Regulation of iron absorption. II. Relationship between dosage and iron absorption

of a “mucosal block ’ ‘ into medicine. Studies were carried out in three dogs. When a large dose of iron was followed within I.3 to six hours by a dose of radioactive iron, less radioactivity appeared in the erythrocytes than might have been “expected ” in four of five experiments. The idea that a mucosal block existed was apparently rapidly accepted. It formed the basis for the well known suggestion that the apoferritin-ferritin system regulated the entry of iron to the body through the mu-cosa. Subsequently, however, controlled stud-ies of the absorption of iron from various doses were carried out by other investiga-tors.3-5 Using more acceptable means of measuring iron absorption, it was found that although the percentage of iron absorbed decreased with increasing dosage, the total quantity continued to increase. In reviewing the studies of Smith and Pannacciulli4 we no-ticed that the logarithm of the amount of iron absorbed bore a strikingly linear relationship to the logarithm of the amount of iron given. Because it seemed that this relationship might provide us with some insight into the mech-anism of iron transport across the intestinal mnucosa, the studies reported here were carried out in mic