BACKGROUND & AIMS: Most studies of intestinal amino acid absorption use methods in which intestinal function is studied immediately after surgical manipulation. The unphysiological experimental conditions present in these studies limit the ability to extrapolate their results to normal physiological conditions. The aim of this study was to determine the rates of proline and leucine absorption under normal physiological conditions. METHODS: Absorption of proline and leucine was measured in long-term catheterized rats using a method of dual infusion of radiolabeled isotopes. RESULTS: The maximum transport velocity and apparent membrane permeability for proline were 16.1 mumol/ min and 0.07 mumol.min-1.mmol/L-1. For leucine, the maximum transport velocity and apparent membrane permeability were 14.9 mumol/min and 0.08 mumol.min-1.mmol/L-1. Surgical bowel manipulation decreased the maximum transport velocities for proline and leucine by > 80%. The adverse effects of surgery were present for 24 hours. CONCLUSIONS: Under normal physiological conditions, most proline and leucine is absorbed by active transport. Measurements of amino acid absorption using methods in which the intestine has been surgically manipulated within the previous 24 hours significantly underestimate proline and leucine absorption and do not reflect absorption under normal physiological conditions. (Gastroenterology 1997 Sep;113(3):865-74)
