Adrenal steroid endocrinology--some unsolved problems.

Although we now have a good understanding of some of the mechanisms which control pituitary-adrenal activity in human subjects, there are several important problems which still require a solution. The mechanism which controls the diurnal rhythm of aldosterone secretion is not yet identified, and although ACTH is clearly an important factor in the control of adrenocortical activity, it does not account for the pattern of these changes, or for the changes which occur in adrenal androgen secretion. Corticosteroids are well known to have suppressive effects on the release of ACTH, but the retention of pituitary-adrenal responsiveness in patients receiving ACTH therapy, and the prolonged suppression of the system caused by cortisol-secreting tumours, are not well explained by the model currently used, which needs further refinement.