The role of mucosal iron binding proteins in adaptation of iron absorption during protein deficiency and rehabilitation.

1. A state of protein deficiency has been produced in rats by feeding a low protein diet, thereafter a period of rehabilitation with a normal protein but a low iron supply followed. 2. For characterization of the iron metabolism during both periods haemoglobin, total iron binding capacity, liver non-haemin iron, intestinal iron absorption and the uptake of 59Fe in the liver was determined. 3. Under these conditions the amount of 59Fe incorporated into the mucosal transferrin and the ferritin fractions has been measured. Both fractions were obtained from the supernatant of a mucosal homogenate after chromatography on sepharose 6B. 4. In anemia due to protein deficiency the typical increase of 59Fe incorporation into the fraction of mucosal transferrin--usually occuring in iron deficiency--could not be observed. This coincides with the absence of an increased iron absorption. Moreover a decrease of iron absorption is observed, which is associated with a decreased 59Fe ratio of transferrin/ferritin-fraction. 5. After normalization of the protein supply the ratio of 59Fe incorporated into the mucosal transferrin and ferritin fractions was changed remarkably in favor to transferrin together with a several fold increase of the intestinal iron absorption. 6. The conclusion is drawn that mucosal transferrin and ferritin enable the body not only to adapt the absorption to a higher but also to a lower requirement as it is the case in protein deficiency.