Relationship between plasma corticosterone and adrenal epinephrine after diazepam treatment in rats

Following recent observations that diazepam treatment increases adrenal epinephrine in rats, we were interested in studying the possible mechanisms of this action of diazepam on rat adrenal glands. All diazepam treatments studied (1-25 mg . kg-1.day-1 for 10 days) led to an increase in adrenal epinephrine following a linear dose-effect relationship. Since epinephrine synthesis is under neuronal and humoral controls, we investigated their respective importance in the effect of diazepam on the adrenal gland. The denervation of the adrenal gland did not prevent the increase in adrenal epinephrine by diazepam treatment. On the hand, diazepam treatment was shown to cause an increase in plasma corticosterone in parallel with an increase in adrenal epinephrine. Administration of dexamethasone (a synthetic corticoid) and hypophysectomy prevented the increase in adrenal epinephrine and plasma corticosterone resulting from diazepam treatment. We thus conclude that the increase in adrenal epinephrine seen after diazepam treatment is parallel to the increase in plasma corticosterone. Moreover, since the action of diazepam on adrenal epinephrine is prevented by dexamethasone or hypophysectomy, we hypothesize that diazepam is acting on the adrenal cortex via the release of adrenocorticotropic hormone (ACTH). ACTH and corticosterone would be responsible for the increased activity of epinephrine-synthesizing enzymes in adrenal medulla.