EFFECT OF CYPROHEPTADINE ON EPISODIC ACTH AND CORTISOL SECRETION

To investigate the effect of cyproheptadine on ACTH and cortisol secre tion, we obtained blood samples at 10-min intervals for 24 h in six he althy volunteers under basal conditions and under treatment with 16 mg day(-1) cyproheptadine. Cyproheptadine caused significant decreases i n mean plasma ACTH and cortisol levels in 30% and 19% of samples, resp ectively, mainly in the afternoon and evening. Analysis of episodic ho rmone secretion by three different methods demonstrated that the drug did not modulate the frequency but lowered the amplitudes of ACTH and cortisol secretory episodes. ACTH and cortisol responses following ovi ne CRH injection at 20.00 h were unchanged. We conclude that in the af ternoon and evening central serotoninergic mechanisms influence the ac tivity of the hypothalamic-pituitary-adrenal axis at the hypothalamic level by modulating the amplitude of the secretory hormonal bursts, bu t do not influence the increase in ACTH and cortisol secretion in the morning.