Involvement of protein synthesis in the action of glucocorticoids on the working capacity of adrenalectomized rats.

The administration of cortisol for 3 or 5 days increased the maximal duration of swimming under additional load, equal to 3% of body weight, in adrenalectomized but not in intact Wistar rats. The liver tryptophan oxygenase activity also increased. The blockade of RNA synthesis by actinomycin D excluded both results of cortisol administration. High doses of progesterone (25 or 75 mg/day) decreased the working capacity, rendering the action of cortisol on the working capacity of adrenalectomized rats insignificant. However, the antagonism between two hormones was not striking at the level of liver tryptophan oxygenase induction. The results suggest that the action of glucocorticoids on the working capacity is mediated by RNA and, further, by protein synthesis. The competition for glucocorticoid cytoplasmic receptors, to be found between glucocorticoids and a high level of progesterone, can disturb this mechanism. The synthesis of hepatic enzyme proteins is not responsible for the action of glucocorticoids on the working capacity.