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Preovulatory Changes in Prostaglandins E₂ and F₂ in Ovine Follicles^1,2,

West Virginia University³, Morgantown 26506

Abstract

In the first of three experiments aimed at elucidating preovulatory changes in follicular prostaglandin E₂ (PGE₂) and protaglandin F₂ (PGF₂), ovarian follicles were collected from ewes 12 hr before and two times during estrus (twice-daily observations). Content of PGE₂ in the largest follicle was greater (P<.05) at the first detection of estrus than 12 hr before the expected onset of estrus, then tended to decline (P<.1) by 12 hr later, but was still higher (P<.05) than in preestrual follicles. Content of PGF₂ in these follicles increased (P<.05) with time. In the second largest follicle, content of PGE₂ tended to be higher (P<.1) during the early stage of estrus. Differences among levels of prostaglandins in smaller follicles were not significant. In the second study, ewes were checked for estrus, and peripheral plasma to be assayed for luteinizing hormone (LH) was taken at 4-hr intervals beginning on day 15 of the cycle. Ovarian venous effluent was collected, and the preovulatory follicles were separated into tissue and fluid components at 0, 4, 8, 12, 16 and 20 hr after the onset of estrus. Data were standardized to the first detected increase in LH. Content of cyclic AMP increased (P<.05) in the follicular wall by 4 hr after the initiation of the surge of LH. By 8 hr, contents of PGE₂ and PGF₂ had increased (P<.05). In tissues dissected at 16 to 20 hr, contents of PGE₂ and cyclic AMP had declined (P<.05) from levels observed in tissues dissected at 12 hr, while PGF₂ remained elevated. Changes in prostaglandins in the follicular wall were not reflected in follicular fluid or ovarian venous plasma. In the third experiment, the largest follicle was injected with saline or an ovulatory dose of gonadotropin (5 µg) on day 15, and the layers of the follicular wall were seaprated 8 hr later. Both LH and follicle stimulating hormone increased (P<.05) the content of PGE₂ in the granulosa and the theca. Content of PGF₂ in the granulosal layer was low and not affected by treatment. Thecal content of PGF₂ was higher (P<.05) ingonadotropin-treated follicles. Observed changes in PGE₂ and PGF₂ in the preovulatory ovine follicle provide support for the concept that prostaglandins function in the ovulatory mechanism.

¹ Published with the approval of the Director of the West Virginia Agr. Exp. Sta. as Scientific Paper No. 1654.

² The authors gratefully acknowledge Dale Coleman, Ann Connor, Dan Deaver, Cathy Gust, Joe Ottobre, Bruce Pratt, Char Sheffel and Bill Silvia for their assistance in surgery, and Phyllis Jenkins for her technical assistance in the laboratory.

³ Div. of Anim. and Vet. Sci.