Inhibition of tissue-type plasminogen activator in plasma of women using oral contraceptives and in normal women during a menstrual cycle

Tissue-type plasminogen activator (t-PA) inhibition in plasma was assessed in 15 normal women and in 10 women using oral contraceptives (OC) containing 30 micrograms ethinyl oestradiol and 150 micrograms levo-norgestrel. The levels of t-PA inhibition were significantly lower in the OC group with marked fluctuations related to the hormone cycle. Normal women had only minor fluctuations. PIP: 2 groups of healthy, informed volunteers were studied to assess tissue-type plasminogen activator (t-PA) inhibition in plasma of women using oral contraception (OC) and in normal women. The women in the 1st group (n=10, age range 21-30 years) had used a combined OC with 30 mcg ethinyl estradiol and 150 mcg levonorgestrel daily for 21 days per cycle for 4 months. They began using pills on the 7th day of their cycle. The 2nd group was made up of 15 women, age 20-28 years, with a regular menstrual cycle (range of 28-31 days) and with hormone levels within the normal range. None of the women had evidence of liver disease or active thrombotic disease, and none was taking other drugs. Blood samples were obtained in the morning with a minimum of stasis from an antecubital vein from fasting subjects in the supine position after a brief rest. The t-PA inhibition in plasma was determined by amidolytic titration with purified melanoma 2-chain t-PA. The measured inhibition was arbitrarily expressed in percentages relative to a pool of normal plasma. The t-PA activity was determined on fibrin plates as the activity measured in the presence of excess of C1-inactivator as described elsewhere. The mean levels of inhibition during the cycle were lower in the OC than in the normal group. The difference were statistically significant. When the separate sampling periods were compared, a statistically significant difference between the 2 groups were obtained for periods 2-5. There were only minor and insignificant fluctuations during the normal menstrual cycle. In the OC group the inhibition decreased from periods 1-5 with a statistical significance. Within both groups the fluctuations in t-PA inhibition were almost inversely related to the t-PA activities.