Intralipid-based short-term total parenteral nutrition does not impair small intestinal mucosa-related cellular immune reactivity in the healthy rat

Background: The lipid component of total parenteral nutrition (TPN) has rep ortedly been associated with trophic effects on the intestinal mucosa and s uppressive effects on the immune system. Methods: We have challenged these hypotheses using a 7-day TPN rodent model comparing the effects of isocalor ic, isonitrogenous lipid-based (TPN-lipid, 50% of calories as long-chain tr iacylglycerol) and carbohydrate-based TPN (TPN-CH, 100% of calories as carb ohydrates) on mucosal morphology and immune function. Enterally fed animals were included to establish a baseline for immunologic read-outs. The study was performed in healthy, metabolically stable animals to avoid interferen ce by septic or trauma-related stress factors. Results: Both TPN regimens r esulted in a significantly smaller weight gain (TPN-lipid, 29.8 +/- 4.0 g; TPN-CH, 30.3 +/- 4.4 g) compared with enterally fed reference animals (49.2 +/- 3.2 g; p = .007), with no difference in nitrogen balance between the T PN groups. Mucosal sucrase activity was significantly lower in both TPN gro ups (TPN-lipid, 8.8 +/- 1.0 x 10(-7) katal per gram (kat/g) of protein; CH: 11.9 +/- 1.6 x 10(-7) kat/g of protein) compared with enteral feeding (17. 4 +/- 0.9 x 10(-7) kat/g of protein; ANOVA: p = .0007). Morphometric analys is of the small intestine revealed no differences between the two TPN group s although a significantly depressed villus height in the TPN-lipid group c ould be observed in comparison to enterally fed reference rats (TPN-lipid, 0.47 +/- 0.02; TPN-CH, 0.50 +/- 0.01; enteral, 0.56 +/- 0.02 mm; ANOVA: p = .0298). Light and electron microscopy revealed a normal surface architectu re in all three groups of rats. Cellular immune reactivity was evaluated us ing a novel specific immunization protocol: animals were immunized against OVA 4 weeks before TPN. OVA-induced lymphoproliferative responses and pheno typic data from draining popliteal and mesenteric lymph nodes were evaluate d after the different regimens. Results did not differ among the three grou ps. Conclusions: In healthy rodents, short-term lipid-based and carbohydrat e-based TPN regimens lead to limited mucosal atrophy with preserved surface architecture compared with enteral feeding. However, peripheral and mesent eric cellular immune responsiveness after both TPN regimens remained compar able to enterally fed reference animals. Therefore, mesenteric and systemic cellular immune reactivity does not appear to be impaired by lipid-based o r carbohydrate-based TPN.