Responses of plasma Epo and kidney and liver Epo mRNA to hemorrhage in perinatal pigs

Despite the fact that pig fetuses in late gestation have extensive erythropoiesis, low blood pO₂ and low hemoglobin concentrations, piglets are born without detectable concentrations of plasma erythropoietin (Epo). In the present study, we have examined the hypothesis that long-term hypoxic stimuli are less efficient than short-term stimuli in stimulating Epo production in perinatal pigs. From fetuses collected by hysterectomy 5 days before term, new-born piglets and piglets 2 and 5 weeks old, blood in amounts corresponding to 2% of body weight was withdrawn from the jugular vein. Twenty-four hours later the animals were killed and their kidney and liver Epo mRNA analysed by a competitive RT-PCR assay. Plasma Epo concentration was estimated by a solid-phase, two-site sequential chemiluminescent enzyme immunometric assay. We found that in nearly fully developed fetuses and in new-born piglets, the concentration of Epo mRNA did not increase upon bleeding. This is in contrast to earlier findings in sheep. In 2- and 5-week-old piglets, bleeding was associated with a 12–15-fold increase in kidney Epo mRNA. In the 2- and 5-week-old piglets, bleeding evoked increased translation of Epo mRNA into the protein hormone. Also in new-born piglets, increased plasma levels of Epo accompanied bleeding, whereas significant changes in gene Epo expression were not observed.