Suidae Pigs And Their Relatives

The pig lineage diverged earlier than the camelids, about 55 MYA.[9] PGF2a is central to the luteolytic process and can be used pharmacologically to regress pig CL to induce estrus.[3] Although pig conceptuses produce at least two forms of IFN (IFN-g and IFN-8), these appear not to be important in counteracting PGF2a but probably have a local effect on the maternal immune system.[2] Instead, the unattached elongating porcine conceptuses produce large amounts of estrogen beginning about day 10 of pregnancy.[2] Estrogen increases endometrial receptors for prolactin, which cause the uterine epithelial cells to redirect their release of PGF2a into the uterine lumen rather than basolaterally into the maternal vasculature toward the ovary and CL. Consequently, estrogen injections on days 11 to 15 of the cycle can induce a prolonged pseudopregnancy.[5] PGE2 is also produced and may act as a luteoprotective/luteotrophic agent.[2] Doubts remain, however, as to whether the estrogen-based mechanism is the sole mechanism that prevents luteolysis in the pig.[12]

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