title: A bovine model for examining the effects of an aromatase inhibitor on ovarian function in women.
abstract: OBJECTIVE
  To test the hypothesis that treatment with an aromatase inhibitor (letrozole) will terminate dominant ovarian follicle growth and result in the emergence of a new follicular wave, regardless of the stage of follicular development at the time of treatment.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Academic research center.
  
  
  METHODS
  Postpubertal beef heifers.
  
  
  METHODS
  Randomized trial involving treatment with letrozole on days 1-3, 3-5, 5-7 (day 0 = pretreatment ovulation) or no treatment.
  
  
  METHODS
  Follicular development, corpus luteum (CL) development, hormone profiles, and plasma aromatase inhibitor concentration.
  
  
  RESULTS
  Multiple doses of letrozole lengthened the period of follicular dominance, delayed emergence of the next follicular wave, and resulted in a larger CL regardless of the stage of the follicular wave in which treatments were initiated. No effects on circulating FSH concentrations were detected, but the stimulatory effects on the dominant follicle and CL were associated with increased plasma concentrations of LH in letrozole-treated animals. Plasma P concentrations were numerically higher throughout the luteal phase in letrozole-treated versus control heifers, but differences were not significant.
  
  
  CONCLUSIONS
  The results provide rationale for the hypothesis that the mechanism of action responsible for the stimulatory effect of aromatase inhibitors on ovarian function involves an elevation in circulating concentrations of LH rather than FSH.
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Jimena
authors.initials: J
authors.lastname: Yapura
authors.forename: Reuben J
authors.initials: RJ
authors.lastname: Mapletoft
authors.forename: Roger
authors.initials: R
authors.lastname: Pierson
authors.forename: Jaswant
authors.initials: J
authors.lastname: Singh
authors.forename: Jonathan
authors.initials: J
authors.lastname: Naile
authors.forename: John P
authors.initials: JP
authors.lastname: Giesy
authors.forename: Gregg P
authors.initials: GP
authors.lastname: Adams
mesh_terms: D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D047072:Aromatase Inhibitors / Q000008:administration & dosage* / Q000097:blood; D015415:Biomarkers / Q000097:blood; D002417:Cattle; D003338:Corpus Luteum / Q000187:drug effects; D004334:Drug Administration Schedule; D004958:Estradiol / Q000097:blood; D030762:Estrous Cycle / Q000097:blood / Q000187:drug effects*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D000077289:Letrozole; D007986:Luteinizing Hormone / Q000097:blood; D023421:Models, Animal; D009570:Nitriles / Q000008:administration & dosage* / Q000097:blood; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000201:enzymology; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000201:enzymology; D011374:Progesterone / Q000097:blood; D013997:Time Factors; D014230:Triazoles / Q000008:administration & dosage* / Q000097:blood; D014463:Ultrasonography
chemical_list: D047072:Aromatase Inhibitors; D015415:Biomarkers; D009570:Nitriles; D014230:Triazoles; D011374:Progesterone; D004958:Estradiol; D000077289:Letrozole; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D001141:Aromatase