title: Influence of thyroid function on the in vivo cortisol in equilibrium cortisone equilibrium in man.
abstract: To evaluate the effect of thyroid function on the in vivo cortisol in equilibrium cortisone (F in equilibrium E) equilibrium, double-labeled cortisol tracer techniques were used to measure separately the rates of the F leads to E and E leads to F reactions in 4 euthyroid, 2 hypothyroid, and 2 hyperthyroid subjects. The rate of the F leads to E reaction was calculated from the appearance rate of 3H in body water after the i.v. injection of [11 alpha-3H]-cortisol; the rate of the E leads to F reaction was calculated from the difference in the plasma turn-over rates of [11 alpha-3H]-cortisol, and [4-14C]-cortisol after simultaneous i.v. injection of both tracers; the F in equilibrium E set-point was calculated by dividing the F leads to E rate by the E leads to F rate. In euthyroid subjects the F leads to E reaction rate averaged 1.6%/min, the E leads to F reaction rate averaged 1.0%/min, and the F in equilibrium E set-point averaged 1.6. In hyperthyroid subjects the two reaction rates were supranormal: the F leads to E rate averaged greater than or equal to 3.9%/min and the E leads to F rate averaged 1.54%/min; since the increase in the F leads to E rate was proportionally greater, the F in equilibrium E set-point (average greater than or equal to 2.6) was displaced towards cortisone. In hypothyroid subjects both reaction rates were equally slowed, to an average of 1.0%/min (F leads to E) and 0.68%/min (E leads to F); the F in equilibrium E set-point averaged 1.65, the same as in euthyroid subjects. Displacement of the F in equilibrium E equilibrium towards cortisone in hyperthyroid subjects appears to account for their elevated urinary THE/THF ratios, but the normal F in equilibrium E set-point in hypothyroid subjects makes it necessary to invoke a different mechanism for their depressed THE/THF ratio; it is suggested that increased conversion of THE to cortoic acids may be the responsible factor.
mesh_terms: D000328:Adult; D001834:Body Water / Q000378:metabolism; D002250:Carbon Radioisotopes; D003348:Cortisone / Q000378:metabolism*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D006980:Hyperthyroidism / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D009230:Myxedema / Q000378:metabolism*; D013961:Thyroid Gland / Q000502:physiology*; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D014316:Tritium; D003348:Cortisone; D006854:Hydrocortisone