Factors affecting the intestinal absocption of orally-given proteins in rats

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Orally given proteins are usually absorbed into body after once they are digested to amino acide or small peptides by proteolytic enzymes in the intestinal tract. However, our observation that Serratia protease (SP,MW 50,600) administered orally to scalded rats dramatically repressed the enhancement of fibrinolysis and blood vessel permeability both induced by the scalding strongly suggested its intestinal absorption. The present investigation was undertaken to make clear whether it is absorbed or not, and to identify any physiological nutritional factors that may control the degree of its intestinal absorption.We first established a highly-sensitive EIA and a protease assay for determining SP concentration in rat plasma. The SP concentration obtained by these two assay on respective plasma samples from SP-administered rats coincided well. This led us to the conclusion that a portion of orally-administered SP was absorbed from the intestinal tract and transferred to the blood stream in … More an enzymatically active form.We then investigated the effect of age and feeding on the intestinal absorption. Four groups of rats of different age were used : 3 weeks-old (suckling), 5 weeds-old (weanling), 11 weeks-old (adult) and 75 weeks-old (aged) rats. They were fasted or provided ad libitum with a chew diet before and after SP administration. The maximum plasma concentraion was realized 1-2 hours after administration. Compared to the adult groups (3 ng/ml) other three groups all gave a higher plasma concentration. In the suckling group it reached to as high as 130 ng/ml. Feeding also remarkably affected the absorption. In the fed aged group the highest concentration was elevated to 160 ng/ml, a 10-fold increase against that of fasted aged group. These results suggest the presence of some characteristic structures and functions in the intestinal tracts of suckling rats and aged rats that enables the enhanced absorption of proteins. This enhancement might be useful as an indication of ageing. Less