Role of Uteroferrin in Iron Transport and Macromolecular Uptake by Allantoic Epithelium of the Porcine Conceptus1, 2

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Abstract
Uteroferrin (UF) is an Fe-containing, progesterone-induced glycoprotein present in allantoic fluid and uterine secretions of swine between days 30-105 of gestation. The role of UF in maternal to fetal Fe transport and uptake of macrolecules by allantoic epithelium were studied in 2 experiments. In experiment 1, 8 pregnant gilts were assigned to treatment on either day 30, 60, 90 or 105 of gestation. Three additional gilts were rendered unilaterally pregnant and assigned to treatment on day 60. All gilts received 100 .mu.Ci 59Fe i.v., 24 h after the 59Fe treatment, gilts were hysterectomized and fetal fluids and tissues collected. Uterine flushings were also collected from the nongravid uterine horn of unilaterally pregnant gilts. Fetal bone, spleen liver, kidney and placenta accumulated 59Fe, but fetal spleen was the only tissue in which total 59Fe accumulation was affected (P < 0.05) by day of gestation. Radiolabeled UF was also isolated from uterine flushings (14 cpm/mg protein) and from concentrated allantotic fluid by CM cellulose ion exchange chromatography. In experiment 2, macromolecular uptake by allantoic epithelium, both in vitro and in vivo, was examined. Sections of allantois, chorion, amnion and fetal gut (FG) were collected from day-60 pregnant gilts. Samples of each of the tissues were indubated in minimal essential medium (MEM) containing 1 of the following proteins labeled with fluorescein isothiocyanate (FITC): FITC-.gamma.-globulin; FITC-UF; FITC-transferrin or FITC-.gamma.-globulin with 10-4 M sodium arsenite. Uptake of these proteins by chorion and allantois, but not amnion, was observed. The sodium arsenite inhibited protein uptake. When FITC-.gamma.-globulin was introduced into the allantoic fluid on day 60 pregnancy, uptake by the allantois was observed. UF plays a major role in Fe transport to ther conceptus. The allanoic epithelium is evidently capable of transporting proteins normally found in allantoic fluid, i.e., UF and transferrin, as well as a protein not normally found in either fetal serum or allantoic fluid, i.e., .gamma.-globulin. Failure to detect uptake of these proteins when sodium-arsenite was added to the incubation medium suggests that transport of these proteins is by an active process.

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