5-Hydroxytryptamine (serotonin) in acute hypotensive shock

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Abstract
Alterations in the circulating 5-hydroxytryptamine (5-HT), platelet counts, and the degree of blood cell aggregation were studied before and during acute hypotensive "shock," induced either by bleeding or by histamine injections in anesthetized and heparinized dogs. Although marked aggregation of blood cells was observed during shock only slight increases in 5-HT and platelet counts were found. Since earlier studies in vitro had indicated a direct relationship between aggregation of blood cells and 5-HT the reliability of the fluorometric determination of 5-HT was questioned. Subsequent experiments with C14-labeled 5-HT showed increases up to 600% in circulating radioactivity during hypotension, representing 5-HT, or its metabolites. Radioactivity increased earlier and was greatest in portal blood. Glass-wool filtration experiments showed that adhesive platelets were important in the mechanism of blood cell aggregation. UML-491, a 5-HT and blood aggregation inhibitor in vitro, was shown to prevent or lower the tendency of blood cells to aggregate in vivo during hemorrhage. These experiments indicate the importance of 5-HT in the development of blood cell aggregation during shock, and its prevention by a 5-HT antagonist.