Impermeability of the ovine placenta to 35S-recombinant erythropoietin

Controversy exists regarding the placental permeability of erythropoietin (Ep), a glycoprotein hormone that regulates red blood cell production in the fetus, newborn, and adult after tissue hypoxia. The purpose of the current study was to determine the placental permeability of biologically active 35S-labeled human recombinant erythropoietin given by bolus injection into the circulation of the fetal lamb. Specific radioactivity in fetal plasma trichloroacetic acid protein precipitate fractions increased 13-fold from preinfusion levels at 6 h (47 +/- 1.3 to 679 +/- 237 cpm/mL) and thereafter fell progressively until the study was terminated at 45 h. In contrast, maternal trichloroacetic acid protein precipitate fractions demonstrated no detectable increase in radioactivity at any time. Based on the counting precision, a rise in maternal plasma radioactivity of more than 3 cpm/mL would have been detected (i.e. 0.5% of the 582 cpm/mL rise in the fetal protein precipitate counts at six h). Similar data were obtained with simultaneously administered unlabeled human urinary Ep. We conclude that physiologically significant amounts of Ep do not cross from fetus to mother; hence, maternal Ep level functions as a separate indicator of the adequacy of tissue oxygenation in the maternal compartment.