A comparison of the effects of intravenous serotonin and dextran on the levels of factor XII, prekallikrein and plasminogen in rat plasma.

It was previously observed that serotonin injected intravenously into the rat caused significant reductions in the prekallikrein activator (PKA) and the benzoyl arginine ethyl ester (BAEe)-esterase activities induced in rat plasma by acetone/kaolin activation. In the present work it was demonstrated that serotonin was unable to exert these effects in vitro, in plasma or in whole blood. The assay of PKA and Baee-esterase activities after gel filtration on Sephadex G-100 of acetone-activated plasma from rats treated with serotonin 0.10 mg/kg revealed reduced fragmentation of factor XII, and reduced levels of kallikrein and of an additional BAEe-esterase. Serotonin also lowered the plasminogen level. The serotonin-induced reductions of PKA and BAEe-esterase were inhibited by pretreatment of the rats with epsilon-aminocaproic acid. Evidence was provided that serotonin did not lower the plasma level of factor XII of the coagulation system, but the level of a factor of significance for the activation of factor XII. All the above-mentioned serotonin effects were fundamentally similar to the corresponding effects caused by dextran. It is concluded that the effects of dextran on the plasma parameters mentioned are mediated by the release of endogenous serotonin.