INTESTINAL-ABSORPTION OF PROLINE AND LEUCINE IN CHRONICALLY CATHETERIZED RATS

Background & Aims: Most studies of intestinal amino acid absorption us e methods in which intestinal function is studied immediately after su rgical manipulation. The unphysiological experimental conditions prese nt in these studies limit the ability to extrapolate their results to normal physiological conditions. The aim of this study was to determin e the rates of proline and leucine absorption under normal physiologic al conditions. Methods: Absorption of proline and leucine was measured in long-term catheterized rats using a method of dual infusion of rad iolabeled isotopes, Results: The maximum transport velocity and appare nt membrane permeability for proline were 16.1 mu mol/min and 0.07 mu mol.min(-1).mmol/L-1. For leucine, the maximum transport velocity and apparent membrane permeability were 14.9 mu mol/min and 0.08 mu mol.mi n(-1).mmol/L-1. Surgical bowel manipulation decreased the maximum tran sport velocities for proline and leucine by >80%. The adverse effects of surgery were present for 24 hours. Conclusions: Under normal physio logical conditions, most proline and leucine is absorbed by active tra nsport. Measurements of amino acid absorption using methods in which t he intestine has been surgically manipulated within the previous 24 ho urs significantly underestimate proline and leucine absorption and do not reflect absorption under normal physiological conditions.