The influence of hyperthyroidism and hypothyroidism on the beta-adrenergic responsiveness of the turkey erythrocyte.
The mechanisms responsible for altered adrenergic tone in hyperthyroidism and hypothyroidism are not fully understood. To investigate these mechanisms, the beta-adrenergic receptor-cyclic AMP complex of the turkey erythrocyte was studied among groups of normal, hyperthyroid, and hypothyroid turkeys. In erythrocytes obtained from hypothyroid turkeys, there were fewer beta-adrenergic receptors than in normal cells as determined by the specific binding of [(125)I]iodohydroxybenzylpindolol, as well as associated decreases both in catecholamine-responsive adenylate cyclase activity and in cellular cyclic AMP content. In contrast, erythrocytes obtained from hyperthyroid turkeys contained the same number of beta-receptors and had the same catecholamine-responsive adenylate cyclase activity as cells from normal birds. Other characteristics of the beta-receptors in cells from hyperthyroid birds were indistinguishable from those present in normal erythrocytes. However, within the range of circulating catecholamine concentrations, 5-50 nM, the erythrocytes of the hyperthyroid turkeys generated substantially more cyclic AMP after exposure to isoproterenol than did normal cells. These results suggest that thyroid hormone affects beta-receptor-cyclic AMP interrelationships in the turkey erythrocyte by two distinct mechanisms: (a) In hypothyroidism, both beta-receptors and catecholamine-dependent cyclic AMP formation are coordinately decreased; (b) in hyperthyroidism, beta-receptors are unchanged but there is an amplification of the hormonal signal so that occupation of a given number of receptors at physiological concentrations of catecholamines leads to increased levels of cyclic AMP.
D000262:Adenylyl Cyclases / Q000097:blood; D000818:Animals; D002395:Catecholamines / Q000097:blood; D000242:Cyclic AMP / Q000097:blood; D004912:Erythrocytes / Q000378:metabolism*; D006980:Hyperthyroidism / Q000097:blood*; D007037:Hypothyroidism / Q000097:blood*; D010869:Pindolol / Q000031:analogs & derivatives / Q000097:blood; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014422:Turkeys
D002395:Catecholamines; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D014284:Triiodothyronine; D010869:Pindolol; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D013974:Thyroxine