title: Circulating microparticles and endogenous estrogen in newly menopausal women.
abstract: BACKGROUND
  Estrogen modulates antithrombotic characteristics of the vascular endothelium and the interaction of blood elements with the vascular surface. A marker of these modulatory activities is formation of cell-specific microparticles. This study examined the relationship between blood-borne microparticles and endogenous estrogen at menopause.
  
  
  METHODS
  Platelet activation and plasma microparticles were characterized from women being screened (n = 146) for the Kronos Early Estrogen Prevention Study. Women were grouped according to serum estrogen (< 20 pg/ml; low estrogen, n = 21 or > 40 pg/ml; high estrogen, n = 11).
  
  
  RESULTS
  Age, body mass index, blood pressure and blood chemistries were the same in both groups. No woman was hypertensive, diabetic or a current smoker. Platelet counts, basal and activated expression of P-selectin on platelet membranes were the same, but activated expression of glycoprotein IIb/IIIa was greater in the high-estrogen group. Numbers of endothelium-, platelet-, monocyte- and granulocyte-derived microparticles were greater in the low-estrogen group. Of the total numbers of microparticles, those positive for phosphatidylserine and tissue factor were also greater in the low-estrogen group.
  
  
  CONCLUSIONS
  These results suggest that, with declines in endogenous estrogen at menopause, numbers of procoagulant microparticles increase and thus may provide a means to explore mechanisms for cardiovascular risk development in newly menopausal women.
authors.affiliation: Department of Surgery, College of Medicine, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: M
authors.initials: M
authors.lastname: Jayachandran
authors.forename: R D
authors.initials: RD
authors.lastname: Litwiller
authors.forename: W G
authors.initials: WG
authors.lastname: Owen
authors.forename: V M
authors.initials: VM
authors.lastname: Miller
mesh_terms: D001792:Blood Platelets / Q000737:chemistry / Q000648:ultrastructure; D002318:Cardiovascular Diseases; D055252:Cell-Derived Microparticles / Q000737:chemistry; D003430:Cross-Sectional Studies; D042783:Endothelial Cells / Q000648:ultrastructure; D004967:Estrogens / Q000097:blood*; D005260:Female; D006098:Granulocytes / Q000648:ultrastructure; D006801:Humans; D008593:Menopause / Q000097:blood*; D008875:Middle Aged; D009000:Monocytes / Q000648:ultrastructure; D010718:Phosphatidylserines / Q000097:blood; D010976:Platelet Count; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000032:analysis; D012307:Risk Factors
chemical_list: D004967:Estrogens; D010718:Phosphatidylserines; D019039:Platelet Glycoprotein GPIIb-IIIa Complex