Effects of age and sex on the induction by triiodothyronine of cortisone delta4-5alpha-reductase and glucose 6-phosphate dehydrogenase of rat liver and adrenal

The effects of age and sex on the induction by 3,5,3′-triiodothyronine (T-3) of cortisone Δ⁴-5α-reductase and glucose 6-phosphate dehydrogenase (G 6-P D) in liver and the latter in adrenal have been investigated. Levels of cortisone Δ⁴-(5α, 5β)-reductase and G 6-P D were measured in homogenates of tissue from normal and T-3 injected male and female rats, $\text{1 1}\text{4}$ to 21 months of age. Increases in the levels of the reductase seen under T-3 stimulation were ascribed to induction of the 5α-reductase alone. T-3 caused induction of cortisone Δ⁴-5α-reductase only in the livers of male rats $\text{1}\text{3}\text{4}$ months of age. There was induction of total G 6-P D at most ages except in the livers of old male and young female rats and adrenals of young and old male rats. At all ages in normal animals of both sexes the maximum activity of glucose 6-phosphate dehydrogenase was much greater than that of cortisone Δ⁴-(5α, 5β)-reductase. It is concluded that the amount of G 6-P D in normal liver may be sufficient to handle an increase in cortisone reduction, and factors other than cortisone Δ⁴-reductase or G 6-P D levels alone must regulate increased reduction of the steroid.