Turnover of human and monkey plasma kininogens in rhesus monkeys

The normal metabolic turnover of plasma kininogens was studied by measuring the disappearance of intravenously administered radiolabeled human and monkey plasma kininogens from the circulation of healthy adult rhesus monkeys. Curves obtained by plotting log radioactivity against time could be expressed as double exponential equations, with the first term representing diffusion, and the second, catabolism. No significant difference between the turnovers of human and monkey kininogens was observed. The difference between the t1/2 of high molecular weight kininogen (25.95 +/- 1.60 h) (mean +/- SEM) and that of low molecular weight kininogen (18.94 +/- 1.93 h) was only marginally significant (P less than 0.05). In contrast, a highly significant (P less than 0.001) difference in their mean catabolic rates (1.12 +/- 0.08 d-1 for high molecular weight kininogen vs. 2.07 +/- 0.09 d-1 for low molecular weight kininogen) was observed. These differences between the two kininogens were attributed to differences in their distribution between the intra- and extravascular pools. Studies of kininogen turnover will be useful in elucidating the in vivo functions of the various kininogens in health as well as during clinical illness.