Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llam
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RESEARCH
Open Access
Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llama seminal plasma Mauricio E Silva1, Juan P Smulders2, Monserrat Guerra3, Ximena P Valderrama4, Claudia Letelier2, Gregg P Adams5 and Marcelo H Ratto2*
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. Conclusion: 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.
Background In mammals, ovulation implies pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the medio-basal nuclei of the hypothalamus into the hypophyseal portal system, followed by the release of LH from the anterior pituitary into systemic circulation [1]. The classification of mammalian species as either spontaneous or induced ovulators is based on the type of * Correspondence: [email protected] 2 Instituto de Ciencia Animal, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Chile Full list of author information is available at the end of the article
stimulus responsible for eliciting GnRH release from the hypothalamus [2]. In spontaneous ovulators (e.g., cattle, sheep, goats, pigs, horses), release of
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