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Biology of Reproduction, Vol 13, 126-135, Copyright © 1975 by Society for the Study of Reproduction

Failure of Prostaglandin F2agr to Cause Luteal Regression in Ewes After Destruction of Ovarian Follicles by X-Irradiation

JAMES E. HIXON 1, DENNIS R. GENGENBACH 1, , and WILLIAM HANSEL 1

1 Department of Animal Science, Cornell University, Ithaca, New York 14853


The hypothesis that estradiol-17beta may play a role in prostaglandin F2agr (PGF2agr)-induced luteolysis was tested in ewes following selective destruction of ovarian follicles by X-irradiation. The effects of two injections of (1) 7 mg PGF2agr, (2) 750 µg estradiol benzoate (E2 B) and (3) 7 mg PGF2agr + 750 µg E2 B were compared in sham and X-irradiated ewes. Treatment of sham-irradiated ewes with PGF2agr resulted in luteolysis in all 5 treated ewes, as judged by a fall in the plasma progesterone concentration to non-detectable levels (<0.2 ng/ml) by 54 h after the first injection. In contrast, luteolysis was not observed in 4 of 5 X-irradiated ewes following treatment with PGF2agr, as indicated by plasma progesterone levels greater than 1.60 ng/ml 96 h after the first injection and corpus luteum weights in excess of 535 mg. Luteolysis was observed in the fifth animal of this group, ewe #20, in which plasma progesterone fell to non-detectable levels and a corpus luteum of 203 mg was observed at autopsy. The mean plasma estradiol concentration ranged between 4 and 9 pg/ml in sham-irradiated, PGF2agr-treated ewes, but fell to non-detectable levels before treatment with PGF2agr in all X-irradiated ewes except #20 in which levels as high as 11.6 pg/ml were observed. A large luteinized, cystic follicle was observed at autopsy in ewe #20. These observations suggest that destruction of ovarian follicles to remove the primary source of estradiol reduced the effectiveness of PGF2agr as a luteolytic agent.

Treatment of both sham and X-irradiated animals with E2 B was luteolytic, although the mean plasma progesterone concentrations were not depressed (P<0.05) below control levels until 54 and 60 h after the first injection. Treatment of sham and X-irradiated ewes with E2 B + PGF2agr was also luteolytic and plasma progesterone concentrations were significantly reduced below control levels 1 and 12 h after treatment in sham and X-irradiated groups, respectively. The combined treatment of E2 B + PGF2agr therefore resulted in a significant reduction in progesterone concentration much earlier than observed after either treatment alone. These results indicate that estradiol potentiated the luteolytic action of PGF2agr in sheep.

 Submitted on February 21, 1975
Accepted on April 9, 1975






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Copyright © 1975 by the Society for the Study of Reproduction.