Glutathione deficiency and peripheral metabolism of thyroid hormones during dietary cysteine deprivation in rats

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Abstract
1. For a period of 24 d, young rats received a diet containing 120 g casein/kg or the same basic diet supplemented with 1·93 g cysteine/kg.2. The thyroxine (T4) turnover was decreased in rats receiving the cysteine-deficient diet compared with that of rats on the supplemented diet. Moreover, the extrathyroidal T4pool and T4disposal rate decreased.3. Cysteine deprivation also decreased the peripheral metabolism of 3,5,3'-triiodothyronine (T3). The T3distribution space, extrathyroidal pool of T3and T3disposal rate were diminished.4. In vitro, deiodination of T4in liver homogenate assayed with endogenous glutathione (GSH) demonstrated decreased T3production rates in the case of cysteine deficiency. This difference was minimized by the addition of GSH in amounts sufficient to saturate the reaction kinetics. In the light of this finding, GSH is probably involved in the promotion of certain thyroidal problems induced by a cysteine-deficient diet.