Interaction of catecholamines and corticosteroids during the process of muscle fatigue

: After prolonged (8 hrs) swimming, the level of corticosteroids was reduced and the contents of aldosterone and DOC in the blood was increased in the rats. At incubation of these rats' adrenals in the L-thyrosine substratum the synthesis of adrenaline was reduced. Addition of hydrocortisone, prednisolone and corticosterone into the medium as well as in vivo administration of these increased the adrenaline synthesis in swimming rats and did not alter it in intact rats. Neither in vitro addition of aldosterone nor in vivo administration of ACTH activated the process. The activating effect of glucocorticoids was absent at incubation of the adrenals with L-DOPA and L-noradrenaline. Synthesis of cathecholamines in the heart of swimming rats in the presence of L-thyrosine and L-DOPA as precnrsors was suppressed; neither was it restored by administration of corticosteroids both in vitro and in vivo. This suggests that one of the reasons for suppression of the catecholamine synthesis in adrenals at obvious physical fatigue is the decrease of the glucocorticoid activity.