Total parenteral nutrition [TPN] decreases brush border enzymes in rats and a modest decrease in gln transport in ileal brush border membrane vesicles[BBMV] in humans after TPN. In the present study, we investigated gln and tau uptake from jejunal BBMV. Male Sprague-Dawley rats [150-175g] were randomly assigned to TPN [Trophamine 10%], TPN + rat chow ad libitum or rat chow ad libitum. TPN [glucose, amino acids, electrolytes, choline, vitamins, trace elements] was infused at a rate of 200 mL/kg/d providing 141 kcal and 8.9 g amino acids/kg/d. After 4 days of the respective regimens, 15 cm of jejunum was resected and BBMV prepared by a Mg++ aggregation/differential centrifugation technique and stored at -70°C. Purity of the preparation was verified by measurement of alkaline phosphatase activity. Radiolabeled gln and tau transport were measured in triplicate with two aliquots of BBMV each using a rapid mixing/filtration technique in 240 ug of mucosal protein. Mean weight gain of the rats was: -2.36, 6.25 and 5.28 g/d for the TPN [n=9], TPN + CHOW [6] and CHOW-fed [5] rats, respectively. Mean mucosal weights for the groups were 0.022, 0.049 and 0.04g/cm/rat; mucosal protein in g/cm/rat: 0.08, 0.09 and 0.12 in TPN, TPN+CHOW and CHOW animals. Gln and tau uptakes [pmoles/mg protein/mg mucosa] are summarized in the Table [Mean ± SEM;*p≤0.001 vs TPN + CHOW and CHOW]. These data indicate that short-term TPN, while decreasing mucosal weight, preserves protein/g tissue, significantly increases tau and gln uptake suggesting upregulation of transport activity. Since there was no gln and a small amount of tau [0.25g/L] in TPN, the data suggest that presence of luminal food, as in the chow-supplemented TPN group, reverses the increased uptakes observed in the TPN rats.
Trophamine was a generous gift from McGaw, Inc.
