Cold promoted activation and factor XII, prekallikrein and C1-inhibitor.

During incubation of plasma in the cold an amidolytic activity due to the kallikrein-alpha 2-macroglobulin complex appears in the plasma of about 40% of the women under hormonal contraception. The factor XII and prekallikrein activity are significantly increased 151.9% and 112.4% respectively in the cold promoted activation positive plasmas (CPA pos) whereas the activity of C1-inhibitor is decreased, 76%. The quotient of the product of the C1-inhibitor and alpha 2-macroglobulin values divided by the product of the FXII and prekallikrein values is significantly lower in the CPA pos plasma 0.49 than in CPA neg plasma 0.96 (p less than 0.05). These results alone do not explain the cold promoted activation, since a patient with a C1-inhibitor as low as 9% showed no increase of the amidolytic activity after a 24 hr incubation at 4 degrees C. However, the addition of purified C1-inhibitor to a CPA pos. plasma inhibits the cold activation. Heparin at a concentration of 0.5 IU/ml delays the appearance of the amidolytic activity.