An assay for gastric intrinsic factor

¹ Department of Physiology, Harvard Medical School, Boston, Massachusetts

The stimulation of vitamin B₁₂ uptake by small segments of hamster ileum in the presence of gastric intrinsic factor (IF) has been utilized as a quantitative assay for rat and hamster IF. About 100–150 small segments of everted ileum of the hamster were mixed in a beaker and aliquots of approximately 10 were incubated in flasks containing radioactive B₁₂ with or without IF. Within a certain range of IF concentrations, B₁₂ uptake into the tissue was proportional to the IF added. Of all the tissues studied only gastric mucosa showed IF activity under these conditions. This assay was not only specific for gastric IF, but was also extremely sensitive, giving a positive reaction with a concentration of 0.1 mg gastric mucosa per milliliter of incubating solution.