The hypothalamo-pituitary-adrenocortical system.

Control of the secretion of ACTH appears to involve several mechanisms. It is dependent upon the release, from neurones in the hypothalamus, of corticotrophin releasing factor, which is probably a complex including CRF-41 and vasopressin. The secretion of the complex is influenced by various central inhibitory and excitatory nervous pathways. The releasing factor is conveyed by the hypophyseal portal vessels to the adenohypophysis where it stimulates the secretion of ACTH. The corticosteroids exert a profound control over the basal secretion of ACTH, but only modulate the pituitary adrenocorticotrophic response to stress. The mechanisms which may be involved are summarized in figure 8.