Evidence that progesterone may influence subsequent luteal function in the ewe by modulating preovulatory follicle development

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Authors:
B. J. McLeod
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W. Haresign
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DOI:
https://doi.org/10.1530/jrf.0.0710381
Volume/Issue:
Volume 71: Issue 2
Page Range:
381–386
Article Type:
Research Article
Online Publication Date:
Jul 1984
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Summary. 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 μg 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.

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Print ISSN:
1470-1626
Online ISSN:
1741-7899