Age dependence of blood fibrinolytic components and the effects of low-dose oral contraceptives on coagulation and fibrinolysis in teenagers.

Basal t-PA antigen concentration, PAI-I activity and fibrinolytic capacity was studied in plasma from 20 healthy teenager girls (age 15.9 +/- 1.3 years) and two groups of older healthy volunteers, consisting of 17 women (age 32 +/- 8 years, group 1) and 35 men (age 34 +/- 8 years, group 2). Basal t-PA antigen concentrations in plasma were found to be highly age-dependent with higher values with increasing age. The teenager girls had significantly lower values compared with the two groups of elderly volunteers. PAI-I levels were significantly higher in plasma from the teenager girls and the fibrinolytic capacity after 15 min of venous occlusion was significantly lower. In this study we also determined the effect of low-dose oral contraceptives (OC) on coagulation and fibrinolysis in the teenager group. Each teenager served as her own control with samples drawn before and on OC after 4 months of use. The coagulation parameters, factor VIII activity, AT III, Protein C and platelet counts were all within reference values before and on OC. The fibrinolytic activity in plasma after venous occlusion (15 min) increased significantly when the teenagers had used OC for 4 months. This phenomenon was explained by significantly decreased PAI levels and also by significantly increased t-PA antigen release from the vessel wall after venous occlusion.