Intestinal vitamin B12 absorption in the dog

Abstract

Summary The secretory, immunological, electrophoretic, chromatographic, and physiological properties of the vitamin B 12 binders in dog gastric juice and dog gastrointestinal mucosal extract were studied to determine whether they resembled intrinsic factor of other species. Total B 12 binding capacity of histamine- and urecholine-stimulated dog fundic gastric juice was much higher than that reported for man. Extracts of fundic gastric mucosa showed B 12 binding capacity far higher than that of dog antrum or intestine, indicating that the fundus is the main site of the B 12 binders secretion in the dog. Paper electrophoresis of dog fundic gastric juice revealed a single B 12 binder whose mobility and isoelectric point differed from that of human intrinsic factor, and which was highly susceptible to peptic digestion. When the B 12 binding materials of fundic gastric juice were separated by sequential chromatography on Sephadex G-25, Amberlite IRC-50, and Sephadex G-100 columns, two B 12 binders were obtained, whose electrophoretic mobilities differed from those of human intrinsic factor. These two binders were also inactive on guinea pig and dog intestinal mucosa homogenate assay for intrinsic factor. The secretion of B 12 binders in dog gastric juice, following histamine and urecholine stimulation, also showed a different pattern from that of intrinsic factor in man. Finally, none of the B 12 binders from dog gastric juice or mucosal extracts cross-reacted with the antibody to human intrinsic factor contained in pernicious anemia serum. These results indicate that the B 12 binders of dog gastric juice and dog gastrointestinal mucosa have none of the secretory, immunological, physicochemical, and physiological properties of intrinsic factor in other species but are rather similar to the "tertiary" B 12 binders related to mucosubstances of the gastrointestinal tract.