Progesterone-Induced Uterine Secretions in Pigs. Recovery from Pseudopregnant and Unilaterally Pregnant Gilts

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Abstract
Gilts were rendered either pseudopregnant, by injection of 5 mg estradiol valerate daily from days 11 to 15 of an estrous cycle, or unilaterally pregnant by one of two methods. In the first, embryos were flushed from one uterine horn on day 18 of pregnancy. Alternatively, one uterine horn was ligated prior to breeding the animal and estradiol valerate (5mg/day) was administered from days 11 to 15 to prevent the luteolytic effect of the nongravid uterine horn. At either day 60 or 70 of pregnancy or pseudopregnancy each uterine horn of the pseudopregnant gilts and the nongravid horn of unilaterally pregnant gilts were flushed with saline to recover protein. No significant differences were found for the amount of protein or uteroferrin (purple protein) recovered per horn in the uterine flushings from pseudopregnant or unilaterally pregnant gilts. In both groups, the content of uteroferrin was higher at Day 60 than at Day 70 and ligation of a uterine horn did not lead to improved recovery of either protein or uteroferrin. The amounts of protein recovered per horn from unilaterally pregnant and pseudopregnant animals were comparable to those obtained from ovariectomized gilts administered progesterone daily for up to 60 days. Polypeptides from the three groups of flushings were examined by two dimensional electro-phoretic analysis and shown to contain a similar group of polypeptides. In particular, four low molecular weight, acidic polypeptides and several basic species, including uteroferrin and lysozyme were identified which were not present in ovariectomized animals administered either corn oil alone or corn oil plus estradiol valerate. Because of the relative ease of preparation, pseudopregnant gilts are recommended as the best source of progesterone-induced uterine protein secretions.