Roberts R M, Raub T J, Bazer F W
Fed Proc. 1986 Sep;45(10):2513-8.
The pig possesses a noninvasive, diffuse type of epitheliochorial placentation in which the blood supply of the mother is well separated from the absorptive surface of the chorion, a feature that must complicate the movement of nutrient molecules across the placenta. Evidence is presented that a protein synthesized and secreted by the glandular epithelial cells of the maternal uterus of the pig is involved in iron transport to the fetus. This protein, uteroferrin, is induced by progesterone; is purple, which results from an unusual iron center; and possesses acid phosphatase activity. Secreted uteroferrin is taken up by specialized chorionic epithelial cells located in domed structures, called areolae, overlying the mouth of each uterine gland. Uteroferrin then enters the placental venous drainage and its iron is efficiently incorporated into fetal hemoglobin. It is taken up by the fetal liver or cleared by the kidney. The liver is the main site of erythropoiesis in the fetus. From the kidney uteroferrin enters the allantoic sac where it exchanges its iron with fetal transferrin. The rate of uteroferrin biosynthesis in the uterus and its rate of metabolism in the fetus can theoretically provide sufficient iron for the needs of pregnancy, at least until around day 70 of the 115-day gestation. Uteroferrin and transferrin, the iron transport protein of plasma, appear to be unrelated proteins.
猪具有一种非侵入性的弥漫型上皮绒毛膜胎盘，在这种胎盘中，母体的血液供应与绒毛膜的吸收表面分隔良好，这一特征必然会使营养分子穿过胎盘的过程变得复杂。有证据表明，猪母体子宫腺上皮细胞合成并分泌的一种蛋白质参与了铁向胎儿的转运。这种蛋白质，即子宫铁蛋白，由孕酮诱导产生；呈紫色，这是由一个不寻常的铁中心导致的；并且具有酸性磷酸酶活性。分泌的子宫铁蛋白被位于穹顶状结构（称为乳晕）中的特化绒毛膜上皮细胞摄取，这些乳晕覆盖在每个子宫腺口上方。然后子宫铁蛋白进入胎盘静脉引流，其铁被有效地整合到胎儿血红蛋白中。它被胎儿肝脏摄取或被肾脏清除。肝脏是胎儿红细胞生成的主要部位。子宫铁蛋白从肾脏进入尿囊，在那里它与胎儿转铁蛋白交换铁。理论上，子宫中铁蛋白的生物合成速率及其在胎儿体内的代谢速率能够为孕期需求提供足够的铁，至少在115天妊娠期的第70天左右之前是这样。子宫铁蛋白和血浆中的铁转运蛋白转铁蛋白似乎是不相关的蛋白质。
