Intestinal absorption of sucrose in man: interrelation of hydrolysis and monosaccharide product absorption. G M Gray, F J Ingelfinger J Clin Invest. 1966;45(3):388-398. https://doi.org/10.1172/JCI105354. Research Article Find the latest version: https://jci.me/105354/pdf Journal of Clinical Inxestigation Vol. 45, No. 3, 1966 Intestinal Absorption of Sucrose in Man: Interrelation of Hydrolysis and Monosaccharide Product Absorption * GARY M. GRAY t AND FRANZ J. INGELFINGER (From the Evans Memorial Department of Clinical Research, University Hospital, and the Department of Medicine, Boston University School of Medicine, Boston University Medical Center, Boston, Mass.) Disaccharides are hydrolyzed by their specific amounts of the hydrolysis products accumulate enzymes present in the intestinal mucosa (1-3). intraluminally during the process of sucrose ab- Although some current textbooks still state that sorption in man and that these monosaccharides these enzymes are secreted into the intestinal lu- appear to move back from their mucosal site of hy- men (4-7), the concentrations of monosaccharide drolysis to the lumen (13). products free in intestinal contents during disac- The present work is concerned with the rela- charide absorption in vitro (8-10) have been found tion of hydrolysis of sucrose to the absorption of insufficient to support the concept of intraluminal its monosaccharide components, glucose, an ac- hydrolysis. In addition, the low disaccharidase tively absorbed monosaccharide (14, 15, 17), and activity of intestinal contents during the absorp- fructose, which is passively absorbed (14, 15). tion process in vivo (11-13) strongly suggests that the disaccharide either enters the cell before Methods being hydrolyzed or else is hydrolyzed at the cell Thirty-two normal young subjects were studied on 105 surface by mucosa-bound enzyme. The released occasions by use of a double-lumen tube placed at various monosaccharide products presumedly are then levels of the intestine (13, 18). Polyethlene glycol 4000 transported across the intestinal cell (8, 14, 15). (PEG) was used as the nonabsorbable water-soluble Little information is available that relates disac- marker and was determined by a modification of Hyd&i's method (19). Sucrose solution or an equivalent mix- charide hydrolysis to absorption of the component ture of glucose and fructose made isotonic with NaCl monosaccharides. Wilson and Vincent (14) com- (290 ± 10 mOsm per L) was infused at 15 ml per minute mented on the accumulation of monosaccharides in through the proximal orifice of the tube. In some stud- the mucosal medium during the process of disac- ies, galactose was also infused. Intestinal samples were charide absorption in hamster gut sac preparations, collected by siphonage from the distal orifice, which was located 15 or 30 cm from the site of infusion. The ini- and Dahlqvist and Thomson have reported that tial 30 minutes of an infusion period allowed steady state large amounts of free fructose accumulate intra- conditions to be approached so that, thereafter, concen- luminally during sucrose absorption in the intact tration of PEG and the test sugar or sugars in succes- rat (16). Despite these findings in animals, sively collected samples showed little variation (13). Dahlqvist and Borgstr6m found little free intra- When successive experiments were performed in the same intestinal segment, the equilibration period also luminal monosaccharides during the process of served to prevent the contamination of one test by the disaccharide absorption in man (12). It was re- residuals of a preceding test. Absorption rates deter- cently demonstrated, however, that appreciable mined by infusing a specific solution changed little (mean ± 10%) when experiments were repeated during the *Submitted for publication June 10, 1965; accepted course of a 10-hour period; thus there was no evidence of December 2, 1965. "fatigue" of the intestinal segment under study, and ab- Supported in part by U. S. Public Health Service re- sorption of different carbohydrate solutions could be search grant AM 03560-04 and 05 and by training grant compared. The test solutions were infused in random T1 AM 5025-07 and 08 from the National Institute of order, and specimens obtained from the distal orifice were Arthritis and Metabolic Diseases. collected by use of the precautions previously outlined in Presented in part at the Annual Meeting of the Amer- order to insure stability of the carbohydrates (13). ican Society for Clinical Investigation, Atlantic City, Assay of carbohydrates in intestinal samples. After N. J., May 3, 1964. Ba(OH)a-ZnSO4 deproteinization (20), sucrose,' glu- t Address requests for reprints to Dr. Gary M. Gray, U. S. Army Tropical Research Medical Laboratory, 1 a-D-Glucopyranosyl-P-D-fructofuranoside, analytical APO, New York, N. Y. 09851. grade, Merck Co., Rahway, N. J. 388 INTESTINAL ABSORPTION OF SUCROSE IN MAN 389 cose,2 and total hexose (glucose plus fructose) 3 were Sucrose absorption can also be expressed in terms of determined by the specific enzymatic methods previously the individual monosaccharides: described (13). Glucose was substracted from total Glucose product absorption hexose to determine fructose. = [Si V-S,-V-(Pi/P,)J - [G..V'(Pi/P,)], [3] In some of the samples containing only fructose and glucose, fructose was analyzed by Dische and Devi's and ketohexose method (21); values obtained were within fructose product absorption 3% of those found by use of the enzymatic method. = [S1-V-Se-V-(P1/P.) ]-[F.*V (P1/P.)]. [4] Galactose 4 was assayed by a modification of the galac- tose oxidase assay described by Avigad, Amaral, Asensio, The use of Equations 3 and 4 is necessary if absorption and Horecker (22). The reagent consisted of 125 U of sucrose is to be compared with that of an equivalent galactose oxidase,5 3 mg peroxidase,6 0.6 ml of 1% glucose-fructose mixture. o-dianisidine in 95% ethanol, 100,000 U catalase,5 and 65 ml of 0.5 M Tris buffer (23) at pH 7.0. It was neces- Results sary to prepare the reagent daily since the chromogen rapidly became colored. To 1 ml of deproteinized sample Comparison of absorption of sucrose versus glu- 2.5 ml of the reagent was added. The reaction mixture cose-fructose mixture. To investigate the relation was incubated at 370 C for 20 minutes and the reaction between the hydrolysis of the disaccharide and stopped with 0.1 ml of 1 N H2SOs Extinction was de- transport of its monosaccharides, we undertook termined in a spectrophotometer at 395 m/A and a 1-cm light path used. A linear relationship of optical density paired experiments comparing absorption from su- to concentration occurred when 50 to 125 ,ug of galactose crose (73 mM) with that from an equivalent mix- was in the cuvette. Amounts of galactose less than 50 ture containing glucose plus fructose (73 mM each /Ag produced little absorbance. Sucrose, glucose, and monosaccharide). Experiments at a given intesti- fructose in 25 times the concentration of galactose read nal level were performed over successive 60-minute the same as the reagent blank and did not interfere with the reaction. Recovery of galactose added to intestinal intervals and the solutions infused in random contents was 100 ± 4%. order. A 30-cm distance between infusion orifice Calculations. Sucrose disappearance over the intesti- and collection orifice was used. As shown in Ta- nal segment may be considered as equal to the sucrose ble I, glucose and fructose absorption rates were hydrolyzed, since appreciable amounts of sucrose do not not significantly different whether the disaccharide disappear by absorption into blood of the intact disac- charide; this was discussed in a previous report (13). was infused (mean: glucose, 35 mmoles per hour; Considerable quantities of the monosaccharide hydroly- fructose, 21 mmoles per hour) or the monosac- sis products of sucrose accumulate intraluminally during charide mixture was infused (mean: glucose, 39 the absorption process, and therefore amounts of the mmoles per hour; fructose, 25 mmoles per hour). monosaccharide found at the collecting orifice must be Also, a similar relation prevailed in 13 paired subtracted from the sucrose hydrolyzed (sucrose that disappeared) to determine absorption (13). studies when 29 mM sugars were infused. This is summarized in Table I. Sucrose hydrolysis=2[S1 V-Se-V-(P1/P.)], and [1] sucrose absorption = 2 [S.V -S.eV- (P1/P.) ] Figure 1 relates glucose absorption rates in in- - [(Ge + F) V (P1/Pe)J, [2] dividual paired experiments and demonstrates that where hydrolysis and absorption are expressed as mil- there is close correlation to linearity (r = 0.87, limoles monosaccharide per hour, and symbols refer to p < 0.001) as well as to the theoretical line repre- millimolar concentrations as follows: St = sucrose in in- senting identical absorption from either infusion fusion; S. = sucrose in collected samples; P1 = PEG in solution. A significant correlation, but of some- infusion; P. = PEG in collected samples; G. = glucose what lower order, was also found for fructose ab- in collected samples; F. =fructose in collected samples. V = volume (liters infused in 1 hour). sorption (r = 0.62, p < 0.01) (Figure 2). Effect of galactose on sucrose hydrolysis and 2 D-Glucose, analytical grade, Merck Co., Rahway, N. J. 3.D-Fructose, C. P. Pfanstiehl Co., Waukegan, Ill. absorption. In our experiments the rate of su- 4 D-Galactose, C. P. Pfanstiehl Co., Waukegan, Ill. crose hydrolysis was greatly different in jejunum Although all other carbohydrates used were chromato- and ileum (Table I) (13). Despite this, similar graphically pure (less than 1% impurity), D-galactose amounts of monosaccharide products accumulated contained 5% D-glucose (as measured by glucose oxidase at all levels of intestine (Figure 3), suggesting the and hexokinase reagents) and a trace of an oligosac- charide. possibility that the hydrolytic process was inhibited 6 Worthington Biochemical Corp., Freehold, N.