IN VITRO ASSAY FOR HUMAN INTRINSIC FACTOR*

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Abstract
Homogenate of mucosa from the distal half of the guinea pig small intestine appears to provide a simple, reliable, rapid in vitro assay for intrinsic factor, which correlates well with in vivo assays. The present study demonstrates this with both human and hog intrinsic factor. The specificity of the system for intrinsic factor is further suggested by the findings that the activity of gastric juice in the homogenate system, like the activity of intrinsic factor, is reversibly inhibited at pH 5.8 and below, and is destroyed by heat or prolonged exposure to acid, but not by moderately alkaline pH or by storage at -20[degree]C at neutral pH. Antibody to human stomach mucosa inhibits the uptake of B12 mediated by human gastric juice. B12-binding proteins other than intrinsic factor do not enhance B12 uptake by the homogenate. The homogenate may be stored frozen or lyo-philized and stored at room temperature for use as needed. The assay may be incorporated into routine gastric analysis, requires less than 1.0 ml of gastric juice, is a direct measure of intrinsic factor activity, and can provide results within an hour.