Regulation of proteins by thyroid hormone and glucocorticoid: the responses of hepatic alpha 2U-globulin and pituitary growth hormone differ in adult male hypothyroid rats.
To investigate the possibility that a common phenomenon might exist by which glucocorticoids influence responses to thyroid hormones, the cytosol levels of four proteins were measured after 2 days of treatment with L-T3 (T3; 50 micrograms/100 g. day 2) and/or cortisone (2 mg/100 g./day) in adult male hypothyroid rats. Pituitary GH was measured by an established RIA. Hepatic alpha 2U-globulin, a hepatic protein whose synthesis is dependent on androgens thyroid hormones, glucocorticoids, and GH, was measured by a newly devised RIA shown to be sensitive and specific for alpha 2U-globulin. Hepatic malic enzyme and tyrosine aminotransferase were measured by enzyme assay. T3 stimulated pituitary GH, hepatic alpha 2U-globulin, and hepatic malic enzyme, but not hepatic tyrosine aminotransferase. Cortisone stimulated pituitary GH, hepatic alpha 2U-globulin, and hepatic tyrosine aminotransferase, but not hepatic malic enzyme. The response to T3 and cortisone in combination was equal to or greater than the sum of the responses to each hormone for hepatic alpha 2U-globulin and pituitary GH, but not for hepatic malic enzyme and tyrosine aminotransferase. The responses of pituitary GH to each treatment expressed as a ratio to hypothyroid control +/- SEM were: saline, 1 +/- 0.4; T3, 85.2 +/ 2.7; cortisone, 16.9 +/- 2.3; and T3 plus cortisone 133.9 +/- 5.4. The responses of hepatic alpha 2U-globulin were: saline, 1 +/- 0.6; T3, 6.6 +/-0.5; cortisone, 14.3 +/- 3.0; and T3 plus cortisone, 26.8 +/- 3.0. These results showed cortisone to have varying effects on thyroid hormone-responsive proteins in hypothyroid rats. Although both pituitary GH and hepatic alpha 2U-globulin were simulated in an additive manner, T3 alone was a more potent stimulus of GH, whereas cortisone alone was a more potent stimulus of alpha 2U-globulin.