Individual levels of plasma alpha 2-antiplasmin and alpha 2-macroglobulin during the normal menstrual cycle and in women on oral contraceptives low in oestrogen.

Determinations of alpha 2-antiplasmin and alpha 2-macroglobulin were made in plasma samples collected during one normal or hormone induced cycle in 15 normal women and 11 women using oral contraceptives containing 30 micrograms ethinyl oestradiol and 150 micrograms levo-norgestrel. The immediate plasmin inhibition test for determination of alpha 2-antiplasmin was modified for application on a centrifugal analyser using the chromogenic peptide substrate Chromozym PL. alpha 2-Macroglobulin concentration was determined by radial-immunodiffusion. There were no differences between the two groups in the mean concentrations of alpha 2-antiplasmin and alpha 2-macroglobulin, but during the cycle a slight, and statistically significant fall occurred in the alpha 2-antiplasmin concentration in both groups, while the fluctuations of alpha 2-macroglobulin were small and insignificant. Distinctly individual levels of both inhibitors were found to exist. The variations in these during the periods of the cycle fluctuated within a much narrower range than the variation of the total average. The results stress the importance of determining the fluctuations in individual levels in longitudinal studies. These findings exclude variations in the concentrations of these inhibitors as possible sources of a change in the antithrombotic potential caused by oral contraceptives.