Prostaglandin F2α as the Luteolysin in Swine: VI. Hormonal Regulation of the Movement of Exogenous PGF2α from the Uterine Lumen into the Vasculature1

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Abstract
To test the endocrine-exocrine theory of maternal recognition of pregnancy in the pig 16 gilts were assigned randomly to a 2 .times. 2 factorial involving pretreatment with sesame oil (SO) or estradiol valerate (5 mg; EV) injected on Days 11 through 14 of the estrous cycle and an intrauterine injection of saline (5 ml; SA) or prostaglandin F2.alpha. (50 .mu.g; PGF) on Day 14. Peripheral blood samples were collected for 120 min postinjection and analyzed for 15-keto-13,14-dihydro-PGF2.alpha. (PGFM). PGFM concentrations were lower in EV than SO gilts (438 vs. 844 pg/ml; p < 0.05). There was heterogeneity of regression between EV and SO gilts (p < 0.01), with EV gilts having a slower release of PGF from the uterine lumen into the vasculature. Prostaglandin F2.alpha. did not increase mean PGFM concentrations (p > 0.10), but resulted in an altered temporal pattern of PGFM (p < 0.05) compared to SA gilts. There was an interaction between the two treatments over time, with EV-PGF gilts demonstrating a slower, more graudal release of PGFM than SO-PGF gilts. To test whether prostaglandins of the E series were involved in this mechanism, gilts were assigned to two 4 .times. 4 latin squares balanced for residual effects and treated with saline or flunixen meglumine (Banamine). Each gilt was treated with four PGE:PGF infusion sequences (SEQ) in each uterine born: phosphate-buffered saline (PBS; PBS-SEQ), PGE1 (50 .mu.g), PGE2 (50 .mu.g), and PGE1 (25 .mu.g) + PGE2 (25 .mu.g) (PGE-SEQ), with each infusion followed 15 min later by PGF (25 .mu.g). Peripheral blood samples were analyzed for PGFM. Heterogeneity of regression between the two blocks was not detected (p > 0.10). Banamine lowered both mean PGFM concentrations (p < 0.10; 1001 vs. 357 pg/ml) and variance (p < 0.05). Mean PGFM concentrations were greater post-PGF (P < 0.05) both post-PGE1 and post-PGE2. There was heterogeneity of regression between the 2 sets of Sequences (p < 0.05) and were increased in PGE-SEQ versus PBS-SEQ (p < 0.01). These data indicate that estrogens act on the porcine endometrium to reduce rate of movement of PGF2.alpha. from the uterine lumen into the vasculature, but prostaglandins E1 and E2 do not appear to be responsible for this estrogen-mediated effect.

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