title: Effects of 17beta-estradiol replacement on the apoptotic effects caused by ovariectomy in the rat hippocampus.
abstract: OBJECTIVE
  The aim of the present study was to investigate the effects of different periods of ovariectomy and 17beta-estradiol replacement on apoptotic cell death and expression of members of the Bcl-2 family in the rat hippocampus.
  
  
  METHODS
  Hippocampi were obtained from rats in proestrus, ovariectomized (15 days, 21 days and 36 days), ovariectomized for 15 days and then treated with 17beta-estradiol for 7 or 21 days, and rats ovariectomized and immediately treated with 17beta-estradiol for 21 days. The expression of Bcl-2 and Bax and the number of apoptotic cells were determined.
  
  
  RESULTS
  Ovariectomy decreased Bcl-2 expression and increased Bax expression and the number of apoptotic cells. Replacement with 17beta-estradiol (21 days) throughout the post-ovariectomy period reduced the number of apoptotic cells to the control levels, and prevented the effects of ovariectomy on Bax expression, but only partially restored the Bcl-2 expression. After 15 days of ovariectomy, the replacement with 17beta-estradiol for 21 days, but not for 7 days, restored the Bcl-2 and Bax expression and the percentage of apoptotic cells to the levels found in the proestrus control.
  
  
  CONCLUSIONS
  The present results show that a physiological concentration of 17beta-estradiol may help maintain long-term neuronal viability by regulating the expression of members of the Bcl-2 family. Even after a period of hormonal deprivation, treatment with 17beta-estradiol is able to restore the expression of Bax and Bcl-2 to control levels, but the duration of the treatment is a key factor to obtain the desired effect. These data provide new understanding into the mechanisms contributing to the neuroprotective action of estrogen.
authors.affiliation: Laboratory of Pharmacology, Instituto Butantan, Brazil.
authors.forename: Sayuri
authors.initials: S
authors.lastname: Sales
authors.forename: Rodrigo Portes
authors.initials: RP
authors.lastname: Ureshino
authors.forename: Renato Tavares dos Santos
authors.initials: RT
authors.lastname: Pereira
authors.forename: Milene Schmidt Amaral
authors.initials: MS
authors.lastname: Luna
authors.forename: Marcelo
authors.initials: M
authors.lastname: Pires de Oliveira
authors.forename: Norma
authors.initials: N
authors.lastname: Yamanouye
authors.forename: Rosely Oliveira
authors.initials: RO
authors.lastname: Godinho
authors.forename: Soraya Soubhi
authors.initials: SS
authors.lastname: Smaili
authors.forename: Catarina Segreti
authors.initials: CS
authors.lastname: Porto
authors.forename: Fernando Maurício Francis
authors.initials: FM
authors.lastname: Abdalla
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015153:Blotting, Western; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006624:Hippocampus / Q000737:chemistry / Q000187:drug effects* / Q000503:physiopathology; D010052:Ovariectomy / Q000009:adverse effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D051028:bcl-2-Associated X Protein / Q000032:analysis
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D004958:Estradiol