Does exogenous progestogen alter the relationships among PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha, progesterone, and estrogens in ovarian-intact ewes around the time of luteolysis?
1994
Fortin, S. | Sayre, B.L. | Lewis, G.S.
The exact mechanisms controlling uterine secretion of PGF2 alpha are not known. An animal model in which progestogen concentrations are kept high and corpora lutea are allowed to regress should be useful for studying the effects of progestogen and estrogens on uterine secretion of PGF2 alpha. Thus, the primary objectives of this study with ovarian-intact ewes were to determine 1) the effect of 6 alpha-methyl-17 alpha-hydroxyprogesterone acetate (MPA) on luteal life span and changes in jugular and vena caval concentrations of PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), progesterone, and estrogens around the time of luteolysis, and 2) the relationships among changes in those compounds. The results indicate that MPA 1) reduced (P < .05) vena caval and jugular PGF2 alpha and PGFM concentrations, 2) did not affect luteal life span or progesterone concentrations, 3) increased (P < .05) jugular concentrations of estrogens, and 4) prolonged (P < .05) the interestrous interval by 7 d. Stepwise regression procedures indicated that MPA disrupted a number of the relationships among PGF2 alpha, PGFM, progesterone, and estrogens in vena caval and jugular plasma. Ovarian-intact, MPA-treated ewes may be useful for determining the mechanisms involved in controlling uterine secretion of PGF2 alpha.
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