Neuroendocrine defence in endotoxin shock (a review).

Mild infection or sublethal dose of endotoxin elicits a brief elevation of GH and PRL in the serum. These hormones have proinflammatory and immunostimulatory effect. In severe trauma, sepsis and shock, GH and PRL are suppressed, whereas glucocorticoids and catecholamines are elevated. Under these conditions an acute phase response is initiated by tissue derived (cytokine) hormones, namely IL-1, IL-6, TNF alpha, and several others, which elicit a neuroendocrine response and initiate major metabolic alterations. There is fever and catabolism prevails, whereas the synthesis of acute phase proteins in the liver, cell proliferation in the bone marrow, and protein synthesis by leukocytes is elevated. This is an emergency reaction to save the organism after the local immune/inflammatory response has failed to contain and eliminate the infectious agent. During sepsis and endotoxin shock the systemic activation of the complement system and of leukocytes releasing enzymes and highly toxic cytokines seriously threaten survival. Glucocorticoids suppress proinflammatory cytokine production and potentiate the secretion of acute phase proteins. Some of these proteins, such as C reactive protein, or LPS binding protein, are designed to combine with microorganisms and trigger their destruction by the activation of complement system and of phagocytes. The increased production of some complement components also helps host resistance. The rise in serum fibrinogen promotes blood clotting which can serve to isolate the invading agent by triggering thrombosis in infected tissues. A number of enzyme inhibitors are produced as acute phase proteins, which are likely to serve to curb the nonspecific damage inflicted by enzymes released from activated phagocytes and from damaged cells into the circulation during sepsis and shock. Catecholamines are also elevated, which serve to inhibit inflammatory responses and to promote, even initiate, the acute phase response. If the acute phase reaction fails to protect the host, shock will develop. Patients with subclinical adrenal insufficiency succumb to septic shock almost invariably if glucocorticoid therapy is not given. However, glucocorticoid treatment of septic patients with normal adrenal function has not been helpful. The use of antibiotics to control infection did not lead to spectacular success either because of the emergence of resistant bacterial strains or the enhanced release of endotoxin by this therapy. The new approaches to prevent and treat septic shock involve the use of antibodies capable of neutralizing LPS and of cytokines and the inhibition of cytokine action by antagonist agents.