Relationships among progesterone, estradiol-17Î², 13, 14- dihydro-15-keto-prostaglandin F2a and prostaglandin F2a in intact ewes around the time of luteolysis
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The exact mechanisms controlling uterine secretion of prostaglandin F2Î± (PGF2Î±) 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-1S-keto-prostaglandin F2Î± (PGFM) and PGF2Î± in ewes. Experiment 1 was designed to determine whether a radioimmunoassay (RIA) for progesterone would detect pessary-released 6Î±-methyl-17Î±-hydroxy-progesterone (MPA; n=3) and oral 17Î±-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 Â± .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 PGF2Î± 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 PGF2Î±. Treatment did not affect the profiles of change in concentration of progesterone, PGFM and jugular PGF2Î±, but treatment affected (P < .05) estrogen and vena caval PGF2Î± profiles. Overall, treatment affected (P < .05) the mean concentrations of estrogen, progesterone, PGFM and PGF2Î±. sampling site (jugular vs. vena cava) affected (P < .0001) the mean concentration of progesterone, estrogen and PGF2Î±, but site did not affect PGFM concentrations. Hormonal relationships associated with changes in release of PGF2Î± were evaluated. Estrogen seemed to be the primary hormone controlling PGF2Î± 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 PGF2Î± release in ewes around the time of luteolysis.
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