Inadequate corpus luteum function after the induction of ovulation in anoestrous ewes by LH-RH or an LH-RH agonist

Authors:
  • AMA. S. McNeilly
    A. S. McNeilly
  • MHMorag Hunter
    Morag Hunter
  • RLR. B. Land
    R. B. Land
  • HFH. M. Fraser
    H. M. Fraser
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Abstract
Summary.: Scottish Blackface ewes were given LH-RH (3 × 30 μg i.v., at 90 min intervals) or D-Ser-(But)6-des Gly10 LH-RH ethylamide (LH-RH agonist) as a single injection (8 or 40 μg) during anoestrus. Ovulation as judged by laparoscopy occurred in 8 of the 27 animals. Despite the fact that the LH-RH agonist induced a greater release of LH and FSH the different treatments had no effect on the number of ewes ovulating and within each treatment group there was no apparent difference in the amounts of gonadotrophins released between the ewes that did or did not ovulate. All ovulations resulted in the formation of CL associated with plasma progesterone concentrations of <1 ng/ml (1–5 ng/ml in the normal luteal phase). In comparison with CL of the normal cycle the induced CL were of lower weight and had reduced progesterone content and ability to secrete progesterone in vitro. However, the binding of hCG was equivalent to that of normal CL. These results suggest that the inadequate CL formed in anoestrous ewes after a single LH-RH injection have not developed the ability to synthesize and secrete progesterone in spite of the presence of normal amounts of LH receptors.

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