The effect of the menstrual cycle and of ethinylestradiol on nitric oxide, endothelin-1 and homocysteine plasma levels.

The use of the estrogen ethinylestradiol is associated with an increased cardiovascular risk. It is not known whether this might be caused by an influence of ethinylestradiol on endothelium-derived factors or on the cardiovascular risk factor homocysteine. Our aim was to evaluate whether a short-term treatment with ethinylestradiol results in changes of nitric oxide (NO), endothelin-1 and homocysteine. Participants were ten healthy women with regular menstrual cycles. NO, homocysteine, endothelin-1, estradiol and progesterone were measured during one cycle and before and after treatment with ethinylestradiol at 50 microg/day. Homocysteine and NO did not change significantly during the menstrual cycle or after treatment. However, endothelin-1 levels decreased during the cycle (from 3.89 ng/l to 2.93 ng/l p < 0.05) and after ethinylestradiol (from 2.94 ng/l to 2.26 ng/l p<0.03). Analysis of the pretreatment data showed a positive correlation between homocysteine and NO and between NO and endothelin-1. Treatment with ethinylestradiol caused a shift in the balance between NO and endothelin-1 in the direction of vasodilatation. This finding is one factor concerning the effects of ethinylestradiol on the vascular system but does not explain the cardiovascular risk of this substance.