Sequential Mechanisms in the Enhanced Absorption of Vitamin B12 by Intrinsic Factor in the Rat*

Pernicious anemia, a clinical state of vitamin B12 deficiency, is characterized by a virtually complete absence of gastric intrinsic factor secretion, result- ing in marked inability of the patient to absorb the low concentrations of vitamin B12 present in usual dietary sources. Intrinsic factor deficiency is also produced by total gastrectomy in the rat and, as in the patient, can be temporarily abolished by the oral administration of intrinsic factor. A number of facts concerning the nature and function of in- trinsic factor have been discovered by observations on patients (1-2) and, recently, on gastrectomized rats (3-5).