Role of gastric digestion in the absorption of slowly digestible peptide, oligo-L-methionine, in rats.

Absorption of a slowly digestible peptide, oligo-L-methionine (OM), added to a low casein diet was faster than absorption of OM added to a low soybean protein isolate diet in early stages of feeding in chronic portal-cannulated rats. In the present study, the gastric digestion of 14C-labeled OM in rats fed a casein-based diet was higher than that in rats fed an soybean protein isolate-based diet 30 min and 3 hr after feeding. In rats with chronic bile-pancreatic juice diversion from the proximal small intestine, the higher gastric solubilization of OM in the stomach of the casein group was also observed, but the contents of soluble digest of OM in the stomach were lower than those in the normal rats. The portal absorption of OM in the casein group was higher than in the soybean protein isolate group both 30 min and 4 hr after feeding in the bile-pancreatic juice-diverted rats, and the difference of the portal absorption between the diet groups corresponded to the difference of the amount of solubilized OM in the upper small intestine; this, in turn, depends on pepsin digestion in the stomach. These findings suggest that the difference between the two diet groups in the ability to digest OM in the stomach can at least partly explain the higher portal absorption of OM in the casein group in the early stages of feeding.