Another test compares the intestinal permeability to the monosaccharide L-rhamnose and the dissaccharide lactulose by simultaneously measuring their urinary excretion after oral ingestion of a solution containing both sugars.4 The normal intestine is much less permeable to lactulose than to Lrhamnose, so that the lactulose:L-rhamnose excretion ratio (with both quantities expressed as a percentage of the oral dose ingested) is approximately 0-05.4 In children the upper limit of normal is considered to be 0-07.5 By studying alterations in the absorption of one substance relative to another, errors due to altered gastrointestinal motility, distribution after absorption, and renal excretion should be minimised.4 In this study the lactulose-L-rhamnose test was performed in six patients with cystic fibrosis. Patients and methodsSix patients (four boys and two girls) with a mean age of 12 years (range 8-15 years) participated in the study. All had the typical history of cystic fibrosis and raised concentrations of sweat electrolytes at the time of diagnosis. All patients were taking pancreatic enzyme substitutes.After an overnight fast each patient ingested an oral load (80 ml) containing lactulose (5-3 g in 7-5 ml of 'Duphalac' syrup) and rhamnose (0-75 g). All urine passed over the next five hours was collected, its volume recorded, and a sample, preserved with merthiolate, frozen and stored for analysis.Urine samples were analysed for lactulose and L-rhamnose by quantitative thin layer chromatography with five upward developments on silica gel layers (Schleicher and Schull F1500), with methanol! butanol 1-ol/water, 30/30/30, vol/vol as the solvent for the first two developments, butanol 1-ol/ethanolV acetic acid/water, 60/30/10/10, vol/vol as the solvent for the third and fifth developments, and butanol 1-ol/ethyl acetate/pyridine/acetic acid/water, 5/70/ 15/10/10, vol/vol as the solvent for the fourth development, using raffinose and fucose as internal standards. The sugars were measured by dipping in 1*4% wt/vol 4 aminobenzoic acid in 3-5% vol/vol orthophosphoric acid in methanol and heating for 10 minutes at 120-130'C, measuring the resulting colour by densitometry. Each patient's height (m) and weight (kg) was measured and body mass index (height/weight2) calculated. Forced vital capacity, forced expiratory volume in one second, and the ratio between these measurements was also measured in each patient. For the purpose of comparison, forced vital capacity was calculated as a percentage of that expected for patient's height.6Standard statistical methods were used in attempting to correlate the lactulose:L-rhamnose excretion ratios with the clinical variables. ResultsThe six subjects excreted 13-111 mg (median value 26-8 mg) lactulose and 19-89 mg (median value 26-5 mg) L-rhamnose in the five hours. The lactulose:L-rhamnose ratio was derived from the five hour sugar excretions expressed as a percentage of the oral dose. In these subjects excretion ratios were on 7 May 2018 by guest. Protected by copyright.
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