title: [27- Hydroxycholesterol reverses estradiol induced inhibition of platelet aggregation in postmenopausal women].
abstract: BACKGROUND
  The decline of estrogen levels increases cardiovascular risk in women. Platelets express estrogen receptors and 17β-estradiol- (E2) can produce a protective effect on thrombus formation. The hydroxylation of cholesterol generates several sterols and 27-hydroxycholesterol (27HC) predominates in circulation.
  
  
  OBJECTIVE
  To evaluate the effect of 27HC as an endogenous antagonist of the anti-aggregating properties of E2 in platelets of postmenopausal women.
  
  
  METHODS
  Platelet function of postmenopausal women was evaluated ex-vivo. Platelets pre-incubated with 27HC in the presence or absence of E2, were stimulated with collagen. Aggregation was evaluated using turbidimetry using a Chrono-log aggregometer.
  
  
  RESULTS
  Collagen-stimulated platelet aggregation was significantly inhibited by E2. The inhibitory effect of E2 on collagen-stimulated platelet aggregation was significantly reversed in the presence of 27HC.
  
  
  CONCLUSIONS
  The suppressive effect of E2 on platelet aggregation is inhibited by 27HC, which could contribute to increase cardiovascular risk in postmenopausal women.
authors.affiliation: Instituto de Nutrición y Tecnología de los Alimentos Dr. Fernando Monckeberg, Universidad de Chile, Santiago, Chile, lvallada@inta.uchile.cl.
authors.forename: Gladys
authors.initials: G
authors.lastname: Rocha
authors.affiliation: Instituto de Nutrición y Tecnología de los Alimentos Dr. Fernando Monckeberg, Universidad de Chile, Santiago, Chile, lvallada@inta.uchile.cl.
authors.forename: Walter
authors.initials: W
authors.lastname: Sierralta
authors.affiliation: Instituto de Nutrición y Tecnología de los Alimentos Dr. Fernando Monckeberg, Universidad de Chile, Santiago, Chile, lvallada@inta.uchile.cl.
authors.forename: Luis
authors.initials: L
authors.lastname: Valladares
mesh_terms: D000368:Aged; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002318:Cardiovascular Diseases / Q000209:etiology; D003094:Collagen / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism; D004965:Estrogen Antagonists / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology*; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors; D017698:Postmenopause / Q000097:blood*; D012016:Reference Values; D012307:Risk Factors; D018709:Statistics, Nonparametric
chemical_list: D004965:Estrogen Antagonists; D004967:Estrogens; D006888:Hydroxycholesterols; D010975:Platelet Aggregation Inhibitors; D004958:Estradiol; C076996:27-hydroxycholesterol; D003094:Collagen