Journal of Clinical InvestigationVol. 44, No. 3, 1965

Intestinal Absorption of Sucrose in Man: The Site ofHydrolysis and Absorption *

GARYM. GRAYt AND FRANZ J. INGELFINGER(From the Evans Memorial Department of Clinical Research, Massachusetts Memorial Hos-

pitals, and the Department of Medicine, Boston University School of Medicine,Boston University Medical Center, Boston, Mass.)

Sucrose, unlike the other common disaccharides,maltose and lactose, has been reported to be ab-sorbed poorly from jejunum in man. Using asingle-lumen tube technique and giving a carbo-hydrate-protein-fat meal with a single disaccharideas the source of carbohydrate, Dahlqvist and Borg-str6m (1) reported efficient absorption of lactoseand maltose from human jejunum but minimalabsorption of sucrose. They assumed that sucrosemust have been absorbed in lower jejunum andileum, but no ileal studies were performed. Thisapparent difference in the site of absorption of su-crose as compared to maltose and lactose has beenquoted as fact (2, 3), and, if true, might serve todistinguish jejunal and ileal malabsorptive diseasein man on the basis of comparative blood sugarcurves after ingestion of the different disaccha-rides.

Dahlqvist (4) subsequently reported data dem-onstrating maximal activity in human jejunum forthe sucrose splitting enzyme, sucrase, but he didnot relate this information to the site of hydrolysisand absorption of sucrose. In addition, recent ex-tensive disaccharidase determinations on humanintestinal mucosa by Auricchio and co-workers(5) have demonstrated activity of sucrase in je-junal and ileal mucosa to be similar, a findingthat would not be expected if sucrose were hy-drolyzed and absorbed principally in ileum.

* Submitted for publication August 25, 1964; acceptedNovember 19, 1964.

Supported in part by U. S. Public Health Service re-search grants AM03560-04 and 05 and by training grantsT1 AM 5025-07 and 08 from the National Institute ofArthritis and Metabolic Diseases.

Presented in part at the Annual Meeting of the Gastro-enterological Research Forum, Dallas, Texas, April 23,1964.

t Address requests for reprints to: Captain Gary M.Gray, MC, U. S. Army Tropical Research Medical Lab-oratory, APO, New York 09851 (San Juan, P. R.).

The present studies were designed to examinefurther the absorption of sucrose in normal man.

Methods

Twenty-three normal young adults (21 males, 2 fe-males) were studied on 50 occasions. A double-lumenpolyvinyl tube with a small, terminal, mercury-filledballoon (6) was swallowed the evening before the studyand allowed to move into the small intestine overnight.Subjects were permitted to have a supper containingclear liquids on the day before the study, but they in-gested nothing but water for the 12-hour period beforebegining the experiment. One lumen of the tube wasused to collect intestinal samples through an orifice placedjust proximal to the terminal balloon. The other lumen,through which the test solution was infused, had its open-ing 30 cm proximal to the collecting orifice. Positionof the tube was checked fluoroscopically before the study,and any coiling in the stomach was removed. When thecollecting orifice was a distance of 60 to 100 cm fromthe incisor teeth, it was found fluoroscopically to be inthe duodenum, when 100 to 170 cm in the jejunum, andwhen 170 to 260 cm in the ileum. At distances exceed-ing 260 cm, the distal orifice of the tube was often foundto be in the colon. These relationships are similar tothose previously reported (1, 6-8).

The test solution contained sucrose 1 at a concentrationof 73 mM (2.5% solution) or 146 mM (5%o solution)as well as sufficient sodium chloride to make the osmo-lality 290 ± 10. These concentrations of sucrose wereselected because Dahlqvist and Borgstr6m found disac-charide concentrations to be in this range in human in-testinal contents after an oral meal (1). The solutionwas infused through the proximal lumen at 15 ml perminute by a peristaltic pump,2 and two to four consecu-tive 20-minute samples were collected by siphonage fromthe collecting orifice 30 cm distal to the point of infu-sion. Approximately 20%o of the infused volume wascollected by this technique. Polyethylene glycol 4000(PEG) 0.5%o was added to the infusate as the nonab-

1 a-D-Glucopyranosyl p-D-fructofuranoside, analyticalgrade, Merck Co., Rahway, N. J. All sugars werefound to have less than 0.5%o impurity by paper chro-matography.

2 Model 600-1200, Harvard Apparatus Co., Dover, Mass.

390

INTESTINAL ABSORPTIONOF SUCROSEIN MAN

sorbable, water-soluble marker, and measured by amodification of Hyden's method (9). After an initial30-minute equilibration period, there was little variation inthe concentration of PEG in siphoned samples from onecollection period to the next (mean ± 5%), and thevalues for disappearance of the test sugar were repro-ducible (mean ± 7%). Samples were collected in ves-sels surrounded by crushed ice and either deproteinizedand analyzed immediately or stored at - 150 C. Speci-mens frozen for 2 to 3 months were found to containthe same amounts of sucrose and its monosaccharideproducts as were present immediately after collection,and only minimal variations were noted even after freez-ing for 4 to 12 months. The infusate samples as well asthose siphoned from the distal collecting site were de-proteinized by Ba(OH)2 and ZnSO4 (10) and then filteredthrough no. 42 Whatman paper. The filtrate was ana-lyzed for sucrose, its monosaccharide products, and PEG.

Sucrose determination. Sucrose was analyzed by a two-step reaction: a) hydrolysis of 1 ml of deproteinized fil-trate (containing up to 3 mg of sucrose) by incubationfor 1 hour at 37° C with 1 ml of buffered yeast invertasesolution (1) (20 mg invertase3 in 100 ml of 0.1 M so-dium acetate adjusted to pH 4.5); and b) assay of the glu-cose produced from the hydrolysis reaction by a modifi-cation of Huggett and Nixon's (11) glucose oxidase(G.O.) reagent [25 mg glucose oxidase,4 3 mg horse-radish peroxidase,5 0.5 ml of 1%o o-dianisidine in 95%oethanol, 100 ml 0.5 M Tris buffer (12) or 0.100 M Tris-0.005 Mphosphate buffer (13) at pH 7.0]. Any free glu-cose present in the original sample before the hydrolysisstep was subtracted from total glucose found afterhydrolysis. No filtering of the G.O. reagent was re-quired, and it was stable for several days under refrigera-tion at 100 C.

To 1 ml of the hydrolyzed solution, diluted as neces-sary, 2.5 ml of the G.O. reagent was added; incubationwas carried out for 1 hour at 370 C, and the color in-tensity was read at 420 mu in a spectrophotometer. Su-crose and D-glucose 6 standard solutions, as well as ap-propriate reagent and invertase blanks, were handledidentically to samples. A linear relationship of opticaldensity to concentration prevailed from 0 to 75 Atg of glu-cose in the reaction mixture. Assay of hydrolyzed su-crose solutions for total glucose plus fructose by thehexokinase reagent (described below) showed that equalamounts of glucose and fructose were released when su-crose was hydrolyzed, thereby demonstrating that meas-urement of the glucose hydrolysis product is a validmeans of determining sucrose. Sucrose or glucose orboth added to small intestinal contents individually or incombination to yield 1 to 150 mMconcentrations could berecovered 100± 5% by the method. The Tris in thebuffer completely inhibited activity of contaminating in-

3 Analytical grade, Nutritional Biochemicals Corp..Cleveland, Ohio.

4Purified Type II, Sigma Chemical Co., St. Louis, Mo.5 Nutritional Biochemicals Corp., Cleveland, Ohio.6 Analytical grade, Merck Co., Rahway, N. J.

vertase in the glucose oxidase so that it was possible toaccurately assay 5 ug of glucose even when 2,500 /Ag ofsucrose was present in the reaction mixture. Sensitivityof the method was found to be the same with the Trisbuffered reagent as with the more commonly used phos-phate buffer (11).

Glucose-fructose determiniation. Considerable quanti-ties of glucose and fructose, the monosaccharide hydroly-sis products of sucrose, were found in the collected in-testinal samples. Total glucose plus fructose7 wasspecifically assayed by a modification of Schmidt's (14)hexokinase-phosphohexose isomerase-glucose-6-phosphatedehydrogenase system. The hexokinase reagent con-sisted of 50 ml of .05 M triethanolamine buffer at pH 7.6(15), 2 ml of 100 mMATP,8 2 ml of 100 mMMgCl2,16 enzyme U of glucose-6-phosphate dehydrogenase,9 8enzyme U of hexokinase,9 and 8 enzyme U of phospho-hexose isomerase.9 To 0.5 ml of the deproteinized filtrate,suitably diluted, 2.5 ml hexokinase reagent was added.One-tenth ml (0.4 mg) of TPN was added to start thereaction. The reaction mixture was incubated at 300 C for1 hour, and the amount of TPNH produced was deter-mined spectrophotometrically at 340 m1u. Deproteinizedsamples plus reagent were found to read the same aswater plus reagent; hence it was not necessary to ob-tain a control spectrophotometric reading before addingTPN. However, a blank containing water, reagent, andTPN was used since the TPN itself did result in somespectrophotometric reading. Since deproteinized intesti-nal samples did not contain detectable amounts of inter-mediate reaction products (glucose-6-phosphate, fruc-tose-6-phosphate), it was not necessary to add individualenzymes sequentially; therefore all enzymes were in-cluded in the reagent. Zero to 40 ,ug of total hexose(glucose or fructose or both) in the reaction mixtureresulted in a linear relationship of optical density to con-centration. Optical density readings were stable for atleast 2 hours after incubation, and sucrose in samples didnot interfere with the reaction.

Sucrase assay. All samples collected during the stud-ies were assayed by measuring the glucose released(G.O. method above) from incubation of equal volumesof collected intestinal sample and 0.056 M sucrose sub-strate according to Dahlqvist (1, 4) except for the fol-lowing modifications: a) a buffer pH of 5.8 was usedinstead of 6.0, since Auricchio and co-workers (5) haveshown this to be the pH optimum for human disacchari-dases; b) the control reaction at time zero and theincubated reaction at 1 hour were stopped with Ba (OH)2-ZnSO4 deproteinization (10) rather than by boiling.Deproteinization was found to be as effective as boiling indestroying the sucrase activity present.

Calculations. Sucrose that disappears from the in-testinal lumen might be absorbed intact or be hydrolyzed

7 D-Fructose, Pfanstiehl Co., Waukegan, Ill.8 Sigma Chemical Co., St. Louis, Mo.9 C. F. Boehringer and Sons, Mannheim, Germany (dis-

tributed by California Corporation for Biochemical Re-search, Los Angeles, Calif.)

391

GARYM. GRAYAND FRANZ J. INGELFINGER

to its monosaccharide products, glucose and fructose.However, in man no appreciable amount of sucrose ap-pears to be absorbed intact into the blood, for any su-crose that enters blood is excreted quantitatively in urine(16-19), but only trace amounts are found in urine ofhumans after a sucrose meal (20-23). Further, no su-crosuria was found in our subjects as measured by enzy-matic assay or by paper chromatography (20, 21). Henceit may be assumed that whatever sucrose disappears ishydrolyzed before it enters the blood stream.

Not all of the products of sucrose hydrolysis were ab-sorbed, however, in the test segment, since appreciablequantities of glucose and fructose were found within thelumen at the collecting orifice. Hence sucrose absorp-tion was determined in terms of its monosaccharideproducts as follows: sucrose disappearance = sucrose hy-drolysis=2 [Sr-V-S SV (Pi/Pc)]; sucrose absorp-tion=2[Sr V-S0'V-PI/Pc]-[(Gc +Fc)V (Pi/Pc)].Hydrolysis and absorption are expressed as millimolesmonosaccharide per hour, and symbols refer to millimolarconcentrations as follows: Si= sucrose in infusion; S =

sucrose in collected samples; V = volume (liters infusedin 1 hour); Pi = PEGin infusion; P, = PEGin collectedsamples; Gc=unabsorbed glucose in collected samples;FC = unabsorbed fructose in collected samples.

Results

Site of sucrose hydrolysis and absorption. Fig-ure 1 demonstrates the results of paired infusionstudies carried out in eight subjects who received73 mMsucrose and in eight different subjects whowere given 146 mMsucrose. Except for one sub-ject in each group, absorption of sucrose was morerapid from jejunal than from ileal segments, thedifferences being statistically significant for both73 mMand 146 mMconcentrations (paired analy-sis t test, p < 0.001). Figure 2 represents theresults of 36 studies in 23 subjects given 146 mMsucrose. Included are the paired studies previ-

INFUSION: SUCROSE 146 M MOLAR

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FIG. 1. PAIRED STUDIES OF SUCROSEABSORPTION IN 30-CM INTESTINAL SEGMENTS

AT VARIOUS INTESTINAL LEVELS. Each group of bars represents studies on one sub-ject, and numbers under bars refer to intestinal level of collecting orifice. Sucroseabsorption is expressed in terms of total monosaccharide absorption. Jejunal absorp-tion rates are significantly greater than ileal (p < 0.001).

392

170 204 140 190 150 195 140 230

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INFUSION: SUCROSE73 M MOLAR

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INTESTINAL ABSORPTIONOF SUCROSEIN MAN

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FIG. 2. SUCROSEABSORPTION-FROM 30-cM INTESTINAL SEGMENTS. Absorption is expressedas in Figure 1. Included are the paired infusion studies shown in the upper half of Figure 1as well as all other sucrose 146 mMinfusion studies. Jejunal absorption is significantly greaterthan ileal (p < 0.001).

ously mentioned as well as all other studies with146 mMsucrose. Absorption was maximal in je-junum and considerably less in ileum (p < 0.001).

During the process of absorption of sucrose, itshydrolytic products glucose and fructose accumu-

lated in the lumen in appreciable quantities. Theamounts of total monosaccharide that appeared are

shown in Figures 3 and 4. The glucose and fruc-tose that accumulated intraluminally presumablyrepresented unabsorbed products of sucrose hy-drolysis. That these monosaccharides did notcome from a source other than sucrose is sup-

ported by the finding that intestinal contents of 15fasting subjects, three of whomwere given iv glu-zose to increase the gradient between blood andintestinal lumen, contained no detectable glucoseor fructose.

Figure 3 relates monosaccharide accumulationto the level of intestine under study. Accumula-

tion was slight in duodenum and considerablygreater in jejunum and ileum; however, despitethe greater sucrose absorption rates in jejunum,

there was no difference in the amount of monosac-charide accumulating intraluminally in jejunal as

compared to ileal segments. In addition, even

though the intraluminal monosaccharides are pro-

duced from sucrose, the linear relationship betweenmonosaccharide appearance and sucrose disap-pearance, i.e., sucrose hydrolysis, was of a loworder (r = 0.51) (Figure 4). However, it isquite unlikely that this degree of correlation couldhave occurred by chance (p < 0.001).

Table I summarizes the results of all infusionstudies. Comparison of the mean rates of hydroly-sis and absorption demonstrates that hydrolysisexceeded absorption by a greater relative amountin ileum. This is expressed in the last two col-umns in Table I, where the fraction of hydrolyzed

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GARYM. GRAYAND FRANZ J. INGELFINGER

sucrose that was absorbed is compared with thatwhich accumulated intraluminally. The fractionof hydrolyzed sucrose absorbed was significantlygreater in jejunum than in ileum (p < 0.01).

Intraluminal sucrase activity. Measured su-crase activity of intraluminal contents was quitelow and could not account for the sucrose hydroly-sis, as has been reported by others (1, 8). How-ever, in addition, the sucrase activity of collectedsamples was not sufficient to explain the intra-luminal monosaccharide accumulation (Figure 5).This suggests that these monosaccharides werereleased from sucrose split by mucosa-bound en-zyme rather than from sucrose hydrolyzed bysucrase free in the intestinal contents.

It is of course possible that the in vitro sucraseassay of collected intestinal contents does not rep-resent the true sucrase activity in vivo. If intra-luminal sucrase were destroyed by a protease orby some other means after it had hydrolyzed itssubstrate, results of the sucrase assay would be

falsely low. However, sucrase activity did notdecrease appreciably when intestinal specimenswere incubated at 370 for 1 hour before assay(Table II). This suggests that there is negligibledestruction of intraluminal sucrase in the few min-utes required for the test solution to traverse the30-cm intestinal segment and therefore that thein vitro assay showing very low activity is a rea-sonable measure of intraluminal sucrase.

Oral meal studies. Since Dahlqvist and Borg-strom's finding of minimal absorption of sucrosein human jejunum was based on the use of a mealcontaining fat and protein as well as the disac-charide (1), four subjects were given the identicaloral meal and samples collected from a single lu-men tube placed at jejunal levels. As shown inTable III, 90 to 100% of the sucrose was ab-sorbed by the time the meal reached mid- to lowjejunal levels, and the small amount of sugar re-maining intraluminally was almost completely inthe form of monosaccharide products. Paper

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*SUCROSE 146 mMx SUCROSE 73 mM

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FIG. 3. INTRALUMINAL MONOSACCHARIDEAPPEARANCEAT DIFFERENT LEVELS OF INTESTINE

DURING SUCROSEINFUSION STUDIES. Both 73 mMand 146 mMsucrose studies are included,since values for the two groups were not significantly different. Monosaccharide appearance

indicates total glucose plus fructose accumulation found over the 30-cm test segment.

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INTESTINAL ABSORPTIONOF SUCROSEIN MAN

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180 200

FIG. 4. INTRALUMINAL MONOSACCHARIDEAPPEARANCEDURING SUCROSEABSORPTION. There is a low order of linearcorrelation (r = 0.51) between amounts of monosaccharides that appeared and of sucrose that was hydrolyzed.

chromatography by the method of Bickel (20-21)of the intestinal contents from the subjects giventhe meal verified the presence of glucose andfructose.

Discussion

The infusion studies demonstrated efficient hy-drolysis and absorption of sucrose in human je-junum at rates that were approximately twice as

rapid as in ileal segments. The extent of jejunal

absorption can be appreciated from Figure 2,which shows that an average of 50%o of the su-

crose infused was absorbed; this amounts to 22g per hour per 30-cm segment.

The meal studies showed almost complete ab-sorption of the ingested sucrose in jejunum, whichis in contrast to the minimal absorption (about15%) previously reported by Dahlqvist and Borg-strom (1). These markedly different results can-

not be ascribed to techniques of sugar analysis

TABLE I

Summary of sucrose infusion studies*

Mean Fraction of hy-intralu- drolyzed sucroseminal

Infusion monosac- AccumulatedNo. of concen- Sucrose Sucrose charide intralu-

Site studies tration hydrolysist absorptiont appearance minally Absorbed:

mM mmoles mono- mmoksmono- mmoks/hr % %saccharide/hr saccharide/hr

Jejunum 18 146 158 ± 30 128 :1: 26 30 19 81Ileum 13 146 82 ± 24 55 4 24 27 33 67

Jejunum 11 73 94 4 18 73 i 21 21 22 78Ileum 8 73 60 ± 14 37 4 8 23 38 62

* Values for hydrolysis and absorption expressed as mean ± SD.t Jejunal studies show statistically significant greater values than ileal (p < 0.001).t Jejunal studies show statistically significant greater values than ileal (p < 0.01).

0 DUODENUM* JEJUNUMX ILEUM

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GARYM. GRAYAND FRANZ J. INGELFINGER

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O S 1b 15 20 25 30 3s 40 45 50 5S 60INTRALUMINAL SUCRASEACTIVITY

(MMOLES MONOSACCHARIDEHR.)

FIG. 5. RELATIONSHIP OF INTRALUMINAL SUCRASEAC-

TIVITY TO ACCUMULATIONOF MONOSACCHARIDES(GLUCOSEPLUS FRUCTOSE) INTRALUMINALLY. Values above the di-agonal line are too great to be accounted for by intra-luminal sucrase activity.

since we found results by use of the dinitrosalicylicacid method (24) in these meal experiments to bewithin 10%o of those determined by our enzymaticassay.

The present studies showing rapid hydrolysisand absorption of sucrose in upper and mid-je-junum are compatible with the extensive humandisaccharidase assay experiments of Auricchio andco-workers (5) that demonstrated appreciablesucrase activity in jejunal mucosa obtained eitherby peroral biopsy or at surgery. Also supportingour findings are the data of a recent case report(2) of lactose intolerance in a patient who had a

normal blood sugar rise after the ingestion of su-

crose even though the ileum had been surgicallyremoved 3 months previously. Thus it appears

that the site of absorption of sucrose is no differentfrom that of other disaccharides (1, 25) and mono-

saccharides (26-28).It has previously been reported that intralumi-

nal sucrase activity cannot account for the rate ofdisappearance of sucrose from the intestine (1, 8).In addition, our studies demonstrate that intralu-minal sucrase activity also could not explain therate of appearance of the monosaccharide hydroly-

TABLE II

Effect of incubation of intestinal contentson sucrase activity*

Incubation timet before sucrase assay

Subject No incu-no. bation 1 hr 2 hr

1 4.0 4.8 5.02 1.9 1.53 3.6 3.4 3.2

[4 1.6 1.5 1.51.5 27 24 22

*Activity expressed as millimoles monosaccharide re-leased per hour per liter intestinal contents.

t Incubation at 370 C.

sis products in intestinal contents during the proc-ess of sucrose absorption. Apparently, therefore,the glucose and fructose that accumulated in intra-luminal contents were released from sucrose hy-drolyzed by mucosa-bound enzyme, and thesemonosaccharides then moved from the mucosalsurface to the lumen to be absorbed in the per-fused segment or at more distal intestinal levels.Sucrase has been shown to be localized at the lu-minal side of the epithelial cell in the brush border(29), and hence products released when sucroseis hydrolyzed might well have access to the lumen,especially if the absorbing mechanism for the re-leased monosaccharides were saturated.

Since sucrase activity is no different in jejunalor ileal mucosa (5), the slower hydrolysis ratesin ileum could possibly be explained by the factthat the surface area per unit length of intestine isconsidered to be less in ileum (30-32). However,a greater percentage of the released monosaccha-ride products was absorbed in jejunum than in

TABLE III

Sucrose-protein-fat meal*

%accumu-lated

intralu-%sucrose %sucrose minally

Tube hydrol- absorp- as mono-Subject positiont ysis tion saccharide

cmS. W. 130 99 93 6G. H. 150 100 92 8J. S. 1S0 100 100 0B. S. 160 100 98 2

* The meal contained 54 g sucrose, 22 g corn oil, 21 g eggalbumin, 1 egg yolk, and 4 g polyethylene glycol.

t Tube position refers to distance from teeth to collectingorifice.

396

7

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5

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1

INTESTINAL ABSORPTIONOF SUCROSEIN MAN

ileum, indicating that absorption lags proportion-ately further behind hydrolysis in ileum than injejunum. If surface area difference were the onlyimportant factor, a parallel decrease in both hy-drolysis and absorption would have been expectedat lower levels of intestine. Therefore some factoror factors other than mere surface area differencesprobably play a role in producing different absorp-tion rates from jejunum and ileum.

Lack of proportional change in hydrolysis andabsorption could have occurred if sucrose werehydrolyzed intraluminally in ileum by bacteria toa greater extent than in jejunum, thereby result-ing in an artificially high ileal hydrolysis rate.However, neither aerobic nor anaerobic sucraseassay, which should measure bacterial as well assuccus entericus enzyme activity, demonstratedthe intraluminal activity that would be necessaryto explain the proportionately greater accumula-tion of monosaccharides within the ileal lumen.

Summary

1) The site of intestinal absorption of the disac-charide sucrose was studied in normal man by theuse of both an oral meal and an infusion tech-nique. Contrary to current opinion, both hy-drolysis and absorption were quite efficient in hu-man jejunum. Furthermore, as demonstrated bythe infusion experiments, sucrose absorption rateswere considerably more rapid in jejunal segmentsthan in ileal segments (p < 0.001).

2) In addition to the lower rates of hydrolysisand absorption in ileum, absorption appeared tobe retarded even more than hydrolysis at ileal ascompared to jejunal levels of intestine. This sug-gests that a difference in surface area cannot ac-count by itself for the greater absorption rates injejunum.

3) During sucrose absorption appreciableamounts of glucose and fructose appeared in theintestinal lumen. The amounts of the monosac-charide products of sucrose hydrolysis that ac-cumulated could not be explained by intraluminalsucrase activity. These findings suggest that con-siderable amounts of glucose and fructose werereleased from sucrose hydrolyzed by mucosa-bound enzyme and that these monosaccharidesmoved from the mucosal surface to the lumen tobe absorbed subsequently.

Acknowledgments

The authors are grateful to Dr. Robert K. Crane formany helpful suggestions, to Dr. Normand Fortier forgenerous advice on the use of the hexokinase system, andto Mrs. P. Taggart and Miss P. Murray for technicalassistance.

References

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2. Kern, F., Jr., J. E. Struthers, Jr., and W. L. Attwood.Lactose intolerance as a cause of steatorrhea in anadult. Gastroenterology 1963, 45, 477.

3. Dahlqvist, A., and D. L. Thomson. The digestionand absorption of sucrose by the intact rat. J.Physiol. (Lond.) 1963, 167, 193.

4. Dahlqvist, A. Specificity of the human intestinaldisaccharidases and implications for hereditarydisaccharide intolerance. J. clin. Invest. 1962, 41,463.

5. Auricchio, S., A. Rubino, R. Tosi, G. Semenza, M.Landolt, H. Kistler, and A. Prader. Disacchari-dase activities in human intestinal mucosa. En-zymol. biol. clin. (Basel) 1963, 3, 193.

6. Fordtran, J. S., K. H. Soergel, and F. J. Ingelfinger.Intestinal absorption of D-xylose in man. NewEngl. J. Med. 1962, 267, 274.

7. Hirsch, J., E. H. Ahrens, Jr., and D. H. Blankenhorn.Measurement of the human intestinal length invivo and some causes of variation. Gastroenter-ology 1956, 31, 274.

8. Borgstrom, B., A. Dahlqvist, G. Lundh, and J.Sj6vall. Studies of intestinal digestion and ab-sorption in the human. J. clin. Invest. 1957, 36,1521.

9. Hyden, S. A turbidometric method for the deter-mination of higher polyethylene glycols in biologicmaterials. Ann. roy. Agr. Coll. Sweden 1955, 22,139.

10. Somogyi, M. Determination of blood sugar. J. biol.Chem. 1945, 160, 69.

11. Huggett, A. St. G., and D. A. Nixon. Use of glu-cose oxidase, peroxidase, and o-dianisidine in de-termination of blood and urinary glucose. Lancet1957, 2, 368.

12. Dahlqvist, A. Determination of maltase and iso-maltase activities with a glucose-oxidase reagent.Biochem. J. 1961, 80, 547.

13. Blecher, M., and A. B. Glassman. Determination ofglucose in the presence of sucrose using glucoseoxidase; effect of pH on absorption spectrum ofoxidized o-dianisidine. Analyt. Biochem. 1962, 3,343.

14. Schmidt, F. H. Die enzymatische Bestimmung vonGlucose und Fructose nebeneinander. Klin. Wschr.1961, 39, 1244.

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15. Beisenherz, G., T. Biicher, and K. Garbade. wyGlycerophosphate dehydrogenase from rabbit musclein Methods in Enzymology, S. P. Colowick andN. 0. Kaplan, Eds. New York, Academic Press,1955, vol. 1, p. 392.

16. Bernard, C. Du suc gastrique et de son r6le dans lanutrition. Thesis, University of Paris, 1843, vol.398, no. 242.

17. Keith, N. M., and M. H. Power. The urinary excre-

tion of sucrose and its distribution in the blood afterintravenous injection into normal men. Amer. J.Physiol. 1937, 120, 203.

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