The influence of age and sex on erythropoietin titers in the plasma and tissue homogenates of hypoxic rats.

Experiments were performed to determine the erythropoietin (Ep) content of homogenates of kidneys and livers of male and female rats of various ages. In all studies, homogenates were adjusted to a concentration of 4 g of tissue per 12 ml of phosphate-buffered-saline, and the stimulus to Ep production consisted of exposure to 0.42 atmosphere for 4 h. The concentration of Ep in kidneys of male rats was about three times that found in those of females and was contained predominantly in the cortical portion of the kidneys. Ep was not detectable in kidneys of rats younger than 3 weeks of age, and reached a maximum concentration after 4 weeks of age. The Ep content of the liver was barely detectable regardless of the age of the rat or its plasma Ep titer; and did not increase significantly by administering angiotensin II or CCl4 (substances which increase extrarenal Ep production).