Effects of thyroid hormones on ring A reduction cortisone by liver.

YATES, F. EUGENE,JOHN URQUHART AND ARTHUR L. HERBST.&"~~~S of thyroid hormones on ring A reduction of cortisone by liver. Am. J. Physiol. 195(g): 373-380. 1958.Triiodothyronine increases total hepatic capacity for in vitro reduction of ring A of cortisone by 38% in both male and female rats. Thyro-parathyroidectomy decreases it 56% in males and 48% in females. These alterations in thyroid state influence hepatic reduction of corticosteroids in several ways : a) the total amount of A4-steroid hydrogenases in the liver may be altered, both by changes in liver size and by changes in amount of enzyme per gram of liver; and, b) the activity per gram of liver can also be altered through variations in coenzyme (TPNH) availability. These effects of thyroid hormones provide an enzymatic basis for the alterations in biological half-life of adrenal steroids observed in hyperand hypothyroidism. A very close correlation (Y = 0.97) between total hepatic capacity to inactivate cortisone and the size of the adrenal glands was found. It is suggested that the rate of ring A reduction of corticosteroids by liver determines the rate of ACTH secretion in unstressed animals. I N SEVERAL SPECIES it has been shown that the rate of disappearance from plasma of administered adrenal cortical hormones is increased in hyperthyroid states and decreased in hypothyroid states (25). Since alterations of renal excretion of unmetabolized steroids are not sufficient to account for these changes in the half-life of the adrenal cortical hormones (3), it has been concluded that thyroid hormones increase the rate of inactivation of corticosteroids. The present study was undertaken to determine whether thyroid hormones affect the rate of hepatic reduction of ring A of adrenal steroids and, if so, whether a specific hormonal induction of the n4-steroid hydrogenases is involved.