membranes radiolabeled with cholera toxin and [³²P]NAD⁺, extracted in cholate, and reconstituted with fat cell membranes interacts with fat cell R. The ability of R to interact with N(s) of pigeon erythrocyte membranes is impaired when the reconstitution is performed with membranes from the hypothyroid rat fat cell. Hypothyroidism appears to affect the ability of R to interact productively with N(s), without affecting either R number or N(s) structure and function.