3 - Hypothalamic–pituitary–adrenocortical axis

Abstract

This chapter focuses on hypothalamic–pituitary–adrenocortical axis disorders. Adrenocortical hypofunction may be either primary or secondary to a failure of ACTH production caused either by hypothalamic–pituitary disease or from suppression following treatment with pharmacological doses of steroids. The clinical features of primary adrenal hypofunction are tiredness, anorexia and nausea, pigmentation, vomiting, weight loss, and hypotension. In secondary adrenocortical hypofunction caused by hypothalamic–pituitary disease, these may also be associated with the features of hypopituitarism. In primary adrenal insufficiency, there is often an increase in plasma potassium and urea with a fall in sodium because of decreased aldosterone production. Adrenal cortical function is largely under the control of the (anterior) pituitary adrenocorticotrophic hormone (ACTH). Secretion of ACTH is normally subjected to three variables: nyctohemeral rhythm, a feedback mechanism, and response to stress. It is on an understanding of this overall physiological control system that the interpretation of tests of hypothalamic–pituitary–adrenal function depends. The estimation of plasma cortisol is of most value when used in conjunction with procedures that directly or indirectly stimulate or suppress the adrenal cortex.