ABSORPTION AND SECRETION OF EXOGENOUS AND ENDOGENOUS N ALONG THE DIGESTIVE-TRACT AND KINETIC-PARAMETERS OF PROTEIN-METABOLISM IN GROWING PIGS .1. ESTIMATION BY DIGESTA EXCHANGE BETWEEN N-15-LABELED AND UNLABELED PIGS

Three female pigs of about 30 kg body weight were fitted with re-entra nt cannulas into the duodenum and ileum, and with catheters into the b ladder. One pig was labelled with N-15 by 5 days continuous infusion o f [N-15]leucine (36.2 atom percentage N-15) into the vena jugularis. R ates of N absorption, secretion and re-absorption were estimated using the method of digesta exchange between previously N-15-labelled and u nlabelled pigs during the next 3 days and calculated according to the isotope dilution method. Between the mouth and the upper duodenum, 14. 3% of N ingested was absorbed and 9.3 g N/day was secreted. In the sma ll intestine, 70.5% of N ingested was absorbed and 9.7 g N/day secrete d, which accounted for 41.3% N secreted into entire tract. In the larg e intestine, 7.4% of dietary N was absorbed and 4.5 g N/day was secret ed. The total amount of N secreted into the entire digestive tract was 23.5 g/day, which accounted for 67.3% of N ingested. Of the secreted endogenous N, 21.3 g N/day was re-absorbed.