Pineal-adrenal interactions: the effect of acute pharmacological blockade of nocturnal melatonin secretion.

The pineal gland is a complex neuroendocrine organ which is under photoneuroendocrine control. Previous studies in animals and humans have suggested reciprocal variations in pineal melatonin biosynthesis and adrenal glucocorticoid output; it remains unclear, however, whether a causal relationship exists between these two systems. To address this question, we examined the overnight secretory activity of the hypothalamic-pituitary-adrenal (HPA) axis in conjunction with acute pharmacological suppression of pineal melatonin biosynthesis in 11 healthy volunteers. Results of the current study are consistent with the hypothesis that melatonin does not function as a tonic inhibitor of the HPA axis on an acute basis.