Effect of various drugs on the binding of thyrotrophin to thyroid plasma membranes.

Effects of enzyme inhibitors and membrane-active drugs on the binding of 125I-labelled thyroid-stimulating hormone (TSH) to human thyroid membranes and membrane adenylate cyclase (AC) activity were studied. FOY, a synthetic polyvalent proteolytic enzyme inhibitor, Trasylol, alpha- and beta-adrenergic blocking agents, tranquilizers, anti-histamines and polyene antibiotics enchanced TSH binding in a dose-dependent manner, whereas selective enzyme inhibitors and adrenergic stimulating agents had no effect. Both propranolol and FOY inhibited basal and TSH stimulated AC activity of thyroid membranes. FOY, as well as propranolol was found to have protective effects on hypotonic erythrocyte lysis. These results suggest that propranolol and FOY increased TSH binding by the same mechanism, probably the so-called membrane-stabilizing effects. Although the detailed mechanisms underlying the increased TSH binding by these drugs remain unknown, they may change the membrane structure, thereby enhancing the TSH receptor affinity.