Evidence that progesterone may influence subsequent luteal function in the ewe by modulating preovulatory follicle development.
Ovulation was induced in seasonally anoestrous ewes by repeated 2-h injections of 250 ng Gn-RH, after 12 days (Group 1, N = 7; Group 2, N = 8), 2 days (Group 3, N = 8) or no (Group 4, N = 7) progesterone pretreatment. A preovulatory LH peak occurred spontaneously at a mean (+/- s.e.m.) time of 43.1 +/- 2.0 h, 38.5 +/- 3.1 h and 26.8 +/- 1.7 h after the start of Gn-RH treatment in Groups 1, 3 and 4 respectively, and was artificially induced in ewes in Group 2, after 24 h of treatment, by a single i.v. injection of 150 micrograms Gn-RH. Normal luteal function occurred in all progesterone-pretreated ewes, but in only 1/7 animals not treated with progesterone. These results demonstrate that, although normal luteal function in progesterone-primed ewes induced to ovulate with repeated injections of low doses of Gn-RH is associated with a delayed preovulatory LH peak, it is not this extended period of follicle development which is responsible for functional competence of the resultant corpus luteum. Since as little as 2 days of exposure to elevated plasma progesterone concentrations is effective, it is suggested that progesterone may act directly on the preovulatory follice.
D000818:Animals; D003338:Corpus Luteum / Q000502:physiology*; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000187:drug effects* / Q000254:growth & development; D010060:Ovulation / Q000187:drug effects; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D012756:Sheep
D010906:Pituitary Hormone-Releasing Hormones; D011374:Progesterone; D007986:Luteinizing Hormone