Studies on the secretion of amino acids and of urea into the gastro intestinal tract of pigs. 1. Secretion of leucine into the stomach and upper part of the duodenum during continuous intravenous infusion of 14C-leucine.

Three pigs of 34 kg live weight were fitted with a re-entrant cannula in the duodenum, and with two catheters placed in the jugular vein and carotid artery. They were fed 1.2 kg/d of wheat-dried-skimmed milk diet. Digesta from the proximal duodenal cannula were collected for 12 h on 2 consecutive days; 50% were reintroduced into the respective distal cannula and 50% were stored at -20 degrees C. Three days later 14C-leucine was infused into the jugular vein for 12 h, starting with the morning meal. During this period the digesta from the proximal cannula were collected and stored for analysis while the digesta collected previously were reintroduced into the distal cannula. Blood samples were taken from the carotid artery. The total flow of duodenal digesta in 12 h was 5760 +/- 530 g. On average 70 percent of the radioactivity in digesta was associated with the TCA-precipitable fraction. During hours 0-3 and 11-12 of infusion 60-70% and 96-98% of the radioactivity in the TCA precipitable fractions was in leucine. In the TCA soluble fraction only 30-40 per cent of the radioactivity was associated with leucine. At the plateau 2.1 and 3.3% of infused 14C-leucine and of radioactivity were recovered in the duodenal digesta. The calculated amount of endogenous protein passing the duodenum was 20.4 g/d/pig. The results are discussed in relation to previous studies on protein synthesis and secretion in which 14C- and 15N-amino acids were used.