PARENTERAL-NUTRITION SELECTIVELY DECREASES PROTEIN-SYNTHESIS IN THE SMALL-INTESTINE

We investigated the effects of an elemental diet fed parenterally or e nterally on total mucosal protein and lactase phlorizin hydrolase (LPH ) synthesis. Catheters were placed in the stomach, jugular vein, and c arotid artery of 12 3-day-old pigs. Half of the animals were given an elemental regimen enterally and the other half parenterally. Six days later, animals were infused intravenously with [H-2(3)]leucine for 6 h and killed, and the midjejunum of each animal was collected for analy sis. The weight of the midjejunum was 8 +/- 1.5 and 17 +/- 1.6 g in pa renterally fed and enterally fed piglets, respectively. LPH activities (mu mol.min(-1).g protein(-1)) were significantly higher in parentera lly vs. enterally fed piglets. Total small intestinal LPH activities w ere lower in parenterally vs. enterally fed animals. The abundance of LPH mRNA relative to elongation factor-1 alpha mRNA was not different between groups. The fractional synthesis rate of total mucosal protein and LPH was significantly lower in parenterally fed animals (67 +/- 7 and 66 +/- 7%/day, respectively) than in enterally fed animals (96 +/ - 7 and 90 +/- 6%/day, respectively). The absolute synthesis rate (the amount of protein synthesized per gram of mucosa) of total mucosal pr otein was significantly lower in parenterally fed than in enterally fe d piglets. However, the absolute synthesis rate of LPH was unaffected by the route of nutrient administration. These results suggest that th e small intestine partially compensates for the effects of parenteral feeding by maintaining the absolute synthesis rate of LPH at the same levels as in enterally fed animals.