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Effect of Injection of Progesterone into One Ovary of PMSG-Treated Anestrous Ewes on Follicle Growth and Ovarian Estradiol-17ß^1,2

University of Wisconsin, Madison 53 706

Abstract

Anestrous ewes were injected intramuscularly with an ovulatory dose of pregnant mare serum gonadotropin (1,200 IU). At the same time, each ewe was laparotomized. One ovary was injected with 10 mg of progesterone and the largest follicle on each ovary was marked. The marked follicle in progesterone-treated left ovaries grew rapidly to necropsy at 18 hr after treatment. In similarly treated ewes necropsied at 36 hr after treatment, the marked follicle in progesterone-treated left ovaries had begun to undergo atresia. The marked follicle on the contralateral (right) ovary grew less rapidly to 18 hr but continued to grow to 36 hr as did the marked follicle in both ovaries of ewes given progesterone into the right ovary.

Ovarian content of estradiol-17ß at necrospy was not significantly affected by progesterone treatment. Ovarian estradiol-17ß content was positively and significantly associated with the change in the volume of the marked follicle, laparotomy to necropsy, but was not significantly associated with the mass of the stromal tissue.

Progesterone may play a role in hastening the growth rates of follicles. The effect of progesterone on follicle growth rates does not appear to be mediated through induction or alteration of ovarian estradiol-17ß content.

¹ Research was supported by the Public Health Service Grant No. 2-T01-HD-00104-09 from the National Institute of Child Health and Human Development.

² Department of Meat and Animal Science (Paper No. 648) and Laboratory of Genetics (Paper No. 1783).

³ Present address: Animal Physiology and Genetics Institute, A.R.S., U.S.D.A., Beltsville, MD 20705.