A Method for the Estimation of Human Plasma Kininogens I and II

Abstract

A practical method for the estimation of plasma kininogens I and TI was described. The level of kininogen I was calculated as difference between total kininogen and kininogen II. One-tenth milliliter of heparinized plasma was in-cubated with 1.2 Frey units of human plasma kallikrein in 0.05M phosphate buffer, pH 7.4, at 37°C for 45 minutes to deplete kininogen I completely. It was then heated at 62°C for 15 minutes and incubated with 100μg of trypsin at 37°C for 45 minutes to release bradykinin from kininogen IT. To measure the total kininogen level (kininogens I and II), 0.1ml of plasma was first heated at 62°C for 15 minutes in 0.05 M phosphate buffer, pH 7.4. It was then incubated with 100μg of trypsin at 37°C for 45 minutes. Released plasma kinin was assayed on the isolated rat uterus against synthetic bradykinin as a standard. Total kininogen and kininogen II levels were expressed as the amount of bradykinin released by these procedures. In 10 healthy subjects, the estimated levels for plasma kininogens I and IT lc ere 2.48±10.28 and 3.15±0.55μg bradykinin equivalent per milliliter, respeetieely. It seems essential to estimate the changes of kininogens I and II instead of total kininogen for the study of plasma kallikrein-kinin system in pathological and physiological conditions.