title: Evaluation of different periods of estrogen replacement onset in the tibia of ovariectomized rats.
abstract: OBJECTIVE
  Estrogen deficiency results in increased bone turnover and can lead to osteoporosis. Hormone replacement therapy (HRT) seems to be the most effective means of reducing bone loss and fractures. However, the effects of the period of HRT onset on bone tissue require further elucidation. This study aimed to evaluate the effects of different periods of HRT onset on the trabecular bone of ovariectomized rats.
  
  
  METHODS
  Seventy-five ovariectomized Wistar rats were divided into five groups according to the onset of treatment. Each group was subdivided into experimental (E; n = 10) and control (C; n = 5), according to treatment with 17-β-estradiol or vehicle alone (soybean oil), respectively, administered subcutaneously. The first group received treatment immediately post-surgery, while treatment in the remaining groups was initiated 1, 2, 3 and 4 weeks post-surgery. Euthanasia occurred at 9 weeks post-surgery. The left tibias were removed and prepared for histomorphometric analyses. The histomorphometric results were statistically analyzed by the Student's t test (p < 0.05).
  
  
  RESULTS
  The percentage of trabecular bone was significantly greater in the first (p = 0.002) and second (p = 0.039) experimental subgroups compared with the control for the same period. In the experimental subgroups, the percentage of trabecular bone decreased according to the delay in HRT onset and was statistically significant (t = 3.367; p = 0.0023).
  
  
  CONCLUSIONS
  These findings indicate an increase in trabecular bone loss in tibia at 9 weeks post-ovariectomy. The period of HRT/E onset is important for preventing bone loss; however, despite its preventive effects, HRT/E does not restore lost bone.
authors.affiliation: Department of Bioscience and Oral Diagnosis-Dentistry School, Univ Estadual Paulista "Júlio de Mesquita Filho", Campus of São José dos Campos, São José dos Campos, SP, Brazil, marianne@ict.unesp.br.
authors.forename: Marianne
authors.initials: M
authors.lastname: Spalding
authors.forename: Priscila
authors.initials: P
authors.lastname: Ferreira Amschlinger
authors.forename: Luana Marotta Reis
authors.initials: LM
authors.lastname: de Vasconcellos
authors.forename: Gabriela
authors.initials: G
authors.lastname: de Morais Gouvêa Lima
authors.forename: Warley David
authors.initials: WD
authors.lastname: Kerbauy
authors.forename: Ivan
authors.initials: I
authors.lastname: Balducci
authors.forename: Yasmin Rodarte
authors.initials: YR
authors.lastname: Carvalho
mesh_terms: D000818:Animals; D015992:Body Mass Index; D015519:Bone Density / Q000187:drug effects; D001842:Bone and Bones / Q000473:pathology; D004195:Disease Models, Animal; D004958:Estradiol / Q000008:administration & dosage; D015914:Estrogen Replacement Therapy / Q000379:methods*; D005260:Female; D010024:Osteoporosis / Q000188:drug therapy / Q000378:metabolism; D010052:Ovariectomy; D051381:Rats; D017208:Rats, Wistar; D013977:Tibia / Q000187:drug effects*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D004958:Estradiol