Effect of starvation on amino acid and peptide transport and peptide hydrolysis in humans

Jejunal disappearance rates of glycine (a model for neutral amino acid absorption), triglycine (a model for peptide transport), and tetraglycine (a model for brush-border membrane hydrolysis) were investigated by an in situ perfusion technique before and after 2 wk of starvation in seven obese volunteers. The three test solutions of glycine, triglycine, and tetraglycine were equivalent in glycine content. Before starvation glycine absorption was greatest from the triglycine solution and smallest from the glycine solution. Starvation significantly decreased glycine absorption from both glycine and triglycine solutions, but not from the tetraglycine solution. However, glycine absorption was still significantly greater from the triglycine and tetraglycine solutions than from the glycine solution. Starvation had no significant effect on the disappearance rate of triglycine, but it increased the disappearance rate of tetraglycine. We conclude that a) starvation has different effects on functions of mucosal brush-border membrane, for example, it reduces amino acid absorption but enhances peptide hydrolysis; and b) the greater amino acid absorption from peptides is maintained even after 2 wk of starvation, suggesting that peptides are superior to free amino acids as the nitrogen source for enteral nutrition if employed in malnutrition.