Effect of the conceptus on quantitative and qualitative aspects of uterine secretion in pigs

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Abstract
Endometrial explants were removed from uteri of animals pregnant and pseudopregnant (5 mg estradiol valerate on (days 11-15) for 60 days, from the gravid and non-gravid horns of unilaterally pregnant pigs at (day 60 of pregnancy and from non-pregnant animals at day 12 of the estrous cycle. The tissues were cultured in the presence of L-[35S]methionine for 24 h and the tissues and medium were analyzed separately by 2-dimensional polyacrylamide gel electrophoresis. Radioactive polypeptides were identified by autoradiography of dried gels. Tissues from all except the cyclic animals released an identical group of polypeptides into the culture medium: the major radioactive products were 4 acidic polypeptides of low MW and several basic proteins, which included the purple phosphatase uteroferrin and lysozyme. Explants from 3 unilaterally pregnant pigs were cultured with L-[3H]leucine and, on a fresh weight basis, the tissue from the non-gravid horn released significantly less radioactive macromolecular material into the medium in 24 h than did tissue from gravid horns. Although the nature of the secretion produced by the pregnant uterus is a consequence of maternal hormonal regulation alone, apparently the tissue underlying a conceptus is quantitatively more active than that from unoccupied regions of a uterus.