The subcellular localization of the erythrostimulant factors present in the kidney and spleen of the rabbit.

The subcellular localization of erythrostimulant factors contained in the kidney and spleen of the rabbit have been studied. This was done by subjecting homogenates to fractionation by centrifugation and assessing the erythrostimulant capacity of the hypotonic extracts prepared from the various fractions thus obtained. The results of these studies show that the erythrostimulant factors are present in the light mitochondrial and microsomal fractions of the normal kidney. In conditions of anaemia they are to be found not only in the above-mentioned fractions but also in the mitochondrial fraction. By contrast, in the spleen such factors are present only in the mitochondrial fraction. It is likely that the different localization of the erythrostimulant factors in the kidney and in the spleen of the rabbit may be closely connected with the different functions performed by these organs in the humoral regulation of erythropoiesis.