EFFECTS OF NUTRIENT SOLUTIONS ON CONCENTRATION ANALYSIS OF NONABSORBABLE DILUTION MARKERS - IMPLICATIONS FOR STUDIES OF GASTRIC-EMPTYING

Gastrointestinal luminal contents may interfere with concentration ana lysis of non-absorbable dyes. However, non-absorbable markers are broa dly used for studies of gastric emptying rates of nutrient solutions. This prompted us to evaluate the properties of non-absorbable markers to mark such nutrient solutions. In vitro concentrations of polyethyle ne glycol, phenol red, dextran blue, two anthroquinone dyes and inulin were determined spectrophotometrically in the presence or absence of a formula diet, single com pounds of the diet or an oligo-peptide diet , and the reproducibility and validity of the analyses were evaluated. The presence of the formula diet or the oligopeptide diet seriously i mpaired the analyses of marker concentrations, whereas single nutrient compounds did not uniformly interfere. The analysis of polyethylene g lycol and phenol red concentrations was impaired by proteins, while th e analysis of inulin concentration was impaired by carbohydrates. Dext ran blue and the anthroquinones were completely eliminated by protein- precipitation procedures. In conclusion, phenol red and polyethylene g lycol should only be used as marker substances for protein-free meals or nutrient solutions, while inulin should not be used with meals or n utrient solutions containing carbohydrates. Marker dilution techniques cannot be recommended for measurements of gastric emptying rates of c omplete meals.