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West Virginia University, Morgantown, 26506
Abstract
The responses of pregnant and nonpregnant ewes on day 13 post-estrus to a dose of prostaglandin (PG)F2
known to be luteolytic in nonpregnant ewes were compared (experiment I). Either 270 µg PGF2 THAM salt (eight nonmated and 11 mated ewes) or saline (eight nonmated and 10 mated ewes) was injected into the largest follicle on each ovary bearing a corpus luteum. Jugular plasma samples taken just prior to surgery and 4, 8, 12, 16, 20, 24, 28, 32 and 36 hr after injection were analyzed for progesterone, estradiol-17ß and luteinizing hormone (LH) by radioimmunoassay. Treatment with PGF2 shortened the estrous cycle by 1.5 days in nonmated ewes and mated ewes without embryos (P<.05). Mated ewes with embryos did not return to estrus. The linear regression of progesterone over time varied with treatment (P<.01), pregnancy status (P<.01) and treatment x pregnancy status (P<.09). Progesterone did not reach as low a level (1.3 vs .4 ng/ml; P<.05) in pregnant as in nonmated ewes. Both LH and estradiol-17ß increased in treated ewes after progesterone had decreased to approximately 50% of pre-treatment levels; the increase in estradiol was transient in the pregnant ewes. The pattern of LH did not differ with pregnancy status. It is concluded that pregnancy overcame the luteolytic effects of PGF2 (i.e., had an antiluteo-lytic effect).
Experiment II was designed to ascertain whether PGE2 has antiluteolytic properties. A catheter was inserted into each uterine horn that was ipsilateral to a corpus luteum in nonmated ewes on day 11 postestrus. Intrauterine injections of 0, 300, 600 or 900 µg of PGE2 were begun on the morning of day 12 and continued every 8 hr until estrus or day 20. Jugular plasma samples were taken just before the first injection and every 24 hr thereafter in all ewes and at .25, .5, 1, 2, 4 and 8 hr from several ewes in each group and were assayed for progesterone. The estrous cycle was lengthened and the decline in progesterone delayed by 2 days by PGE2 (P<.05). Frequent samples on day 12 did not differ in progesterone levels among treatments or over time. Prostaglandin E2 had antiluteolytic activity in ewes but no in vivo steroidogenic effect was observed.
1 Division of Animal and Veterinary Science. Supported by NICHD Contract No. 69-2215 and Hatch Project 224 (NE-72). We thank the Upjohn Company and Drs. James Lauderdale and John E. Pike for generous supplies of prostaglandins F2 and E2. The authors gratefully acknowledge assistance in surgery by James Berardinelli, Ted Smith, Greg Lewis and Roy Fogwell; and assistance in statistical analysis by Dr. W. V. Thayne. The antiserum #15 to ovine LH was generously provided by Dr. Gordon Niswender and the purified ovine LH by Dr. L. E. Reichert, Jr. The LH standard was a gift from the National Institute of Arthritis and Metabolic Disease, Bethesda, MD. Published with the approval of the Director of the Agriculture Experiment Station as Scientific Paper No. 1461.
2 West Virginia University Foundation Graduate Research Fellow.
3 Department of Obstetrics and Gynecology.
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