Changes in the kidney and blood following hypoxic hypoxia in rats.

1. Rats were rendered hypoxic by maintaining them within silicone rubber membrane covered enclosures. In experiment one the inspired oxygen concentration was progressively reduced from 21 per cent to 7 per cent over a period of 13 days. In the second experiment the inspired oxygen was maintained at nine per cent for seven days. 2. The reticulocyte counts, haematocrit values and haemoglobin concentration of blood samples from control and hypoxic rats were measured. These results showed a significant increase in all three parameters in both experiments compared with the values from control rats. 3. The renin content of the kidneys of the rats was bioassayed by its hypertensive effect in bilaterally nephrectomised rats. There was no significant difference in renal renin content of the hypoxic rats of experiment one or two when compared with their controls. These results do not support the concept that the juxtaglomerular cell granule is a source of erythropoietin or its precursors in rats.