EPO was detected in the plasma of fetal swine on Day 30 and Day 40 (Table 3). The relative decline in EPO between these ages may indicate a physiological difference in fetal erythropoiesis, perhaps due to the rapid expansion of the erythron (circulating RBC plus erythropoietic tissue ) between Day 30 and Day 40. The physiological significance of higher relative plasma EPO values in WC than in MS fetuses on Day 30 and Day 40 is not yet clear but is coincident with lower hematocrits on Day 40 in MS. Not only is EPO involved in production of RBC, but it also plays a role as a mitogen for murine fetal liver stromal cells in vitro and thus may play a role in the growth of the liver at this time in the fetal pig. buy ortho tri-cyclen online
It is thought that EPO is produced by both the liver and the kidney in the adult animal, with the kidney producing the most significant amounts. The liver is thought to produce the majority of circulating EPO in the fetus. However, EPO was not detected by RIA in cytosol preparations of fetal liver or immunohistochemically in fetuses in this study (data not shown). Thus, the source of circulating EPO in the swine fetus is unknown at this time. A previous study also could not detect EPO in liver extracts, despite EPO mRNA localization in the liver, indicating that EPO may be immediately secreted upon production and thus be below detectable levels.