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Effects of Ovarian Bisection on Response to Intrafollicular Injection of PGF₂ and on Follicular Development in Ewes¹

West Virginia University, Morgantown 26506

Abstract

Transfer of prostaglandin F₂ (PGS₂) from an injected follicle to a corpus luteum (CL) in the same ovary was examined. All ewes were unilaterally-ovariectomized and the remaining ovary was either bisected and reconstructed with a latex septum or marked with India ink in the plane of bisection (sham-operated) on day-3 postestrus. An intrafollicular injection (20 µ1) was made on day 9 according to the following randomized treatments: Bisected ovary plus PGF₂ (250 ;µg) in the half of the ovary containing the CL (adjacent; four ewes) or opposite to the CL (three ewes); bisected ovary plus Tham buffer (four ewes); sham-operated plus PGF₂ (six ewes) or Tham buffer (six ewes). Length of estrous cycles (days) for ewes in which the ovary was bisected plus PGF₂ adjacent to the CL (12.1 ± 4), bisected plus PGF₂ opposite to the CL (11.5 ± .8) and sham-operated plus PGF₂ (11.9 ± 3) did not differ. However, they were shorter (P<.01) than cycles of ewes with bisected ovaries plus buffer (17.5 ± .5) or sham-operated plus buffer (16.8 ± .3). Prior to injection on day-9 postestrus, ewes with bisected ovaries had lower (P<.05) jugular venous progesterone (1.3 ± .3 ng/ml) and higher luteinizing hormone (LH; 3.3 ± 1.7 ng/ml) than ewes with sham-operated ovaries (2.7 ± .3 and .4 ± .1, respectively). Concentrations of estradiol-17ß (pg/ml) on day 9 were not different in ewes with bisected (3.4 ± .8) or sham-operated (2.7 ± .3) ovaries.

The profiles of progesterone decline over time were similar in all ewes injected with PGF₂ regardless of surgical treatment or site of injection but were not parallel to those observed in buffer-treated ewes. Concentrations of estradiol-17ß increased only when concentrations of progesterone declined to low levels following injection of PGF₂. It is suggested that PGF₂ injected into a follicle in an ovary bearing a corpus luteum is luteolytic through a local extra-ovarian pathway.

Follicles (2mm) were recorded at each laparotomy by location relative to the corpus luteum as a preliminary examination of a possible local relationship between corpora lutea and follicular development in ewes. Bisected ovaries had fewer (P<.01) total follicles and fewer follicles 2 to 5 mm than sham-operated ovaries on days 3 and 9. On day 9 there were more follicles 5 mm and greater follicular volume in the half of the ovary containing the corpus luteum (P<.05) in bisected or sham-operated ovaries. However, a greater mean follicular diameter adjacent to the CL (P<.05) was evident only in bisected ovaries on day 9. It is suggested that corpora lutea may influence follicular growth locally within the ovary.

¹ Published with the approval of the Director of the Agricultural Experiment Station as Scientific Paper No. 1449. Supported by Hatch Project 224 (NE-72). Division of Animal and Veterinary Sciences and Department of Obstetrics and Gynecology. PGF2a for injection was a gift from Dr. J. W. Lauderdale, The Upjohn Company, Kalamazoo, MI. Suggestions regarding the experimental method by Dr. O. J. Ginther, University of Wisconsin, Madison, are gratefully acknowledged.