Role of the sympathetic nervous system in hemorrhage.

Abstract

The activation of the sympathetic nervous system after severe hemorrhage exerts initially beneficial effects by stimulating the cardiac contractility, reducing the venous capacity, increasing the peripheral resistance in selective areas, and favoring transcapillary fluid influx. The removal of the sympathetic system reduces the tolerance to acute and severe hemorrhage. During trie early phase after hemorrhage, when the endogenous sympathetic activity is not fully developed, norepi-nephrine administration may be beneficial. With prolonged hemorrhagic hypotension, the continued sympathetic vasoconstriction in the abdominal viscera results in a progressive aggravation of anaerobic metabolism and acidosis. Eventually the cardiovascular and other body systems may be adversely affected. There is some evidence that at mis time noreplnephrine is detrimental and sympathetic blocking agents are beneficial. During prolonged hemorrhagic hypotension, there is a reduction of the reactivity of the precapillary resistance vessels to sympathetic influence and, in some animals, a gradual decrease of sympathetic efferent impulses.