Effect of Total Parenteral Nutrition on Amino Acid and Glucose Transport by the Human Small Intestine

Abstract

The perioperative use of total parenteral nutrition (TPN) as an adjunct to surgical treatment of severely nutrient-depleted patients is appropriate. Potentially deleterious effects of TPN on the gut have been examined with regard to atrophy and gut mucosal barrier function.¹ The specific alterations in nutrient transport, an energy-dependent luminal mechanism, have not, however, been clearly defined. Active transport of specific amino acids across the brush-border membrane is facilitated by a number of carriers, some of which are sodium dependent. ² The maintenance of a sodium gradient requires energy; it is hypothesized that down-regulation of brush-border membrane transport should result from periods of low availability of luminal nutrients. If specific nutrients are physiologically more important, transport would be maintained.

To study these changes, adult patients who were to undergo intestinal surgery were randomized to immediate operation or a 7-day period of bowel rest with calorie and protein needs met by TPN. At celiotomy, segments of distal ileum were obtained and mucosa scraped for the preparation of brush-border membrane vesicles. The brush-border membrane vesicles were coincubated with labeled amino acids in the presence or absence of sodium. By determining the time course of uptake into vesicles, the maximum velocity as well as the affinity of the specific receptor can be determined. By expressing this data as an Eadie-Hofstee transformation, the number of receptor sites can be extrapolated. Specific nutrients examined included glutamine (GLN), methyl-d-amino isobutyric acid (a system A analog), alanine, arganine, and glucose.

A period of no oral nutrition, even with adequate parenteral nutrition support, caused down-regulation in the number of receptors for alanine, arginine, leucine, and glucose. GLN transport, however, was maintained. In a single patient in whom jejunum was available, nutrient uptake was decreased across the board; however, GLN was the least diminished.