RATE OF [N-15]LEUCINE INCORPORATION AND DETERMINATION OF NITROGENOUS FRACTIONS FROM GASTRO-JEJUNAL SECRETION IN FASTING HUMANS

The aim of this study was to quantify the nitrogen fraction flow rates in gastro-jejunal secretions in fasting humans and to determine the [N-15] leucine incorporation into the secreted proteins. A double lumen intestinal perfusion method was used in 5 healthy volunteers. Plasma and gastro-jejunal juices were collected during a 15-h intravenous [N-15] leucine infusion. Total, soluble and insoluble nitrogen, amino acids and [N-15] leucine enrichment were measured. The total nitrogen flow rate was 7.2 +/- 1.9 mmol.h(-1) and 58% was ethanol soluble. The amino-acid composition remained constant and glycine was the most abundant. The plasma [N-15] leucine enrichment at the isotopic plateau was 4.8 +/- 0.9 mol% excess. The [N-15] leucine enrichment in the intestinal chyme increased asymptotically to reach a plateau after 5 h. The [N-15] leucine enrichment at the plateau and the fractional synthesis rate of secreted proteins were 1.6 +/- 0.5 mol% excess and 21.5 +/- 3.3%.h(-1), respectively. These results show that the composition of the basal gastro-jejunal secretion is very stable. A part of this secretion is composed of proteins with rapid synthesis rates.