Bonnet, John D.

Abstract A simple test is proposed for evaluating the gastrointestinal absorption of iron. It begins with an oral dose of 50 µg. of stable iron labeled with 1 µc. of Fe59, to which about 300 mg. of ascorbic acid are added. Feces are assayed for Fe59 until any single stool contains less than 1 per cent of the dose. Absorption is determined on the assumption that all unrecovered Fe59 has been absorbed. The test was designed to minimize handling of stools by assaying whole specimens, and this process has the added virtue of increasing statistical accuracy of the measurement of radioactivity. The main advantage of the procedure using a 50 µg. dose is that with it one obtains a normal value for absorption which is about one-half of the dose. This permits measurement of either increased or decreased iron absorption. With our standard test method, 19 normal women absorbed an average of 62 per cent of the dose and 22 normal men absorbed 40 per cent. In addition to this sex difference, not explained by the difference in their blood hemoglobin levels, there seemed to be a tendency toward reduced absorption with greater age. Preliminary results of this test in patients with hypochromic anemia and steatorrhea are reported. Increased absorption of iron followed the administration of ascorbic acid whether the iron was in the ferric or the ferrous form. The concept that ferrous iron is better absorbed by man requires re-evaluation.

Forty-two male and female mice, 8 weeks old, were given radioiron (Fe59) in doses of 0.006–0.1 µc, containing 0.013–0.17 µg of iron, by intraperitoneal or intravenous routes. Assays of the radioactivity of the whole body revealed an initial rapid loss of Fe59 (15–20%) lasting about 6 days. Thereafter the Fe59 left the mice at a steady rate of 0.39%/day (half-life 180 days). One 34-year-old normal man was given 10.6 µc of Fe59, containing 8.2 µg of iron, intravenously. Based on counts from the entire body, the biologic rate of loss of the Fe59 was about 0.14%/day (half-life 500 days), and there was little or no initial loss such as occurred in the mouse. The Fe59 in the circulating erythrocytes was essentially unchanged for the first 3 months. It then fell to a new level of about 90% of the previous one; the mid-point of the fall was about 120 days after the administration of the radioiron. The difference in the rates of loss of radioiron from mice and man seems to be related primarily to the life span of the circulating red cells.