Uterine Protein Secretions: Relationship to Development of the Conceptus

Abstract

Proteins in uterine secretions have been studied in a variety of species since proteins are known to serve as enzymes, carrier molecules and possible regulators of genetic activity (histone and nonhistone chromosomal proteins). The data presented herein deal specifically with proteins isolated from the uterine lumen of the non-pregnant pigs and fetal fluids of pregnant gilts. Proteins having acid phosphatase, leucine aminopeptidase, lysozyme, cathepsin and nonspecific esterase enzymatic activity have been detected. Futhermore, two different size classes of proteins have been shown to bind H3 -progesterone, but not tritium labeled estradiol, estrone or prostaglandin F2α Proteins having these same enzymatic and progesterone binding properties have been found in allantoic fluid from pregnant gilts between 30 and 100 days of gestation. Results of immunofluorescent antibody studies designed to determine the site of synthesis, movement and localization of the porcine purple acid phosphatase suggest that: (1) these proteins are maternal in origin; (2) the proteins are synthesized and secreted by the uterine endometrial surface and glandular epithelium and (3) the proteins are absorbed via the placental areolae, transported across the chorio-allantois membranes and sequestered in the allantoic fluid. Passive immunization of gilts against the purple intra-uterine protein resulted in a reduction in placental development. On the other hand, progesterone therapy designed to increase uterine protein secretions stimulated placental development through increased placental length and allantoic fluid volume. The latter effect may have resulted from an increased rate of conversion of progesterone to estrogens since water transport is an estrogen related phenomenon. In general, the available data suggest that uterine protein secretions may affect placental development primarily and embryonic/fetal development only secondarily.