Proteolytic activity as a regulator of the transmission of orally fed proteins from the gut to the blood serum in the suckling rat.

14-day-old rats were orally fed with porcine colostrum or serum having a low or high activity of protease inhibitors (i.e., sow colostrum trypsin-chymotrypsin inhibitor or soybean trypsin inhibitor). The uptake of undigested porcine albumin and IgG to the blood serum of these rats was studied 4 h after feeding. The effect of the exclusion of proteases to the intestinal lumen by means of pancreatic duct ligation prior to feeding was also studied. The results from these feeding experiments in the presence of protease inhibitors or in the absence of pancreatic proteases agreed well. It was concluded that for the sucking rat the intraluminal proteolytic activity in the gastrointestinal tract is a regulator for nonselective protein uptake, as represented by albumin, while the selective absorption of IgG was unaffected.