The need for accurate measurements of amino acid and nutrient absorption under normal physiologic conditions is necessary for determining the mechanisms of intestinal adaptation and the role of modulators of intestinal absorption. Previous measurements of amino acid (AA) absorption have used methods in which intestinal function is studied immediately after surgical bowel manipulation either in vitro or in vivo. These studies show that the maximum transport rates (Jmax) for AAs range from 0.1 to 0.5 μmoles/cm/min and that passive transport exceeds active transport at luminal concentrations as low as 20 and 60 mM. We hypothesize that surgical bowel manipulation significantly decreases AA transport limiting the ability to extrapolate the results of previous studies to normal physiologic conditions. The effect of surgical bowel manipulation was determined by measuring the absorption rates of proline (Pro) and leucine (Leu) in chronically catheterized rats using a dual infusion method (J Clin Invest, 95: 1995). Pro and Leu absorption were measured at concentrations of 100 mM immediately after surgery (0 hr) and then 4 hr, 1 d, 2 d, 3 d and 4 d postoperative (n=6).Table

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Values are mean ± SD in μmoles/min (*p<0.05 vs 4d). Surgical bowel manipulation decreased Pro and Leu absorption by 70%. The adverse effects of surgery were present for at least 24 hrs. Immediately after surgery, the Jmaxs for Pro and Leu transport were 0.2 and 0.1 μmoles/cm/min which are similar to the estimates in previous studies. The characteristics of Pro and Leu absorption without the influence of surgery were determined by measuring the rates of Pro and Leu absorption at least 4 d postoperative at luminal concentrations from 10 - 200 mM. The Jmaxs for Pro and Leu transport were 1.0 and 0.9 μmoles/cm/min, respectively. Active transport accounted for greater than 50% of Pro and Leu absorption even at luminal concentrations of 200 and 150 mM, respectively. We conclude that surgical bowel manipulation significantly decreases intestinal AA transport for at least 24 hrs. Studies of intestinal AA absorption performed within 24 hours of surgical bowel manipulation do not accurately assess intestinal absorptive function under normal physiologic conditions.