The Destruction of Glucagon by the Blood Plasma From Various Species¹

Glucagon is hydrolyzed in vitro by blood plasma from various species. The highest rates occur with the plasmas from monkey and rat. Much lower rates of glucagonolysis are produced by plasmas from guinea-pig, chicken, man, rabbit, cow, dog and cat. The addition of streptokinase to the incubation mixture increases markedly the glucagonolytic activity of the plasmas from man, monkey and cat. In the presence of trace amounts of human plasma or of a crude euglobulin fraction of human plasma, streptokinase increases the glucagonolytic activity of the plasmas (or euglobulin fractions of such plasmas) from the various species. The data indicate that plasmin is responsible for the glucagonotytic action of plasma and that the activation of plasminogen by streptokinase is dependent upon a ‘proactivator’ which is present in human, monkey and cat plasmas, and absent or very low in the plasmas from the other species. It is proposed that the glucagonolytic action of native plasma is due to the release of endogenous activators of plasminogen and reflects a more general action of plasmin.