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Biology of Reproduction, Vol 23, 1046-1053, Copyright © 1980 by Society for the Study of Reproduction
1 Division of Animal and Veterinary Sciences,
West Virginia University,
Morgantown, West Virginia 26506 Progesterone administered early in the estrous cycle of ewes decreases the average life of
corpora lutea. The effects of exogenous progesterone during estrus on patterns of concentrations
of luteinizing hormone (LH) and progesterone in peripheral plasma and of prostaglandin (PGF2 In experiment 2, ewes were injected (i.m.) with corn oil containing 0 (n = 6) or 40 mg (n = 6)
of progesterone 8 and 32 h after the onset of estrus. Beginning on Day 5, blood samples were
collected via a catheter in one utero-ovarian vein every 8 h until the onset of the next estrus for
quantification of PGF2 Decreased concentrations of LH immediately following exogenous progesterone did not interfere with the ability of the young corpus luteum to produce progesterone. Earlier peaks of PGF2
)
in utero-ovarian venous plasma were studied. In experiment 1, eight ewes received 40 mg of progesterone (i.m.) in corn oil and eight were given only corn oil 8 h after the onset of estrus (Day 0).
Mean cycle length in progesterone-treated ewes was less than in control ewes (12.5 ± 1.7 vs 16.3 ±
0.2 days: P<0.05). The concentrations of LH during and immediately following the surge were
decreased by progesterone and returned to control values by 30 h after treatment. Mean concentration of PGF2 in uterine venous plasma on Day 5 proestrus did not differ significantly between
groups.. Five of six progesterone-treated ewes had short cycles (11.0 ± 1.0 days),
while cycles averaged 17.0 ± 0.3 days for the six control ewes. Concentrations of LH were lower 8
h after the second injection of progesterone but reached control levels by 32 h. Concentrations of
progesterone in peripheral plasma of progesterone-treated and control ewes did not differ on
Days 4 to 7. The first peak of PGF2 occurred earlier in progesterone-treated (Day 8.0 ± 0.3) than
in control ewes (Day 12.3 ± 1.0; P<0.01). Analyses of the regressions of PGF2 on estradiol-17
revealed that plasma concentrations of estradiol at the same hour and at 16 and 24 h previous to
PGF2 could account for some of the variation in PGF2.
following exogenous progesterone during estrus may be more important than reduced LH in
causing earlier regression of corpora lutea.
Note:
ACKNOWLEDGMENTS
Published with the approval of the Director of the
West Virginia Agricultural and Forestry Experiment
Station as Scientific Paper No. 1616. Supported by
Hatch Project 224 (NE-72). The authors are indebted
to Dr. John Pike, The Upjohn Co., for generously
supplying PGF2 for assay standards, Dr. Lawrence
Levine, Brandeis University, for the highly specific
antiserum to PGF2, Dr. G. D. Niswender for the
ovine LH antiserum (GDN No. 15), Dr. L. E. Reichert,
Jr., for purified ovine LH (OLH-1056-C-2), and the
National Institute of Arthritis and Metabolic Diseases
for LH standard. We are grateful to Phyllis Jenkins,
Sandi Allison, and Jo Ann Silipo for their technical
assistance and to Thomas Carney for assistance with
statistical analyses.
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