Effect of glucocorticoids on catecholamine synthesis in the adrenals and heart of rats during physical fatigue

Abstract

The effect of adrenocortical hormones on catecholamine synthesis in the adrenals and heart of rats was studied after prolonged swimming (8 h). Catecholamine synthesis during incubation of the adrenals with L-tyrosine was sharply depressed after swimming. Addition of hydrocortisone or prednisolone in vitro (50 μg per sample) and also injection of these hormones in vivo (50 mg/kg intramuscularly, 3 h before decapitation) increased catecholamine synthesis in the adrenals of the swimming rats but not of intact rats. On incubation of the adrenals of swimming rats in the presence of L-dopa and L-noradrenalin catecholamine synthesis was reduced compared with that in intact animals and was not restored on the addition of glucocorticoids. No stimulating effect of aldosterone on catecholamine synthesis in the adrenals could be detected in the presence of L-tyrosine. On incubation of the heart tissue of swimming rats in the presence of L-tyrosine and L-dopa, catecholamine synthesis was depressed and was not restored by glucocorticoids invitro or in vivo. It is concluded that glucocorticoids can restore catecholamine synthesis when depressed by intensive physical fatigue by acting on the tyrosine hydroxylase stage.