Despite the fact that pig fetuses in late gestation have extensive erythropoiesis, low blood pO(2) 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before term, new-born piglets and piglets 2 and 5 weeks old, blood in amounts corresponding to 2% of body weight was withdrawn from the jugular vein.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.
Copyright 2002 Elsevier Science Inc.