Association between uteroferrin, retinol-binding protein, and transferrin within the uterine and conceptus compartments during pregnancy in swine.

The association between uteroferrin (UF, measured as acid phosphatase [AP] activity), retinol-binding protein (RBP), and transferrin (TF), within the intrauterine environment during the estrous cycle and pregnancy was examined. Pregnant gilts were killed on Days 7, 10, 13, 16, 19, 25, 30, 40, 50, 60, 70, 80, and 90. Cyclic gilts were killed on Days 7, 10, 13, and 16. On Days 7 through 19, each uterine horn was flushed with 20 ml Minimum Essential Medium. On Days 25 through 90, serum and allantoic fluid samples were collected from each fetus within each gilt and pooled for each gilt. Uterine flushings, allantoic fluid, and fetal serum samples were assayed for AP, RBP, and TF. Endometrium was collected from all gilts and cultured with [3H]-leucine; conditioned medium was measured for nondialyzable radioactive macromolecules, AP, and RBP. In uterine flushings, AP, RBP, and TF were low on Day 7, and then increased markedly (p < 0.01) by Day 13 in both cyclic and pregnant gilts. After log transformation of the data, AP was highly correlated with RBP (r = 0.99) and TF (r = 0.91, p < 0.01). Secretion of RBP and AP by endometrium in culture also increased (p < 0.01) during this period and was similar in cyclic and pregnant gilts, and RBP and AP secretion were highly correlated (r = 0.65, p < 0.01). Endometrial tissue did not secrete detectable amounts of TF in culture. Concentrations of all three proteins were low in allantoic fluid on Day 25, after which time they increased to Day 40, and then either stabilized to Day 70 followed by a decrease to Day 90 (AP and TF) or decreased to Day 90 (RBP). Endometrial secretion of both AP and RBP increased between Day 25 and 30. Then, AP increased further to Day 40 and did not change to Day 60, while RBP did not change from Day 30 to Day 60. Both decreased from Day 60 to 70, did not change to Day 80, and then increased again to Day 90. The association of RBP and TF concentrations with AP in various maternal and conceptus compartments during pregnancy is consistent with the hypothesis that one function of these two proteins may be to protect maternal and fetal tissues from lipid peroxidation that is a possible consequence of iron transport via endometrial secretion of UF.