Enzymatic changes in rat thymus after intraperitoneal injections of adrenocorticotrophic hormone and corticosterone

Intraperitoneal injection in adult male rats with adrenocorticotrophic hormone (ACTH) (0.6 mU daily for 3 days) brought about a marked decrease in the activities of four thymic enzymes studied: glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, isocitric dehydrogenase, malic dehydrogenase. A prominent rise in the levels of these enzymes occurred when ACTH was replaced by corticosterone (1 mg injected daily for 3 days). In adrenalectomized rats, the results were similar to those observed in intact animals. The significance of an increase in transaminase activities after corticosterone treatment, relating to an increase in citric cycle enzymes is discussed. On the other hand, it was suggested that ACTH exerts an extra adrenal effect on the thymus.