PROSTAGLANDINS

CORPUS LUTEUM SUSCEPTIBILITY TO PROSTAGLANDIN F2~ (PGF2=) LUTEOLYSIS IN HYSTERECTOMIZED PREPUBERAL AND MATURE GILTS 1,3 1,4 Tony A. Puglisi ,~George B. R~npacek , Robert R. Kraeling ~ and Terry E. Kiser I iDepartment of Animal and Dairy Science, University of Georgia and 2Richard B. Russell Research Center, SEA, USDA Athens, Georgia 30602 ABSTRACT The susceptibility of induced corpora lutea (CL) of prepuberal gilts and spontaneously formed CL of mature gilts to prostaglandin F2~ (PGF2~) luteolysis was studied. Prepuberal gilts (120 to 130 days of age) were induced to ovulate with Pregnant Mare Serum Gonadotropin and Human Chorionic Gonadotropin (HCG). The day following HCG was designated as Day 0. Mature gilts which had displayed two or more estrous cycles of 18 to 22 days were used (onset of estrus = Day 0). Gilts were laparotomĀ±zed on Day 6 to 9, their CL marked with sterile charcoal and totally hysterectomized. On Day 20, gilts were injected IM with either distilled water (DW), 2.5 mg PGF2u or 5.0 mg PGF2=. An additional group of prepuberal gilts was injected with 1.25 mg PGF2~ , a dose of PGF2~ equivalent, on a per kilogram body weight basis, to the 2.5 mg PGF2~ dose given to the mature gilts. The percentages of inteal regression on Day 27 to 30 for mature and prepuberal gilts given DW, 2.5 mg PGF2~ and 5.0 mg PGF2~ were 0.0 vs 4.4, 43.5 vs 96.8 and 47.7 vs 91.6, respectively; the percentage of luteal regression for the prepuberal gilts given 1.25 mg PGF2~ was 75.1. These results indicate that induced CL of the prepuberal gilt were more susceptible to PGF2~ luteolysis than spontaneously formed CL of the mature gilt and that pregnancy failure in the prepuberal gilt could be due to increased susceptibility of induced CL to the natural luteolysin. INTRODUCTION Previously, we demonstrated that luteotropic support is adequate to maintain functional corpora lutea (CL) in the prepuberal gilt when the luteolytic mechanism is removed by complete hysterectomy. The results suggested that failure of the prepuberal gilt to maintain pregnancy following induced ovulation could be due to an imbalance between the luteolytic and luteotropic mechanisms (i). Subsequently, Puglisi et al. (2) reported that less uterine tissue was necessary to cause luteal regression in the prepuberal gilt than in the mature gilt. Two alternatives were proposed to explain pregnancy failure

3present address: College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602. 4To whom correspondence should be addressed.

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in the prepuberal gilt. First, the prepuberal gilt uterus, as compared with the mature gilt uterus, may produce an excessive amount of luteolysin that is not overcome by the luteotroplc effects of pregnancy. Second, susceptibility of the induced CL to the uterine luteolysin may be greater than that of the spontaneous CL in the mature gilt. Although not conclusive evidence, the ability of exogenous prostaglandln F2= (PGF2e) to cause luteolysis in swine (3,4,5), the temporal relationship between increasing utero-ovarian vein (UOV) plasma PGF concentrations and decreasing plasma progesterone concentrations in nonpregnant swine (6,7) and the absence of that relationship in pregnant gilts (7) indicate that PGF2e is the natural uterine luteolysln. In a previous study, Rampacek et al. (8) determined that the UOV plasma PGF concentrations were less in the unbred prepuberal gilt compared to the unbred mature gilt indicating t h a t t h e failure of the prepuberal gilt to maintain functional CL during pregnancy may not be due to a hypersecretlon of PGF into the utero-ovarlan vein. This experiment was conducted to compare the susceptibility of the induced CL in the prepuberal gilt with that of the spontaneous C L i n the mature gilt to PGF2~ luteolysis. MATERIALS AND METHODS Forty-one prepuberal crossbred gilts, 120 to 130 days of age and averaging 57 kg body weight, were induced to ovulate with an intramuscular (IM) injection of 1,000 IU Pregnant Mare Serum Gonadotropln (PMSG) followed 72 hr later by a n l M injection of 500 IU Human Chorionic Gonadotropin (HCG). Nine gilts (bred controls) were randomly selected and artificially inseminated on Day 0 (day following HCG = Day 0). Twenty-four mature crossbred gilts from the same population as the prepuberal gilts, averaging 128 kg body weight, that had exhibited two or more estrous cycles of 18 to 22 days were used in the study. All gilts, except the bred controls, were laparotomized on Day 6 to 9 (onset of estrus = Day 0 for mature gilts), their CL marked with sterile charcoal and totally hysterectomized (9). The mature gilts were randomly assigned to one of three treatments: distilled water (DW); 2.5 mg PGF2~ (free acid); 5.0 mg PGF2~. The prepuberal gilts were also randomly assigned to one of the above treatments plus an additional treatment: 1.25 mg PGF2~. The average body weight of the prepuberal gilts given 1.25 mg PGF2s was determined on the day of injection so that the amount of PGF2e administered was approximately equivalent, on a per kilogram body weight basis, to the dose administered to the mature gilts given 2.5 mg PGF2s. Prostaglandin F2~ in DW or DW vehicle was injected IM on Day 20 in a split dose at 0800 hr and 1200 hr.

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PROSTAGLANDINS Blood was obtained by anterior vena cava puncture on Days 20, 21, 22, 23 and 27 and assayed for plasma progestln concentration by radlolmmunoassay (i). All treated gilts were ovarlectomlzed on Day 27 to 30 and the ovaries examined for marked CL and marked corpora albicantla (CA). The nine prepuberal bred controls were necropsled on Day 30, their ovaries examined for CL and CA and their uteri examined for embryos. The percentages of CL regression, based on comparison between the number of CL present at Day 6 to 9 and the number of marked CL present at ovarlectomy, were converted to arc sine values and subjected to a two-way analysis of variance (ii). The progestin concentrations were subjected to log transformation (ii) and analyzed by split plot in time analysis of variance (12) and selected comparisons made by Scheffe's procedure (13). Since the only purpose of the bred controls was to insure that the population of gilts in this study were actually prepuberal, the bred controls were not included in the statistical analysis. RESULTS AND DISCUSSION At necropsy on Day 30, all nine prepuberal bred control gilts had only CA on their ovaries and no embryos were found in utero; this result indicated that this population of gilts was actually prepuberal (1,2). The average numbers of CL on Day 6 to 9, Day 27 to 30 and the percentage of luteal regression for the mature and prepuberal gilts are shown in Table i. The average number of CL on Day 6 to 9 was similar (P>.05) among treatments and between the mature and prepuberal animals. All gilts given DW maintained their CL to Day 30 except for one prepuberal gilt that had 15 marked CL and 3 marked CA. Three mature gilts given 5.0 mg PGF2a had marked CA, four had marked CL and one had both marked CA and CL; eight prepuberal gilts had marked CA and one had marked CL. Of the gilts recleving 2.5 mg PGF2e , three mature gilts had marked CA, four had marked CL and one had both marked CA and CL; all of the prepuberal gilts had marked CA at ovariectomy. Five prepuberal gilts given 1.25 mg PGF2e had marked CA and three had both marked CA and marked CL. The results of the DW treatment are similar to those previously reported for prepuberal (1,2) and mature gilts (9) and demonstrate that total hysterectomy maintains CL in both mature and prepuberal gilts until at least Day 30. There was no difference (P>.05) in the percentage of luteal regression between mature and prepuberal gilts receiving DW; however, the percentage of luteal regression was lower (P.05) between mature gilts given 2.5 mg and 5.0 mg PGF2e. In addition, the percentage of luteal regression was similar (P>.05) between prepuberal gilts receiving 1.25, 2.5 and 5.0 mg PGF2~. In contrast, the percentage of luteal regression was higher (P

Corpus luteum susceptibility to prostaglandin F2 alpha (PGF2 alpha) luteolysis in hysterectomized prepuberal and mature gilts.

PROSTAGLANDINS CORPUS LUTEUM SUSCEPTIBILITY TO PROSTAGLANDIN F2~ (PGF2=) LUTEOLYSIS IN HYSTERECTOMIZED PREPUBERAL AND MATURE GILTS 1,3 1,4 Tony A. Pu...
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