Temporal Response of Immunoreactive Erythropoietin to Acute Hypoxemia in Fetal Sheep

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Abstract
Acute hypoxemia was produced in chronically catheterized sheep fetuses to determine the response time necessary to increase plasma immunoreactive erythropoietin (Ep) concentration. Sodium nitrite (0.2 mM) was infused via a fetal vein to induce fetal hypoxemia. The resultant fetal methemoglobinemia was associated with a predictable, incremental decrease in arterial oxygen content. Twelve nitrite infusions were performed in eight fetal sheep preparations (gestational ages 115-146 days). Mean methemoglobin level increased to 33% of total Hb after 1- 2 h of NaNO2 infusion. These results were compared to those obtained in nine control studies in eight fetuses in which no change was observed for plasma Ep, arterial oxygen content, Pao2, pHa, or whole blood lactate. In the nitrite infused group, however, a significant and progressive increase in mean plasma Ep level over baseline levels was observed during the 4th and 5th h of hypoxemia (pa and whole blood lactate levels achieved in these fetuses were in excess of those observed during the nitrite infusions, this possibility was ruled out since no change in fetal plasma Ep levels occurred. We conclude that during the 4th h of acute fetal hypoxemia a predictable, progressive increase in plasma Ep level is observed. This response of plasma Ep to hypoxemia in late gestation fetal sheep is qualitatively similar to that observed in adult animals, thus demonstrating developmental maturity of the fetus.

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