EFFECTS OF STIMULATORY AND INHIBITORY THYROTROPIN RECEPTOR ANTIBODIES ON LIPOLYSIS IN INFANT ADIPOCYTES

TSH is a potent lipolytic hormone for isolated human adipocytes from neonatal subjects. Crude immunoglobulin fractions from sera of patients with Graves' disease, containing stimulatory TSH receptor (TSHR) autoantibodies, significantly increased lipolysis in fat cells from infants, whereas immunoglobulin fraction from a patient with inhibitory TSHR autoantibodies (TBab) blocked TSH-induced lipolysis in a dose-dependent manner. Although TBab, totally blocked the maximum lipolysis induced by TSH (10(5) mU/L), no effect was seen on isoprenaline-induced lipolysis. The maximum lipolytic response to TSH was similar to that seen with the beta-adrenoceptor agonist isoprenaline, and there was a similar cAMP increase in response to both stimulators. From these results, it is concluded that the TSHR in infant adipocytes is likely to be coupled to the adenylate cyclase system, and the lipolytic effect of TSH can be simulated by stimulatory TSHR autoantibodies or inhibited by TBab.