Components of the Kallikrein‐Kinin System and the Spontaneous Cold Activation of Factor VII in Human Plasma

Samples of plasma with the property of spontaneous activation of factor VII on incubation overnight at 0° were studied with regard to the concentration of prekallikrein, kininogen fractions, and the activity and concentration of proteinase inhibitors. A significantly higher concentration of prekallikrein was observed in the cold activation positive plasmas from pregnant and control subjects. The concentration of kininogen substrate 2, which was increased during pregnancy and treatment with oestrogenic oral contraceptives, was not correlated with the spontaneous cold activation. The rate of inhibition of kinino‐genase activity in normal plasma was very low at 0° as compared with that at 25°, and it is concluded that this may explain the odd temperature dependence of the spontaneous activation of factor VII.