Release of thyrotropin receptor from thyroid plasma membranes: effect of hydrocortisone, propranolol, and adenosine 3',5'-monophosphate.
Soluble TSH receptors were released into the medium when bovine thyroid plasma membranes were incubated in 0.01 M Tris-HCl, pH 7.5, at 0 or 20 C. This is a conventional hypotonic medium used in binding assays. The characteristics of binding of bovine [125I]TSH to the released TSH receptor were almost the same as those of binding to TSH receptors solubilized by lithium 3,5-diiodosalicylate or to the original plasma membrane. Released TSH receptor had two binding sites with Ka values of 0.7 x 10(10) and 0.1 x 10(8) M-1. T3, T4, KI, methimazole, and propylthiouracil had no effect on spontaneous TSH receptor release or on bovine [125I]TSH binding to solubilized TSH receptor. Hydrocortisone (10(-5)--10(-3) M) and d,l-propranolol (10(-3) M) inhibited receptor release. cAMP increased the release of TSH receptor. Hydrocortisone, d,l-propranolol, and cAMP had no effect on bovine [125I]TSH binding to solubilized or released TSH receptor. d,l-Propranolol and hydrocortisone may act as membrane-stabilizing agents. cAMP stimulation of release suggests that the release mechanism could depend upon a protein kinase-phosphoprotein system. Although these studies were conducted with membranes in an unphysiological medium, receptor release may occur normally and could be a source of circulating antigen related to production of antireceptor antibody in autoimmune thyroid diseases. Release of receptors during incubation in vitro may affect the results of studies of hormone-receptor interaction.
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D006854:Hydrocortisone / Q000494:pharmacology*; D007700:Kinetics; D011433:Propranolol / Q000494:pharmacology*; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*
D011956:Receptors, Cell Surface; D013972:Thyrotropin; D011433:Propranolol; D000242:Cyclic AMP; D006854:Hydrocortisone