A Bradykinin‐Like Substance in Heat‐Treated Human Plasma Protein Solution

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Abstract
The vasodepressive activity contained in a 5 per cent heat‐treated human plasma protein solution has been studied and found to be a bradykinin‐like substance. When the solution was injected intravenously into a dog at a dose of 125 to 214 mg protein per kg body weight, at a rate of 18 to 30 ml per minute, a decrease in arterial pressure of 11.5 to 25.0 per cent was observed.The solution also showed a marked contractile effect on smooth muscle of the isolated rat uterus. The extent of contraction was nearly equal to that caused by a bradykinin solution at a concentration of 25 to 125 ng/ml. The molecular weight of the vasodepressive substance is in the range of 1,000 to 10,000 as demonstrated by ultrafiltration. The substance was thermostable, dialyzable, and inactivated by carboxypeptidase B. Separation of the vasodepressive substance from the heat‐treated plasma protein was achieved either by gel filtration on Sephadex G‐50 or by selective adsorption. The active substance is probably bradykinin‐like, of molecular weight of 1,000 to 10,000, and contains lysine or arginine at its carboxyl terminal.