Role of progesterone in regulating uteroovarian venous concentrations of PGF 2 α and PGE 2 during the estrous cycle and early pregnancy in ewes

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The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F 2 α (PGF 2α) and E 2 (PGE 2) during days 13 to 16 of the ovine estrous cycle or early pregancy was examined. At estrus, ewes were either mated to a fertile ram or unmated. On day 12 postesturus, ewes were laparotomized and a catheter was inserted into a uteroovarian vein. Six mated and 7 unmated ewes received no further treatment. Fifteen mated and 13 unmated ewes were ovariectomized on day 12 and of these, 7 mated and 5 unmated ewes were given 10 mg progesteron sc and an intravaginal pessary containing 30 mg of progesterone. Uteroovarian venous samples were collected every 15 min for 3 h on days 13 to 16 postestrus. Mating resulted in higher mean daily concentrations of PGE 2 in the uterovarian vein than in unmated ewes. Ovariectomy prevented the rise in PGE 2 with day in mated ewes but had no effect in unmated ewes. Progesterone treatment restored PGE 2 in ovariectomized, mated ewes with intact embros. Mating had no effect on mean daily concentrations of PGF 2α or the patterns of the natural logarithm (ln) of the invariance of PGF 2α. Ovariectomy resulted in higher mean concentrations and ln invariances of PGF 2α on day 13 and lower mean concentrations and ln invariances of PGF 2α on days 15 and 16. Replacement with progesterone prevented these changes in patters of mean concentrations and ln variances of PGF 2α following ovariectomy. It is concluded that progesterone regulates the release of PGF 2α from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF 2α which are seen with falling concentrations of progesterone. This occurs in both pregnant and non-pregnant ewes. Progesterone is also needed to maintain increasing concentrations of PGE 2 in mated ewes.