Kininogen changes in human plasma following a test meal or insulin administration

The effect of food intake and of insulin on plasma bradykinin (BK) reserves [total (TK), high-molecular-weight (HK), and low-molecular-weight kininogen (LK)] was followed by determining (by enzyme-linked immunosorbent assay) the amount of BK released by trypsin from plasma collected before and after a test meal or hyperinsulinemic clamping. LK was kininogen remaining in plasma after in vitro kaolin treatment, which removes all HK. HK was the difference between TK and LK. Thirty minutes after a test meal, TK and HK decreased by 8.0 +/- 0.6 and 39.7 +/- 6.6%, respectively, in six of seven subjects. Return to prealimentary levels occurred after 90-120 min. Hyperinsulinemia, comparable to that arising after the test meal, partly reproduced such treatment's effect on TK and HK but did not affect blood or plasma kininogen in vitro. Observed postprandial hypotension and increased leg blood flow could be caused, in part, by BK released from plasma HK after cleavage at vascular, possibly endothelial, sites activated by insulin.