Chapter 4.2 Sympatho-adrenal activity and hypothalamic-pituitary-adrenal axis regulation

The secretion of glucocorticoids from the adrenal cortex is considered an essential adaptive component of the response to stress. Although adrenocorticotropic hormone (ACTH) regulates adrenal steroidogenesis, the dissociation between changes in plasma ACTH and glucocorticoids under nonstress and stress conditions has prompted the search for alternative non-ACTH mechanisms. The innervation of the adrenal cortex and the intermingling of adrenal cortical and medullary cells form the anatomical substrate for regulation of adrenocortical secretion by neural elements. In vitro studies demonstrate the effectiveness of a variety of neurotransmitters to affect adrenal steroidogenesis. In vivo experiments show that adrenal denervation alters glucocorticoid secretion under nonstress and stress conditions. Further investigations are required to reveal the full extent of neural control of adrenal steroidogenesis and to delineate the mechanisms that underlie it. Nonetheless, the collective results suggest that the brain can control glucocorticoid production by at least two complimentary mechanisms, by stimulation of the neuroendocrine hypothalamic-pituitary-adrenal axis and through direct activation of adrenal neural elements.