Vascular biology in the menstrual cycle, pregnancy and pre-eclampsia

BACKGROUND Thrombotic disease is rare but significant in women of reproductive age. Thrombosis and thromboembolism are the most common causes of maternal death in the United Kingdom. Pre-eclampsia is associated with increase in immediate and lifetime risk of adverse thrombotic events. Both pregnancy and the follicular phase are associated with arterial thrombosis and myocardial infarction. Modulation of haemostatic mechanisms in reproductive physiology and disease is not well understood. Outwith pregnancy, stimulated tissue plasminogen activator (t-PA) release, platelet activation, arterial stiffness and circulating endothelial progenitor cell (EPC) number are established indicators of vascular pathology and prognosis. AIMS (i) To compare endogenous fibrinolysis between pregnant women and non-pregnant control women, (ii) To make serial measurements of reproductive hormones, inflammatory mediators, platelet and monocyte activation, arterial stiffness and circulating EPCs throughout the normal menstrual cycle, healthy pregnancy, and pregnancy affected by pre¬ eclampsia. METHODS (i) Endogenous fibrinolytic capacity was assessed using forearm venous sampling and plethysmography during intra-arterial infusion of bradykinin (a known stimulant of endothelial t-PA release). Healthy women in the third trimester were recruited from antenatal clinics. Healthy volunteers were studied in their follicular phase, (ii) Platelet-monocyte aggregates and surface markers of platelet and monocyte activation were assessed with flow cytometry. Reproductive hormones, inflammatory mediators (soluble intercellular adhesion molelcule-l (ICAM-1), interleukin-6 (IL-6), tumour necrosis factor alpha (TNF-a)) and soluble markers of platelet activation were measured by enzyme-linked immunosorbent assay (ELISA). Arterial stiffness was derived using pulse wave analysis (PWA) and pulse wave velocity (PWV). Circulating EPCs were assessed by flow cytometry and cell culture. All measurements were taken longitudinally in three different populations: healthy women during a single menstrual cycle (4 time points), healthy pregnant women (4 time points and post-partum) and women with pre-eclampsia (at diagnosis and post-partum). RESULTS (i) Pregnant women had more plasminogen activator inhibitor type 1 (PAI-1) antigen and lower active t-PA plasma concentrations than non-pregnant women, (ii) Pregnant women had greater platelet and monocyte activation, plasma soluble ICAM-1 and IL-6 than non-pregnant women. There was no difference in platelet activation or inflammatory mediators between healthy and pre-eclamptic pregnant women. Systemic arterial stiffness varies during the menstrual cycle. In pregnancy both systemic and central arterial stiffness are lowest during the second trimester. Arterial stiffness was greater in pre¬ eclampsia and this persisted post-partum, despite blood pressure returning to normal. Concentration of EPCs (cytometry) varied during the menstrual cycle and was greatest in the follicular phase. Endothelial progenitor cell colony formation was reduced in healthy pregnancy compared to the follicular phase. There was no difference in either EPC assay between healthy and pre-eclamptic pregnant women. CONCLUSIONS Important constituents of thrombotic and inflammatory activity are observed to vary with normal changes in reproductive status. No difference was observed in these factors between healthy pregnant and pre-eclamptic women. Greater arterial stiffness was observed in pre-eclamptic women, also continuing after pregnancy. This may contribute to the increased immediate and lifetime risk of vascular disease in these women. Variation in circulating EPCs during the menstrual cycle may be due to a role in endometrial angiogenesis.