Intestinal protein and LPH synthesis in parenterally fed piglets receivingpartial enteral nutrition and enteral insulinlike growth factor 1

Background: Providing partial enteral nutrition (PEN) supplemented with ins ulinlike growth factor-1 (IGF-1) to parenterally fed piglets increases lact ase-phlorizin hydrolase (LPH) activity, but not LPH mRNA. The current aim w as to investigate potential mechanisms by which IGF-1 up-regulates LPH acti vity. Methods: Newborn piglets (n = 15) received 100% parenteral nutrition (TPN), 80% parenteral nutrition + 20% parenteral nutrition (PEN), or PEN + IGF-1 (1.0 mg . kg(-1) . d(-1)) for 7 days. On day 7, [H-2(3)]-leucine was intrav enously administered to measure mucosal protein and brush border LPH (BB LP H) synthesis. Results: Weight gain, nutrient intake, and jejunal weight and length were s imilar among the treatment groups. Partial enteral nutrition alone increase d mucosal weight, villus width and cross-sectional area, LPH activity, mRNA expression, and high mannose LPH precursor (proLPH(h)) abundance compared with TPN (P<0.05). Insulinlike growth factor-1 further increased mucosal we ight, LPH activity, and LPH activity per unit BB LPH approximately twofold over PEN alone (P < 0.05) but did not affect LPH mRNA or the abundance of p roLPH(h) (one of the LPH isoforms) or mature LPH. Isotopic enrichment of [H -2(3)]-leucine in plasma, mucosal protein, and LPH precursors, and the frac tional and absolute synthesis rates of mucosal protein and LPH were similar among the treatment groups. Insulinlike growth factor-1 treatment increase d total mucosal protein synthesis (60%, P < 0.05) but not LPH synthesis com pared with the other two groups. Conclusions: Because IGF-1 did not affect the fractional synthesis rate of either mucosal protein or LPH, the authors suggest that enteral IGF-1 incre ases mucosal protein mass and LPH activity by suppressing mucosal proteolyt ic degradation.