Effects of proteolytic enzymes on vitamin B12 uptake by rat intestinal mucosa homogenates and of proteolytic enzymes and anti-rat intrinsic factor antibodies on vitamin B12 absorption in total gastrectomized rats.

Trypsin inhibited 57CoB12-rat IF uptake by rat small intestinal mucosa homogenates in vitro. This tryptic inhibition was inactivated by rat serum and normal human serum, as well as soybean trypsin inhibitor (STI). The effects of trypsin dissolved in distilled water or 0.0025 N HCl, 0.15 M saline extract of rat pancreas and STI on vitamin B12 absorption were studied in vivo, using gastrectomized rats. IF-mediated B12 absorption was significantly decreased by 5 mg of trypsin dissolved either in distilled water or 0.0025 N HCl. However, the inhibition of trypsin was much more remarkable when it was dissolved in 0.0025 N HCl, whereas B12 absorption was insignificantly decreased by administering 10 mg of trypsin dissolved in 0.0025 N HCl. The possibilities of this phenomenon was discussed. The inhibitory effect of 0.5 ml of 0.15 M saline extract of rat pancreas was investigated as well. Soybean trypsin inhibition showed no effect on B12 absorption when it was given with 57CoB12-rat IF at the same time. However, the B12 absorption was significantly increased when STI was given one hour prior to the administration of 57CoB12-rat IF. This suggested that endogenous trypsin bound to rat small intestine had been inactivated and pancreatic secretion had been stimulated by STI. IF-mediated B12 absorption was diminished to almost the same level of 57CoB12 administration alone by simultaneous intubation of both 57CoB12-rat IF and rabbit anti-rat IF serum in total gastrectomized rats.