Clinical Science (1973) 44, 425-428.
SHORT COMMUNICATION
COMPARISON OF ABSORPTION RATES O F GLUCOSE
A N D MALTOSE I N M A N I N V I V O
G. C. C O O K
Department of Medicine, The University of Zambia, Lusaka
(Received 22 December 1972)
SUMMARY
1. Using a double-lumen tube perfusion technique in vivo, the absorption rates of
glucose from a glucose (200 mm011-~)and from a maltose (100 mmol 1-I) solution
were measured in the proximal jejunum of six Zambian African adults.
2. In all of the subjects the rate of glucose absorption from the maltose solution
was greater than that from the glucose solution. The difference between the mean
rates was approximately 15% and is significant (P<O.Ol).
Key words : disaccharide absorption, glucose, maltose.
Polysaccharide, mainly in the form of starch, constitutes the bulk of the diet of most Zambian
Africans. It is not clear whether maltose, and sucrose, have a greater rate of disappearance
from the lumen than their constituent monosaccharides (McMichael, Webb & Dawson,
1967; MacDonald & Turner, 1968; Matthews, Craft & Crampton, 1968; Cook, 1970).
In the present investigation a double-lumen tube perfusion system was used to compare the
jejunal absorption rates of glucose from glucose and from maltose in a group of Zambian
African adults.
SUBJECTS A N D M E T H O D S
The subjects were six Zambian Africans who were in-patients at The University Teaching
Hospital, Lusaka; they volunteered to undergo investigation after full explanation through
an interpreter. None of them had clinical evidence of malnutrition or of gastro-intestinal
disease. Two were men; the mean age was 40 (17-60) years and mean body-weight 53 (44-66)
kg. They were from the Bemba, Inamwanga, Chokwe, Kaonde, Soli and Lenje tribes of Zambia
(Brelsford, 1965). The mean haemoglobin concentration was 12.0 (7.9-13.7) g 100 mi-'.
Correspondence: Professor G. C. Cook, Department of Medicine, The University of Zambia, P.O. Box 2379,
Lusaka, Zambia.
425
426
G. C. Cook
Mean serum protein concentrations were : albumin 3.5 (3.1-4*0),total globulin 4-2 (3-3-5-3),
and y-globulin 2-2 (1.7-3.0) g 100 ml-'. Five of them had stool examinations for parasites,
which were normal.
A double-lumen tube (Portex MLT/B, external diameter 4.2 mm) was used and the perfusion
technique has been described (Cook, 1971a, 1972b). Radiographs were taken immediately
before and after the study and in no case had the proximal end of the 30 cm perfusion segment
moved by more than 10 cm distally; the mean position at the beginning of the study was 11
(1-22) cm past the ligament of Treitz.
Perfusion was with a 200 mmol 1-' glucose solution, and a 100 mmol 1-l maltose (Hopkin
& Williams, England) solution. Both solutions were rendered iso-osmotic with sodium
chloride and they contained 0.50 g 100 ml-I of polyethylene glycol (PEG), mol. wt. 4000. The
maltose solution contained <50 mg of glucose 100 ml-' by the hexokinase method (see below).
In three subjects the glucose solution, and in three the maltose solution was infused first. The
two perfusions followed immediately after each other.
Aliquots of all samples were immediately deproteinized (Marks, 1959) and they and the
remainder were frozen solid until estimation. Glucose was determined before and after incubation for 90 min at 37°C with a maltase (Sigma M-2125) suspension, by a glucose oxidase
method (Boehringer, Mannheim G.m.b.H.). Maltose was hydrolysed during the glucose
oxidase reaction; glucose in the samples containing maltose was therefore determined by a
hexokinase method (Slein, 1965). Glucose oxidase and hexokinase determinations were also
done after exposure of the samples to room temperature ( ~ 2 7 ' C )for 6 h ; in no case was there a
detectable difference. Total carbohydrate concentrations in the glucose samples were determined by a copper reduction method using glucose standards (Asatoor & King, 1954). PEG
concentrations were estimated by the method of HydCn (1955). Specimens of all perfusion
solutions were treated as the test samples. All determinations were made in duplicate.
Correlation of glucose oxidase and copper reduction results on samples obtained during
the glucose perfusions was significant (u = +0.989; n = 17; y = 1-037x-0.010).
Absorption rates were calculated using standard formulae (Cook, 1971a). For glucose
absorption from glucose the SD for the three 10 min collections was 0.014 g min-' (30 cm of
jejunum)-' (a = 6); coefficient of variation = 6.1% (Cook, 1972a). For glucose absorption
from maltose the corresponding values were 0.009 g min-l (30 cm of jejunum)-' (n = 6), and
3.4%. For net water absorption the SD was 0.42 ml min-' (30 cm of jejunum)-' (n = 12).
The rate of glucose production (by hydrolysis) during the maltose infusions was similarly
calculated; the concentration of unhydrolysed maltose was obtained by subtracting the
hexokinase from the glucose oxidase result.
RESULTS
No symptoms were reported. Fig. 1 summarizes data for glucose absorption rates. In all
subjects the absorption rate was higher from the maltose solution; the difference between the
means is significant (t = 5.65; 5 degrees of freedom; P<O.Ol, paired t-test). The subject with
the highest absorption rates had the highest serum albumin and lowest total and y-globulin
concentrations. Fig. 1 also shows the mean net water absorption rates; the difference between
them is not significant ( t = 1.20; 5 degrees of freedom; P>O.lO, paired t-test).
In all of the subjects the rate of glucose production from maltose exceeded its absorption
Glucose and maltose absorption in man
427
2-
C
._
c
E
n
5:
I-
L
z
0)
(a 1
01-
( b)
0
FIG.1. Glucose absorption rates (a) [g min-' (30 cm of jejunum)-'] from the glucose (0)and
maltose (A) solutions. The means + 1 SEM are shown. The difference between the means is
significant. The means +_1 SEM are also shown for net water absorption rates (b) [ml min-'
(30 cm of jejunum)-'] from the glucose (0)and maltose (A) solutions. The difference between the
means is not significant.
rate. The mean rate of glucose production was 0-35 g min-l (30 cm of jejunum)-' (SEM =
0.01). The difference between mean production and absorption rates is significant (t = 11.40;
5 degrees of freedom; P<O.OOl, paired t-test).
DISCUSSION
This study shows that glucose was absorbed at a significantly greater rate from a 100 mmol
1-1 maltose solution than from a 200 mmol 1-1 glucose solution.
Gray & Santiago (1966) showed that in ten normal subjects the mean rate of glucose
absorption was 10% higher from a maltose (80 mmol 1-l) than from a glucose (160 mmol
1- l) solution; that difference was not, however, significant. McMichael et al. (1967) similarly
demonstrated that glucose absorption rates from glucose and maltose solutions (0-5-10.0 g
100 ml-l) were comparable. Using oral 'tolerance', Matthews et al. (1968) showed in nine
healthy subjects that after 90 g of glucose per 70 kg body weight, or its equivalent as maltose,
blood-sugar curves were very similar. Comparing sucrose with its constituent monosaccharides
in man, Gray & Ingelfinger (1966) and Cook (1970) were unable to detect differences between
the rates of absorption and blood monosaccharide responses, respectively. On the contrary,
MacDonald & Turner (1968) using oral 'tolerance' showed in eighteen healthy subjects that
the mean area under the blood fructose curve was 3040% greater after sucrose compared
with its monosaccharides; the difference was significant. In the rat, Dahlqvist & Thomson
(1963a, b) found no difference between absorption rates of maltose and sucrose and their
respective monosaccharides. The reason for these widely differing results is unknown. The
sugar concentrations used in the present study were relatively high when the Kt for a 30 cm
segment of jejunum is taken into account (Cook, 1971b). Zambian Africans live largely on
starch and it is possible that this could account for differences from European subjects;
genetic or other acquired bases could also be responsible.
After hydrolysis of maltose in the brush-border of the enterocyte, a high glucose concentration must be produced in the vicinity. Glucose absorption is a saturable process in Zambian
428
G. C. Cook
Africans (Cook, 1971b). With 200 mmol glucose I-' the kinetic curve has not yet reached a
plateau and after maltose hydrolysis the higher local glucose concentration would be expected
to lead to a greater absorption rate; the remainder of the glucose (from hydrolysis) would
diffuse back to the lumen. The present results are consistent with that hypothesis.
The study does not exclude the possibility of separate transfer mechanisms for mono- and
di-saccharides, as for amino acids and dipeptides (Cook, 1973; Matthews, 1971), nor the
possibility that some intact maltose may enter the enterocyte.
ACKNOWLEDGMENTS
I am grateful to Mr James Tembo for his help with the patients. The Reverend W. H. Woodhouse provided generous financial support.
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