Administration of a gonadotropin-releasing hormone antagonist to mares at different times during the luteal phase of the estrous cycle

作者：Evans Margaret J^*; Alexander Susan L; Irvine Clifford H G; Kitson Niere E; Taylor T Bruce

来源：Animal Reproduction Science, 2011, 127(3-4): 188-196.

DOI：10.1016/j.anireprosci.2011.07.020

• GnRH
• Antagonist
• Gonadotropins
• Progesterone
• Ovulation
• Mare

The GnRH antagonist cetrorelix was given during the early (Days 1-5), mid (Days 6-10 or 5-12) or for the entire (Days 1-16) luteal phase of mares to inhibit the secretion of FSH and LH (Day 0 = ovulation). Frequent blood sampling from Day 6 to Day 14 was used to determine the precise time-course of the suppression (cetrorelix given Days 6-10). Cetrorelix treatment caused a decrease in FSH and LH concentrations by 8 and 16 h, respectively, and an obliteration of the response to exogenous GnRH given 24 h after treatment onset. Treatment never suppressed gonadotropin concentrations to undetectable levels; e.g. frequent sampling showed that the nadirs reached in FSH and LH were 46.2 +/- 6% and 33.1 +/- 11%, respectively, of pre-treatment concentrations. Daily FSH concentrations were decreased in all treatment groups but daily LH concentrations were lower only when treatment commenced at the beginning of the luteal phase: progesterone concentrations depended on the time of cetrorelix administration, but the changes suggested a role for LH in corpus luteum function. The inter-ovulatory interval was longer than controls when cetrorelix was given in the mid- or for the entire luteal phase, but was unaffected by treatment in the early phase. Nevertheless, in all groups, FSH concentrations were higher (P < 0.05 when compared to Day 0, subsequent ovulation) approximately 6-10 days before this next ovulation. This consistent relationship suggests a stringent requirement for a GnRH-induced elevation of FSH above a threshold at, but only at, this time; i.e. approximately 6-10 days before ovulation.

• 出版日期2011-9