Regulation of Erythropoiesis XXII. Erythropoietin Production in the Newborn Animal

Erythropoietin production was examined in the newborn rat. Even though there was significant anemia present during the early neonatal phase of life in the rat, erythropoietin could not be demonstrated in the plasma. Exposure to simulated levels of altitude of 23,000 feet for a period of 18 hr. resulted in the production of demonstrable levels of erythropoietin in the plasma. The amount of erythropoietic activity which could be demonstrated in the plasma of hypoxic animals increased with age from values of 0.76 units/ml. in the 1 day old animal to normal adult values of approximately 8 units/ml. by the thirtieth day of life. Bilateral nephrectomy prior to exposure to hypoxia in the 5 day old and 15 day old rat reduced the amount of erythropoietin to values of 50 per cent and 25 per cent of those observed in the intact hypoxic animal. By the thirtieth day of life, erythropoietin could no longer be demonstrated in anephric animals exposed to hypoxia.

It is concluded that there is a gradual increase in the capacity of the rat to produce erythropoietin in response to an hypoxic stimulus, and that in significant measure during the early neonatal phase, erythropoietin production is accomplished by extrarenal sources.