ACTH secretion regulation

A major stimulus to CRF and ACTH release is stress, which could, for example, be the result of accident or trauma, infections, anxiety or reduction in blood sugar. ACTH release is regulated by CRF and blood levels of ACTH regulate cortisol secretion via a negative feedback mechanism. As cortisol levels rise, ACTH secretion is reduced, and vice versa. 

There is a major negative feedback loop involving the hypothalamus, corticotrophin-releasing hormone, corticotropin (=ACTH) secreted by the pituitary and corticosteroids from the adrenal cortex, which dampen pro-inflammatory cytokine production. This loop normally acts to stabilise immune system activity, but it also has spillover effects on appetite and weight regulation. 

Under normal conditions the secretion of ACTH by the pituitary is related to the plasma cortisol concentration. A rise in plasma cortisol reduces the ACTH output of the pituitary. During surgical procedures the regulation of ACTH secretion is altered and levels of plasma cortisol which normally suppress ACTH output no longer do so and plasma ACTH levels rise. During surgical procedures the concentration of... 

The nonrenal actions of vasopiessin include its vasneon-.strictor effects and ncurotransmittcr actions in the cxmnl nervous system, such as regulation of ACTH secretion, circulation. and body tempcratuic. 

ACTH that regulates the growth of the adrendt glands and the synthesis and secretion of adrenal gland hormones (see Chapters 50 and 51). 

Concentrations of hypothalamic and anterior pituitary peptides and adrenal glucocorticoids are measured accurately and at low concentrations in body fluids using immunoassay and instrumental methods. Relying on basal hormone concentrations for confirmmg adrenocortical dysfunction, however, can be problematic because of the episodic and circadian secretion of the hormones that regulate the HPA axis. For example, some individuals have an abnormality of the HPA axis, but still maintain basal cortisol and ACTH secretion within die reference interval of the normal population. Dynamic testing of the HPA axis helps define abnormalities that are not reflected in basal hormone secretion. 

The syndrome is due to the combination of the enzymatic defect producing a deficient proportion of cortisol and corticosterone in the secreted products of the adrenal cortex, and the normal response to this deficiency of the system regulating the secretion of ACTH. In the absence of the negative feedback of a normal concentration of plasma cortisol, ACTH secretion is increased. Since the action of ACTH on the adrenal cortex is to stimulate a very early step in the biosynthetic pathway (Fig. 3), the production of aU products subsequent to this step is increased. 

Lumpkin, M. D. The regulation of ACTH secretion by IL-1. Science 238, 452-454 (1987). Luscinskas, F. W., Brock, A. F., Amaout, M. A., and Gimbrone, M. A., Jr. Endothelial-leukocyte adhesion molecule-1-dependent and leukocyte (CDll/CD18)-dependent mechanisms contribute to polymorphonuclear leukocyte adhesion to cytokine-activated human vascular endothelium. J. Immunol. 142, 2257-2263 (1989). 

Hormones, such as the adrenocorticotrophic hormone (ACTH), appear to regulate the concentration of zinc in the liver. ACTH, secreted by the anterior pituitary gland, stimulates the secretion of... 

In fact, ACTH secretion is regulated by a neuro-hormonal mechanism and a humoral feedback mechanism. The neurohormonal control of ACTH secretion involves what has been referred to as a third-order neuroendocrine mechanism. Three steps are involved in this control. A stimulus (stress, for example) brings the central nervous system to secrete a hormone (CRF), which acts on another endocrine structure in the anterior lobe of the hypophysis where it induces the secretion of second hormone (ACTH), which ultimately acts on the target endocrine gland—the adrenal cortex [40, 56-60]. 

THE PHABMCOLOGICAL APPROACH TO THE STUDT OF THE MECHANISMS REGULATING ACTH SECRETION... 

The common association of sympathoadrenal and pituitary adrenocortical activity in stress has suggested that catecholamines play a special role in regulating ACTH secretion. Several theories have been proposed through the years to explain this relationship. These included (a) Long s concept (l952) that emotional stimuli activate the hypothalamus which in turn stimulates the adrenal medulla via the spinal cord and splanchnic nerves, and the subsequently released epinephrine stimulates the release of ACTH ... 

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