American Journal of Clinical Nutrition, Vol 23, 156-164, Copyright © 1970 by The American Society for Clinical Nutrition, Inc.

Study of the Intestinal Absorption of ⁵¹Cr-Labeled Intrinsic Factor

¹ From the Gastroenterology Research Laboratory and Section of Gastroenterology, Department of Medicine, New York Medical College, New York, New York

To evaluate the possibility that intrinsic factor is absorbed from the gastrointestinal tract, intrinsic factor from human and hog sources was partially purified by ion-exchange column chromatography and gel filtration and labeled by incubation with ⁵¹CrCl₃. The labeled product retained the characteristics of intrinsic factor, as measured by electrophoretic behavior, ability to bind B₁₂, stability on acid incubation when bound to B₁₂, and ability to enhance B₁₂ uptake by guinea pig intestine mucosal homogenate. The ⁵¹Cr hog intrinsic factor concentrate retained its activity when tested in patients with pernicious anemia.

The labeled intrinsic factor preparations were administered, bound either to radioactive or nonradioactive B₁₂, to four normal volunteers and seven individuals with deficient or absent intrinsic factor secretion. Study of the absorption of both labels by radioactivity measurements of urine, feces, and plasma, as well as hepatic surface scintillation counting, and, in the case of 3 normal subjects, whole-body counting, demonstrated no significant absorption of the ⁵¹Cr label. There was evidence, however, of absorption of radioactive B₁₂, which further substantiated the intrinsic factor activity of the labeled preparation.

Our data do not support the contention that the intrinsic factor molecule enters the circulation from the intestine in the process of B₁₂ absorption in an intact state. This does not exclude the possibility that unlabeled fragments of intrinsic factor may enter the circulation from the intestine or that intrinsic factor may enter into the circulation from the gastric mucosa as a result of an endocrine-exocrine partition under pathological conditions.