Chrononeuroendocrine perspectives of ACTH and related peptides

The mechanism of the circadian hormonal secretions is still obscure. The cyclic activity of the hypothalamus-ACTH-adrenal (H-A-A) axis is perhaps the most studied. ACTH derives with other peptides from a common precursor, proopiomelanocortin. ACTH secretion is under inhibitory and stimulatory influences. The inhibitory influence is mediated by the negative feed-back of adrenal corticosteroids and by the short loop feed-back of ACTH on its own secretion. The stimulatory influence is exerted by the hypothalamic corticotropin releasing factor (CRF), recently isolated in the ovine hypothalamus. CRF is regulated by various neurotransmitttttorial activities. Serotonin and acetylcholine play a stimulatory role, while dopamine and norepinephrine, in particular, seem to exert an inhibitory tonic control. The increased ACTH secretion in stress-response seems to be mediated by a reduction of this tone. However, the neurotransmitorial modifications involved in the rhythmic secretion of the H-A-A axis are still obscure. So chrononeuroendocrine study of the H-A-A axis in various psychoneuroendocrine diseases is of great interest in clearing up the neurotransmitorial mechanisms of this rhythm. Primary depression represents an interesting model being characterized by monoaminergic neurotransmitorial alterations. We have observed in this pathology an increase of the H-A-A axis activity and an alteration of the circadian cortisol profile characterized by an increase both in numeric and quantitative secretory bursts.