The possible role of vasoactive substances for the hemodynamic effects of rapidly injected antilymphocyte globulin.

A rapid intravenous injection of ALG into splenectomized dogs induced an almost complete elimination of lymphocytes and an extensive but partly reversible thrombocytopenia during which platelets were trapped in the lung. During this trapping there was a significant decrease in arterial blood pressure, pulmonary blood volume and cardiac output concomitant with a marked increase in the portal pressure. The pulmonary arterial pressure remained unchanged. The hemodynamic effects are probably caused by a release of vasoactive substances which induced a decreased venous return from splanchnic pooling and statis. Prostaglandins and histamine seem to play a dominant role, since Aspirin, promethazine and 48/80 markedly reduced the side-effects.