Role of uteroferrin in iron transport and macromolecular uptake by allantoic epithelium of the porcine conceptus.
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abstract
Uteroferrin (UF) is an iron-containing, progesterone-induced glycoprotein present in allantoic fluid and uterine secretions of swine between Days 30 and 105 of gestation. The role of UF in maternal-to-fetal iron transport and uptake of macromolecules 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 Ci 59Fe injected intravenously. Twenty-four h after the 59 Fe 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 allantoic fluid by carboxymethyl cellulose (CMC) ion exchange chromatography. In Experiment 2, macromolecular uptake by the 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 incubated in minimal essential medium (MEM) containing 1 of the following proteins labeled with fluorescein isothiocyanate (FITC): FITC--globulin; FITC-uteroferrin; FITC-transferrin or FITC--globulin with 10-4M Na-arsenite. Uptake of these proteins by chorion and allantois, but not amnion was observed. The Na-arsenite inhibited protein uptake. When FITC--globulin was introduced into the allantoic fluid on Day 60 of pregnancy, uptake by the allantois was observed. Results of this study support the concept that uteroferrin (UF) plays a major role in iron transport to the conceptus. In addition, data indicate that the allantoic epithelium is capable of transporting proteins normally found in allantoic fluid, i.e., uteroferrin and transferrin, as well as a protein not normally found in either fetal serum or allantoic fluid, i.e., -globulin. Failure to detect uptake of these proteins when Na-arsenite was added to the incubation medium suggests that transport of these proteins is by an active process.
