Studies on the Luteal Function in the Late Pregnant Cow
Pimentel, Claudio Alves
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https://hdl.handle.net/2142/71291
Description
Title
Studies on the Luteal Function in the Late Pregnant Cow
Author(s)
Pimentel, Claudio Alves
Issue Date
1982
Department of Study
Veterinary Medical Science
Discipline
Veterinary Medical Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Veterinary Science
Abstract
Corpora lutea (CL) from cows at 270 (5) or 250 (5) days of gestation were incubated with LH or cAMP. CL of cows at 250 days had increased progesterone accumulation in response to LH and cAMP while the group at 270 days did not respond to LH. Higher plasma concentrations of estrogens were found in the group at 270 days pregnant however progesterone and PGFM were not different among groups. In a second experiment, 8 cows at 245 days of gestation received intravenous infusion of estrone or vehicle during 5 days. CL were removed at 120 hours after the beginning of the infusion for in vitro incubations with LH and cAMP. Estrone infusion caused an increase in the concentrations of unconjugated estrone, and unconjugated and conjugated estradiol-17B in plasma but no change occurred in conjugated estrone, progesterone, cortisol, PGF2a, PGFM and LH concentrations. In vitro luteal function was not affected by estrone infusion. However, maximal luteal response was correlated with pre-infusion concentrations of conjugated estrogens suggesting a negative association between endogenous conjugated estrone and luteal function. The third experiment was undertaken after the lutectomy following estrone or vehicle infusion in experiment 2. PGF2a was estimated in the uterine vein, PGFM in the carotid artery and progesterone in both sampling sites. Higher concentrations of progesterone as well as a slower rate of progesterone decline were observed in the uterine vein than in the carotid artery. These results indicated that the placenta is an active source of progesterone at 250 days of gestation. The high plasma concentrations of estrogens induced by estrone did not affect placental production of progesterone. No changes over time were observed in PGF2a and PGFM concentrations after lutectomy in both groups. However, plasma concentrations of PGF2a were higher in the estrone-infused group than in the control group.
From the present study, it can be concluded that, although the high prepartum concentrations of estrogens are not the cause of luteolysis, they might reflect placental maturation being associated with decreased prepartum luteal function. The withdrawal of placental progesterone output at 270 days of gestation might be due to increased estrogen synthesis from progesterone as substrate which in turn would contribute to the change in estrogen:progesterone ratio necessary for PGF2a secretion and subsequent luteolysis.
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