Detection of high erythropoietin titers in renal extracts of hypoxic rats.

Previous attempts to extract erythropoietin from the kidneys have not been uniformly successful and have yielded only small amounts. Attempts were therefore made to extract erythropoietin from renal extracts prepared from the supernatant obtained after homogenizing kidneys in various liquids and centrifuging at 2300 x g. Detectable amounts of erythropoietin were recovered from kidneys of nonhypoxic male but not female rats. After exposure to hypoxia, the amounts increased to levels greater than 6.0 U/kidney from males after 8 hr of hypoxia. Erythropoietin became detectable in extracts from kidneys obtained from females after 2 hr of hypoxia and rose to levels of 0.54 U/kidney after 4 hr of hypoxia. The amount of plasma trapped in the kidneys at the time of extraction was not sufficient to account for a significant amount of this erythropoietin, and erythropoietin was not detected in extracts made from livers or spleens. Severalfold larger titers of erythropoietin were detected in renal extracts, by a simple extraction procedure, than was the case in previous attempts. The reasons for this difference are discussed.