Mechanism of sex difference in rat tissue iron stores

Abstract

1. 1. The livers, kidneys, and hearts of mature male and female rats were analyzed for total iron, heme iron, and ferritin iron. The females showed a 4–5-fold larger concentration of non-heme iron and ferritin iron in the liver, and a 3-fold larger concentration in the kidney, but no sex difference in the heart. Injection with 25 mg iron as iron dextran 1 week before killing caused extensive deposition of non-heme iron and ferritin in the liver and obliterated the sex difference. In the kidney, iron deposition was less and the sex difference persisted. 2. 2. The rate of liver ferritin protein synthesis was different in the two sexes, the synthesis of ferritin protein per g liver being about 50% greater in female rats. Iron injection 5 h before death stimulated considerable synthesis of ferritin protein in both sexes and the rate of ferritin protein production per g liver became the same. 3. 3. Ferritin breakdown showed a slightly but not significantly more rapid fractional rate in the livers of females. The larger amount of ferritin in the female liver can thus be attributed to more rapid synthesis, presumably due to greater availability of iron, without a change in fractional degradation rate. There is no evidence to suggest that the livers of male and female rats have an inherently different capacity to make ferritin protein, since synthesis and accumulation of ferritin in the liver becomes the same during iron overload.