The meal-related peak in plasma cortisol is not mediated by radioimmunoassayable ACTH

There is evidence for the existence of ACTH-unrelated mechanisms in the regulation of cortisol secretion in man. The present study was designed to elucidate the interrelations between plasma ACTH and cortisol levels during the 'midday surge' in cortisol concentrations. For comparison, a 'midday surge' was imitated by infusing small amounts of ACTH in dexamethasone-suppressed subjects. The meal-related cortisol bursts were not preceded by an adequate increase in ACTH levels. In contrast, markedly elevated ACTH levels were necessary to produce a comparable cortisol peak by administration of ACTH. Apparently, the meal-related bursts in cortisol levels were not mediated by radioimmunoassayable ACTH. These findings argue against the classic concept that the adrenal cortex is inseparably linked to immediately preceding hormonal events occurring in the hypothalamo-pituitary system.