A previous study in sheep and monkeys showed that maternal EPO does not cross the placenta, so it is unlikely that circulating EPO originates from a maternal source. A recent study of human placenta indicated that immunoreactive EPO as well as EPO mRNA was present in the human trophoblast, raising the interesting possibility that the porcine placenta may produce EPO as well. Further study of the expression of EPO mRNA and protein in the pig will be required to identify the source of circulating fetal EPO. birth control pills
Differential Cell Counts of Erythroid Precursors in Fetal Blood
The dramatic changes in erythroid precursor populations and the 10-fold increase in RBC concentrations seen in this study are compelling evidence of the critical nature of this time period (Day 24-Day 40) in the development of the erythron. The percentage of non-nucleated reticulocytes/ erythrocytes changes from < 1.0% on Day 24 to roughly 90% of the total population of circulating RBC in just 17 days, while the percentage of PE drops from 80% to < 10% during the same time period (Table 5). These results suggest the onset of production of a factor or factors that induce or promote maturation of the precursor cells during this time period.