Source of Foetal Iron in the Cat

Abstract

Summary. The transfer of iron from maternal blood to the foetuses was determined from the uptake of Bopg by the foetuses found 24 hours after the intravenous injection of ^OFe-labelled plasma or erythrocytes into pregnant cats in the last one-third of pregnancy. A mean value of 2-7 ng Fe was transferred from maternal plasma, whereas 176 ng was transferred from erythrocytes. It was concluded that the major source of foetal iron in the cat is maternal erythrocytes, and that transfer from maternal plasma is quantitatively insignificant. INTRODUGTION.In animals with the haemochorial type of placenta the rate of iron transfer across the placenta from maternal plasma is sufficient to account for all iron accumulated by the foetus (Vosburgh and Flexner, 1950;Bothwell, Pribilla, Mebust and Finch, 1958;Glasser, Wright and Heyssel, 1968;Fletcher and Suter, 1969;Seal, Sinha and Doe, 1972). Hence, it has been concluded that, in animals with haemochorial placentas, iron is transferred directly from the plasma iron-carrying protein, transferrin, to the placenta and thence to the foetal circulation. By contrast, however, in animals vvith endotheliochorial types of placenta the rate of iron transfer from maternal plasma to foetuses found using plasma transferrin-bound 59pg g^ a tracer was much less than that required for foetal needs (Seal et al, 1972;Baker and Morgan, 1973). This was probably due to the fact that the majority of the iron transferred to the foetuses was derived from a source other than maternal plasma transferrin, most likely maternal erythrocytes; but it may have resulted from delayed transfer of iron across the placenta. These possibilities were investigated in the present experiments performed in the cat which has an endotheliochorial type of placenta. Iron-59 was used as a tracer. It was administered to the pregnant animals in two forms, either bound to plasma transferrin or incorporated into erythrocytes. Iron uptake by the placentas, foetal membranes and foetuses was calculated from the 50Fe found in these tissues 24 h after the injections. MATERIALS AND METHODS.Pregnant cats in the latter one-third of pregnancy were used. The gestation age was estimated from the foetal weight (Goronios, 1933).Plasma transferrin-bound ^^Fe was obtained by incubating freshly obtained cat plasma with ssFeGlg for 1 h, with care that the amount of iron added to the plasma did not exceed 50% of its iron-binding capacity. Erythrocytes labelled with sopg were obtained from nonpregnant donor cats which had been injected intraperitoneally with isotonic 59Fe-ferric citrate 4-7 days prior to bleeding from a radial vein, using heparin as an anticoagulant. The cells were washed twice with cold 0-15M NaGI.

Sequential Changes in Erythrocyte Volume Distribution and Microcytosis Associated with Iron Deficiency in Kittens

“…Iron supplementation in queens either before or after birth would likely be of no value. In cats, maternal transfer of iron in utero principally involves extravasation of maternal erythrocytes into the uterus and is independent of serum iron values [26]. Furthermore, maternal iron supplementation had no effect on milk iron content of lactating rats and iron deficiency in their pups [15,21].…”

Fetal iron status regulates maternal iron metabolism during pregnancy in the rat

“…In pigs, for example, much of the iron delivery early in gestation comes from uteroferrin, secreted by the maternal endometrium rather than from serum transferrin (22). In other species, such as cats, the placenta is hemophagous, and obtains iron from digested maternal red cells (4,27). In general, however, for those species with a hemochorial placenta, which includes humans, rats, and rabbits, uptake is from transferrin and follows the ontogenic pattern described here and elsewhere (15).…”