title: Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llama seminal plasma.
abstract: BACKGROUND
  The purpose of the study was to determine if the effect of llama OIF on LH secretion is mediated by stimulation of the hypothalamus or pituitary gland.
  
  
  METHODS
  Using a 2-by-2 factorial design to examine the effects of OIF vs GnRH with or without a GnRH antagonist, llamas with a growing ovarian follicle greater than or equal to 8 mm were assigned randomly to four groups (n = 7 per group) and a) pre-treated with 1.5 mg of GnRH antagonist (cetrorelix acetate) followed by 1 mg of purified llama OIF, b) pre-treated with 1.5 mg of cetrorelix followed by 50 micrograms of GnRH, c) pre-treated with a placebo (2 ml of saline) followed by 1 mg of purified llama OIF or d) pre-treated with a placebo (2 ml of saline) followed by 50 micrograms of GnRH. Pre-treatment with cetrorelix or saline was given as a single slow intravenous dose 2 hours before intramuscular administration of either GnRH or OIF. Blood samples for LH measurement were taken every 15 minutes from 1.5 hours before to 8 hours after treatment. The ovaries were examined by ultrasonography to detect ovulation and CL formation. Blood samples for progesterone measurement were taken every-other-day from Day 0 (day of treatment) to Day 16.
  
  
  RESULTS
  Ovulation rate was not different (P = 0.89) between placebo+GnRH (86%) and placebo+OIF groups (100%); however, no ovulations were detected in llamas pre-treated with cetrorelix. Plasma LH concentrations surged (P < 0.01) after treatment in both placebo+OIF and placebo+GnRH groups, but not in the cetrorelix groups. Maximum plasma LH concentrations and CL diameter profiles did not differ between the placebo-treated groups, but plasma progesterone concentrations were higher (P < 0.05), on days 6, 8 and 12 after treatment, in the OIF- vs GnRH-treated group.
  
  
  CONCLUSIONS
  Cetrorelix (GnRH antagonist) inhibited the preovulatory LH surge induced by OIF in llamas suggesting that LH secretion is modulated by a direct or indirect effect of OIF on GnRH neurons in the hypothalamus.
authors.affiliation: Escuela de Medicina Veterinaria, Facultad de Recursos Naturales, Universidad Católica de Temuco, Temuco, Chile.
authors.forename: Mauricio E
authors.initials: ME
authors.lastname: Silva
authors.forename: Juan P
authors.initials: JP
authors.lastname: Smulders
authors.forename: Monserrat
authors.initials: M
authors.lastname: Guerra
authors.forename: Ximena P
authors.initials: XP
authors.lastname: Valderrama
authors.forename: Claudia
authors.initials: C
authors.lastname: Letelier
authors.forename: Gregg P
authors.initials: GP
authors.lastname: Adams
authors.forename: Marcelo H
authors.initials: MH
authors.lastname: Ratto
mesh_terms: D000818:Animals; D002161:Camelids, New World / Q000097:blood / Q000378:metabolism / Q000502:physiology; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D005299:Fertility Agents / Q000378:metabolism / Q000494:pharmacology; D005498:Follicular Phase / Q000187:drug effects* / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D006727:Hormone Antagonists / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D010060:Ovulation / Q000187:drug effects*; D010062:Ovulation Induction / Q000379:methods; D010919:Placebos; D011673:Pulsatile Flow / Q000187:drug effects; D012661:Semen / Q000378:metabolism / Q000502:physiology; D029589:Seminal Plasma Proteins / Q000378:metabolism / Q000494:pharmacology
chemical_list: D005299:Fertility Agents; D006727:Hormone Antagonists; D010919:Placebos; D029589:Seminal Plasma Proteins; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; C062876:cetrorelix