Neuroendocrine response to injury

Neuroendocrine response to injury

Patients also respond rapidly to injury by the classical neuroen docrine pathways of the stress response, consisting of a ff erent nociceptive neurones, the spinal cord, thalamus, hypothalamus and pituitary ( Figure 1.2 ). Nociceptive neurones are ex by the e ff ects of local inflammation as well as by direct injury . The neurones terminate in the hypothalamus and release corti cotropin-releasing factor (CRF). CRF stimulates adrenocorti cotropic hor mone (ACTH) release from the anterior pituitary , which then acts on the adrenals to increase the secretion of cortisol within hours of injury . Hypothalamic activation of the sympathetic nervous system causes release of adrenaline (epinephrine) and also stimulates release of glucagon. An intravenous infusion of a cocktail of these ‘counter-regulatory’ hormones (glucagon, glucocorticoids and catecholamines) reproduces many aspects of the metabolic response to injury . The metabolic e ff ects of the acute rise in the levels of these hormones is to liberate glucose from carbohydrate stores and to begin the breakdown of fat and protein as metabolic substrates for energy and repair. There are, however, many other e ff ects, including alterations in insulin release and sensitivity , hypersecretion of prolactin and growth hormone (GH) in the presence of low circulatory insulin-like growth factor-1 (IGF-1) and inactivation of peripheral thyroid hormones and gonadal function. Of note, GH has direct lipolytic, insulin-antagonising and proinflammatory properties. Neuroendocrine response to injury/critical illness - /uni25CF /uni25CF - As described above, the innate immune system (principally macrophages), once activated by DAMPs, interacts in a complex manner with the adaptive immune system (T cells, B cells) in co-generating the metabolic response to injury ( Figure 1.2 ) . Proinflammatory cytokines including IL-1, TNF alpha (TNF α ), IL-6 and IL-8 are produced within the first 24 hours and act directly on the hypothalamus to cause pyrexia. Such cytokines also augment the hypothalamic stress response and act directly on skeletal muscle to induce pr oteolysis while inducing acute-phase protein production in the liver. Proinflammatory cytokines also play a complex role in the development of peripheral insulin resistance. Other import - ant proinflammatory mediators include nitric oxide ([NO] via inducible nitric oxide synthetase [iNOS]) and a variety of prostanoids (via cyclooxygenase-2 [Cox-2]). Changes in organ function (e.g. renal hypoperfusion/impairment) may be induced b y excessive vasoconstriction via endogenous factors such as endothelin-1. Complement and kinin pathways are also activated and processes of programmed cell death and - phagocytosis are triggered to clear damaged tissues. There are many complex interactions among the neuroendocrine, cytokine and metabolic axes. For example, cited although cortisol is immunosuppressive at high levels, it acts synergistically with IL-6 to promote the hepatic acute-phase - r esponse. ACTH release is enhanced by proinflammatory - cytokines and the noradrenergic system. The resulting rise in cortisol levels may form a weak feedback loop, attempting to limit the proinflammatory stress response. Finally , hyperglycaemia may aggravate the inflammatory response in the mitochondria, causing the formation of excess oxygen free radicals and also altering gene expression to enhance cytokine production. At the molecular level, the changes that accompany systemic inflammation are extremely complex. In one study using network-based analysis of changes in mRNA expression in leukocytes following exposure to endotoxin, ther e were changes in the expression of more than 3700 genes, with over half showing decreased expression and the remainder increased expression. The cell surface receptors, signalling mechanisms and transcription factors that initiate these events are also complex. Although the detailed mechanisms are being steadily identified, specific molecular therapies remain elusive and certainly subservient to optimal clinical care.

The neuroendocrine response to severe injury/critical illness is biphasic: Acute phase (hours) characterised by elevated counter- regulatory hormones (cortisol, glucagon, adrenaline). Changes are thought to be bene /f_i cial for short-term survival Chronic phase (days) associated with hypothalamic suppression and low serum levels of the respective target organ hormones. Changes may contribute to chronic wasting

Figure 1.2

CRF Pituitary Spinal cord Ad re nal Sympathetic nervous system Pancreas Injury Afferent Adaptive noiciceptive immune pathways system The integrated response to surgical injury ( /f_i rst 24–48 hours): there is a complex interplay between the neuroendocrine stress response and the proin /f_l ammatory cytokine response of the innate immune system. ACTH, adrenocorticotropic hormone; GH, growth hormone; IGF , insulin-like growth factor; IL, interleukin; T3, triiodothyronine; TNF

Neuroendocrine response to injury

Patients also respond rapidly to injury by the classical neuroen docrine pathways of the stress response, consisting of a ff erent nociceptive neurones, the spinal cord, thalamus, hypothalamus and pituitary ( Figure 1.2 ). Nociceptive neurones are ex by the e ff ects of local inflammation as well as by direct injury . The neurones terminate in the hypothalamus and release corti cotropin-releasing factor (CRF). CRF stimulates adrenocorti cotropic hor mone (ACTH) release from the anterior pituitary , which then acts on the adrenals to increase the secretion of cortisol within hours of injury . Hypothalamic activation of the sympathetic nervous system causes release of adrenaline (epinephrine) and also stimulates release of glucagon. An intravenous infusion of a cocktail of these ‘counter-regulatory’ hormones (glucagon, glucocorticoids and catecholamines) reproduces many aspects of the metabolic response to injury . The metabolic e ff ects of the acute rise in the levels of these hormones is to liberate glucose from carbohydrate stores and to begin the breakdown of fat and protein as metabolic substrates for energy and repair. There are, however, many other e ff ects, including alterations in insulin release and sensitivity , hypersecretion of prolactin and growth hormone (GH) in the presence of low circulatory insulin-like growth factor-1 (IGF-1) and inactivation of peripheral thyroid hormones and gonadal function. Of note, GH has direct lipolytic, insulin-antagonising and proinflammatory properties. Neuroendocrine response to injury/critical illness - /uni25CF /uni25CF - As described above, the innate immune system (principally macrophages), once activated by DAMPs, interacts in a complex manner with the adaptive immune system (T cells, B cells) in co-generating the metabolic response to injury ( Figure 1.2 ) . Proinflammatory cytokines including IL-1, TNF alpha (TNF α ), IL-6 and IL-8 are produced within the first 24 hours and act directly on the hypothalamus to cause pyrexia. Such cytokines also augment the hypothalamic stress response and act directly on skeletal muscle to induce pr oteolysis while inducing acute-phase protein production in the liver. Proinflammatory cytokines also play a complex role in the development of peripheral insulin resistance. Other import - ant proinflammatory mediators include nitric oxide ([NO] via inducible nitric oxide synthetase [iNOS]) and a variety of prostanoids (via cyclooxygenase-2 [Cox-2]). Changes in organ function (e.g. renal hypoperfusion/impairment) may be induced b y excessive vasoconstriction via endogenous factors such as endothelin-1. Complement and kinin pathways are also activated and processes of programmed cell death and - phagocytosis are triggered to clear damaged tissues. There are many complex interactions among the neuroendocrine, cytokine and metabolic axes. For example, cited although cortisol is immunosuppressive at high levels, it acts synergistically with IL-6 to promote the hepatic acute-phase - r esponse. ACTH release is enhanced by proinflammatory - cytokines and the noradrenergic system. The resulting rise in cortisol levels may form a weak feedback loop, attempting to limit the proinflammatory stress response. Finally , hyperglycaemia may aggravate the inflammatory response in the mitochondria, causing the formation of excess oxygen free radicals and also altering gene expression to enhance cytokine production. At the molecular level, the changes that accompany systemic inflammation are extremely complex. In one study using network-based analysis of changes in mRNA expression in leukocytes following exposure to endotoxin, ther e were changes in the expression of more than 3700 genes, with over half showing decreased expression and the remainder increased expression. The cell surface receptors, signalling mechanisms and transcription factors that initiate these events are also complex. Although the detailed mechanisms are being steadily identified, specific molecular therapies remain elusive and certainly subservient to optimal clinical care.

The neuroendocrine response to severe injury/critical illness is biphasic: Acute phase (hours) characterised by elevated counter- regulatory hormones (cortisol, glucagon, adrenaline). Changes are thought to be bene /f_i cial for short-term survival Chronic phase (days) associated with hypothalamic suppression and low serum levels of the respective target organ hormones. Changes may contribute to chronic wasting

Figure 1.2

CRF Pituitary Spinal cord Ad re nal Sympathetic nervous system Pancreas Injury Afferent Adaptive noiciceptive immune pathways system The integrated response to surgical injury ( /f_i rst 24–48 hours): there is a complex interplay between the neuroendocrine stress response and the proin /f_l ammatory cytokine response of the innate immune system. ACTH, adrenocorticotropic hormone; GH, growth hormone; IGF , insulin-like growth factor; IL, interleukin; T3, triiodothyronine; TNF

Neuroendocrine response to injury

Patients also respond rapidly to injury by the classical neuroen docrine pathways of the stress response, consisting of a ff erent nociceptive neurones, the spinal cord, thalamus, hypothalamus and pituitary ( Figure 1.2 ). Nociceptive neurones are ex by the e ff ects of local inflammation as well as by direct injury . The neurones terminate in the hypothalamus and release corti cotropin-releasing factor (CRF). CRF stimulates adrenocorti cotropic hor mone (ACTH) release from the anterior pituitary , which then acts on the adrenals to increase the secretion of cortisol within hours of injury . Hypothalamic activation of the sympathetic nervous system causes release of adrenaline (epinephrine) and also stimulates release of glucagon. An intravenous infusion of a cocktail of these ‘counter-regulatory’ hormones (glucagon, glucocorticoids and catecholamines) reproduces many aspects of the metabolic response to injury . The metabolic e ff ects of the acute rise in the levels of these hormones is to liberate glucose from carbohydrate stores and to begin the breakdown of fat and protein as metabolic substrates for energy and repair. There are, however, many other e ff ects, including alterations in insulin release and sensitivity , hypersecretion of prolactin and growth hormone (GH) in the presence of low circulatory insulin-like growth factor-1 (IGF-1) and inactivation of peripheral thyroid hormones and gonadal function. Of note, GH has direct lipolytic, insulin-antagonising and proinflammatory properties. Neuroendocrine response to injury/critical illness - /uni25CF /uni25CF - As described above, the innate immune system (principally macrophages), once activated by DAMPs, interacts in a complex manner with the adaptive immune system (T cells, B cells) in co-generating the metabolic response to injury ( Figure 1.2 ) . Proinflammatory cytokines including IL-1, TNF alpha (TNF α ), IL-6 and IL-8 are produced within the first 24 hours and act directly on the hypothalamus to cause pyrexia. Such cytokines also augment the hypothalamic stress response and act directly on skeletal muscle to induce pr oteolysis while inducing acute-phase protein production in the liver. Proinflammatory cytokines also play a complex role in the development of peripheral insulin resistance. Other import - ant proinflammatory mediators include nitric oxide ([NO] via inducible nitric oxide synthetase [iNOS]) and a variety of prostanoids (via cyclooxygenase-2 [Cox-2]). Changes in organ function (e.g. renal hypoperfusion/impairment) may be induced b y excessive vasoconstriction via endogenous factors such as endothelin-1. Complement and kinin pathways are also activated and processes of programmed cell death and - phagocytosis are triggered to clear damaged tissues. There are many complex interactions among the neuroendocrine, cytokine and metabolic axes. For example, cited although cortisol is immunosuppressive at high levels, it acts synergistically with IL-6 to promote the hepatic acute-phase - r esponse. ACTH release is enhanced by proinflammatory - cytokines and the noradrenergic system. The resulting rise in cortisol levels may form a weak feedback loop, attempting to limit the proinflammatory stress response. Finally , hyperglycaemia may aggravate the inflammatory response in the mitochondria, causing the formation of excess oxygen free radicals and also altering gene expression to enhance cytokine production. At the molecular level, the changes that accompany systemic inflammation are extremely complex. In one study using network-based analysis of changes in mRNA expression in leukocytes following exposure to endotoxin, ther e were changes in the expression of more than 3700 genes, with over half showing decreased expression and the remainder increased expression. The cell surface receptors, signalling mechanisms and transcription factors that initiate these events are also complex. Although the detailed mechanisms are being steadily identified, specific molecular therapies remain elusive and certainly subservient to optimal clinical care.

The neuroendocrine response to severe injury/critical illness is biphasic: Acute phase (hours) characterised by elevated counter- regulatory hormones (cortisol, glucagon, adrenaline). Changes are thought to be bene /f_i cial for short-term survival Chronic phase (days) associated with hypothalamic suppression and low serum levels of the respective target organ hormones. Changes may contribute to chronic wasting

Figure 1.2

CRF Pituitary Spinal cord Ad re nal Sympathetic nervous system Pancreas Injury Afferent Adaptive noiciceptive immune pathways system The integrated response to surgical injury ( /f_i rst 24–48 hours): there is a complex interplay between the neuroendocrine stress response and the proin /f_l ammatory cytokine response of the innate immune system. ACTH, adrenocorticotropic hormone; GH, growth hormone; IGF , insulin-like growth factor; IL, interleukin; T3, triiodothyronine; TNF