The relationship between plasma iron and plasma iron turnover in the rat.

Plasma iron turnover has been evaluated in the growing rat. Consistent data were obtained with the intravenous injection of radioiron in the form of ferrous sulfate or ferric citrate. Plasma iron turnover changed as a function of plasma iron concentration. Only part of this effect in the rat was due to the different rates of clearance of mono-and differic transferrin, the latter having a higher iron delivery rate in vivo. An additional effect was shown to relate to the rate of red cell production. With decreased production, the effect of plasma iron on plasma iron turnover was reduced, whereas with increased erythropoiesis there was an additional increment in plasma iron turnover for any increase in plasma iron. Since this effect was observed when increased iron demands were due to an increase in erythroid precursors in the marrow but not in the circulating blood, it is attributed to limitations in iron flow to the marrow. This suggests that erythroid marrow activity and the adequacy of iron supply when studied by ferrokinetic techniques can best be defined by the response curve relating plasma iron concentration to plasma iron turnover.