The exact mechanisms controlling uterine secretion of prostaglandin F₂α (PGF₂α) are not known. This study (Experiments 1, 2 and 3) was conducted to evaluate the relationships of progesterone and estrogen to changes in 13,14-dihydro-15-keto-prostaglandin F₂α (PGFM) and PGF₂α in ewes. Experiment 1 was designed to determine whether a radioimmunoassay (RIA) for progesterone would detect pessary-released 6α-methyl-17α-hydroxy-progesterone (MPA; n=3) and oral 17α-acetoxy-6-methyl-16-methylene-4, 6-pregnadiene-3, 20 dione (MGA; n=3) in blood plasma of ovariectomized ewes. Neither progestogen treatment interfered with the RIA. Experiment 2 was conducted to answer the question: Do MPA-containing pessaries delay luteolysis in intact ewes? Ewes were treated with MPA containing (n=10) or blank pessaries (controls; n=8) from d 7 and until d 18 of the estrous cycle for control and until d 22 for MPA-treated ewes; d 0 was the day of estrus. Blood samples were collected from the jugular vein throughout the experiment. Pessaries containing MPA did not affect the timing of luteolysis (d 15.4 ± .2), but they prolonged (P<.O5) the interestrous interval (17.5 d for control vs 24.1 d for MPA-treated ewes). Experiment 3 was designed to study the relationships among progesterone, estrogen, PGFM and PGF₂α in ewes. Ewes were treated with MPA-containing (n=7; 60 mg), progesterone-containing (n=8i 45 mg) or blank pessaries (n=8) from d 7 until d 20 of the estrous cycle. From d 14 and continuing until 24 h after estrus, jugular and vena caval blood samples were collected during two sampling periods daily. Plasma was assayed for progesterone, estrogen, PGFM and PGF₂α. Treatment did not affect the profiles of change in concentration of progesterone, PGFM and jugular PGF₂α, but treatment affected (P < .05) estrogen and vena caval PGF₂α profiles. Overall, treatment affected (P < .05) the mean concentrations of estrogen, progesterone, PGFM and PGF₂α. sampling site (jugular vs. vena cava) affected (P < .0001) the mean concentration of progesterone, estrogen and PGF₂α, but site did not affect PGFM concentrations. Hormonal relationships associated with changes in release of PGF₂α were evaluated. Estrogen seemed to be the primary hormone controlling PGF₂α release. In conclusion, MPA treatment did not delay the timing of luteolysis, but it increased the interestrous interval. Of the compounds measured, estrogen accounted for the greatest proportion of the variation in PGF₂α release in ewes around the time of luteolysis. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/46031 |
| Date | 25 November 2009 |
| Creators | Fortin, Suyapa |
| Contributors | Animal Science, Lewis, Gregory S., Hohenboken, William D., Knight, James W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | viii 85 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 25120057, LD5655.V855_1991.F679.pdf |
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