Normal and abnormal function of the hypothalamic pituitary-adrenocortical system in man

Abstract

The hypothalamic-pituitary-adrenocortical (HPA) system has three well known functional attributes in normal human subjects: First, under unstressed conditions of daily life there is a circadian rhythm of activity of the system. These rhythmical fluctuations are manifested by highest plasma cortisol concentrations shortly after awakening and lowest levels when asleep. Normal health is associated not only with such circadian changes but also with appropriate total daily secretion of cortisol, so that daily integrated plasma cortisol concentration, cortisol secretion rate, and excretion of cortisol metabolites all fall within definable normal ranges, below or above which symptoms and signs of ill health often become evident. Second, the prevailing plasma cortisol (or glucocorticoid) concentration at any time of the day influences the activity of the HPA system. Such negative feedback control results in stimulation of the system when the plasma cortisol concentration falls, and inhibition of the system when plasma cortisol or glucocorticoid concentration is raised. © 1984 by The Endocrine Society.