Comparative effects of some carbohydrates on serum sugars, triglycerides and digestive hydrolases
Comparative effects of some carbohydrates on serum sugars, triglycerides and digestive hydrolases
NOIROT Malika OUAGUED Anik GIRARD-GLOBA 0
0 Centre de Recherches
Summary. For 3 weeks, rats were fed diets containing 60 p. 100 carbohydrate in the form of starch (wheat flour), purified sucrose, commercial sugar or a commercial sweetner containing a mixture of glucose and fructose. Glycemia was lower during the day than at night, and it was lowest in the starch-fed group. Fructosemia, high in all groups during the day, suggested endogenous production ; it was low at night, showing efficient clearance of exogenous fructose. Triglyceridemia was highest in the rats fed purified sucrose and exhibited no light/dark variation in that group. It was higher in all the other groups during the day.
kin, 1963 ; Thompson et al., 1979 ; Michaelis et al., 1975). Aside from the work of
Bruckdorffer et al., most authors studying metabolic effects reported only one
measurement per day and did not take into account the shift in metabolism from nocturnal
glycogenogenesis to diurnal glycogenolysis and lipogenesis. Assuming that fructose
could be handled differently by the organism, depending on whether it is present as a
monosaccharide or a disaccharide, we compared diurnal and nocturnal levels of
glycemia, fructosemia and triglyceridemia in rats fed diets containing sucrose, a mixture
of glucose and fructose, or starch. Since circulating metabolites seem to be partly
responsible for adapting pancreatic secretion to the diet
(Ben Abdeljlil and Desnuelle,
1964 ; Lavau et al., 1974)
, we also compared levels of pancreatic hydrolases and
Michaelis and Szepesi (1974) suggested that some of the discrepancies in the results
might be due to the quality of the dietary carbohydrate. Commercial sugar is often
used in semi-purified diets, while fructose and glucose are purified sugars. For this
reason, we also compared sucrose to commercial sugar.
Material and methods.
Sixty-four Wistar male rats, weighing 100 g, were divided into 4 groups, each
receiving one of the diets (table 1) containing a different type of carbohydrate (starch,
commercial sugar, purified sucrose or a commercial sweetner containing 50 p. 100
glucose, 42 p. 100 fructose, 8 p. 100 maltose and traces of polydextrins). These diets
were fed for 21 days during which the animals were weighed at regular intervals and
their food intake recorded.
At the end of the experimental period, the rats were killed by aortic
exsanguination under light ether anesthesia. Half in each group were killed between 14.00 and
16.00 hrs. (light period) and the other half between 02.00 and 04.00 hrs. (dark period).
The serum was collected and the pancreas and liver excised and frozen until assay ;
the intestine was also kept frozen after its contents had been washed away with an
icecold solution of 0.9 p. 100 NaCI.
Serum glucose was determined by glucose-oxidase (Trinder, 1969) and serum
fructose by the zirconium chloride procedure of Schlegelova and Hruska (1977): The
value measured was corrected for a small glucose interference in the assay by
subtracting from the apparent fructose measurement the value obtained with an amount of
glucose equivalent to sample glycemia.
Serum cholesterol was determined according to
Abell et al. (1952
) and triglycerides
by the enzymatic method of Wahlefeld (1974).
The pancreatic tissue was homogenized in 10 volumes of ice water. Amylase
activity was determined as described by
) ; chymotrypsinogen was
activated with trypsin and its activity measured on the synthetic acetyl-tyrosine-ethyl-ether
); measuring the release of acetic acid by continuous
titrimetry on a Metrohm pH stat with 0.02 N sodium hydroxide. Lipase activity was
estimated by a method based on the one described by Marchis Mouren, Sarda and Desnuelle
(1959) at pH 9.0 using a triolein substrate stabilized with gum arabic (triolein 45 ml,
10 p. 100 gum arabic 360 ml). The homogenate sample was added to 7ml of substrate
with 1 ml of buffer (NaC1375 mM, CaCi, 75 mM) and 1 ml of 10 p.100 Na
tauroglycocholate. Under such conditions. lipase alone is inactive and requires colipase. A crude
preparation of colipase was added to ensure full expression of lipase activity. The
colipase contents of the sample were determined by an identical procedure, except i-hat to
destroy endogenous lipase activity the reaction mixture was brought to pH 2 with 1 N
HCI after addition of the sample. After the pH was restored to 9.0, a purified
preparation of lipase was added and the colipase was estimated from the amount of lipase
Intestinal saccharose was measured by the method of
) on samples
of 1 p. 100 tissue homogenates.
Food ingestion and weight gain. - After an initial adjustment period, all the groups
fed identically. The rats receiving starch or commercial sugar gained significantly more
(P < 0.01) than those fed purified sugar or commercial sweetner, but the differences
did not exceed 10 p. 100 (fig. 1).
Plasma glucose and fructose. - In all the groups, glycemia was significantly higher
during the digestive period at night than during the day (table 2). The highest levels
were reached with the commercial sugar diet. The starch-fed rats had the lowest blood
glucose, and the difference was most marked during the day when glycemia decreased
in this group more than in those fed any of the sugars (P < 0.01).
Fructosemia (table 2), high during the day (36 to 58 mg per 100 ml), was not any
lower in the rats fed starch than in those receiving the sugars containing fructose. It was
low at night, not exceeding 10 mg per 100 ml, except in the rats fed commercial sugars
and showing a significantly higher fructosemia than all the other groups (P < 0.01).
Plasma triglycerides. - Triglyceridemia (table 2) was lower at night, but owing to
individual variation, the difference was significant only in the rats fed the
glucosefructose mixture (P < 0.01). The animals fed purified sucrose exhibited no diurnal
variations and had uniformly high triglyceridemia. As expected, all the groups fed
sugar had higher lipid levels than the starch controls, particularly during the day when
triglyceridemia was most elevated.
Pancreatic hydrolases. - Amylase activity of the pancreatic tissue was significantly
lowered by sugar feeding as compared to starch feeding (table 3). Chymotrypsinogen
was significantly decreased (P < 0.01) by commercial preparations of both sugar and
Lipase activity was slightly higher in the sugar-fed rats but reached only a
moderately significant level (P < 0.05). Colipase was not significantly different in any of the
g rou ps.
Intestinal sucrase. - Sucrase activity was significantly higher at night in all groups
(table 4), but was highest in the starch and sweetener-fed animals. It was significantly
lower in the other two groups, but particularly in that fed the purified sugar whose
values differed from those of the other groups (starch, P < 0.01 ; sweetener, P < 0.01;
commercial sugar, P < 0.05).
Feeding apparently equivalent sugar diets resulted in metabolic effects which were
not identical in all respects at either the level of circulating metabolites or that of
Circulating glucose levels were high in all groups, even in those fed starch, because
the animals were not fasted prior to killing. Glycemia was higher at night (02.00 to
4.00 hrs.) than during the day (14.00 to 16.00 hrs.). This result is in agreement with the
findings of Peret et al. (1973), although
Jolin and Montes (1973
) reported a maximum
around 18.00 hrs. and
Gagliardino and Hernandez (1971
) found maximal glycemia in
mice between 8.00 and 12.00 hrs. The variation between day and night was more
marked with the starch diet, the day/night ratio being 0.74 vs 0.80, 0.89 and 0.86 with the
three sugar diets. The smaller amplitude of variation in sugar-fed rats was essentially
due to the higher daytime levels when the animals were eating very little. Such poor
blood glucose clearance during the period of relative fasting might indicate a diabetic
tendency, as was evidenced by
Bruckdorffer, Khan and Yudkin (1972
), or to a
perturbation in the light/dark pattern of insulinemia (Kalopyssis et al., 1979), consecutive to
prolonged sugar feeding.
Fructosemia was about 10 mg per 100 ml during the night, which is within the
range of values found by
Bruckdorffer et al. (1974
). However, the daytime values were
unexpectedly high. The zirconium chloride assay method was checked and shown to
give results closely agreeing with the resorcinol technique of Roe (1934) employed by
Bruckdorffer et al. (1974
). The only substance which could react in the same manner is
sorbitol but it is highly unlikely that significant amounts would be found in the serum.
Since fructosemia was significantly elevated, even in the starch-fed rats, it is probable
that the fructose was of endogenous origin and should be investigated further.
Bruckdorffer et al. (1974
) also found a rise in fructosemia during the day, but it was of much
lower amplitude. The same authors also reported a reversed pattern in sucrose-fed
animals which did not occur in our experiment. However, sugar-fed rats did exhibit
very high nocturnal fructose values as compared to the other groups. Compared to
daytime values, the relatively low nocturnal levels of fructosemia are surprising in animals
fed sucrose, sugar or glucose-fructose. The digestive processes by which fructose is
absorbed are only partially clarified at present. According to Rerat et al. (1978)
studying swine, fructose appears in the portal vein, during sucrose digestion, in less than
equimolar amounts as compared to glucose. This can be taken to mean that either
fructose is absorbed more alowly than glucose, or rather that it is rapidly converted to
glucose or to fatty acids by the enterocyte before it can appear in the circulation. In
the present experiment where only peripheral concentrations were measured, the
liver may have contributed further to fructose clearance. In this respect, it is interesting
to compare the fructosemia and triglyceridemia levels in the rats fed commercial or
purified sucrose. In the former, fructosemia remained very high at night, while
triglyceridemia was moderate. In the latter, on the contrary, fructosemia was as low as in the
other groups at night but triglyceridemia was considerably elevated. This emphasizes
that a balance occurred between the two metabolites, and indicates that some
contaminant in commercial sucrose may partially impair the ability of the liver to convert
fructose to fatty acids. In rats fed the glucose-fructose mixture, nocturnal clearance of
fructose was very efficient but triglyceride output was low. Thompson et al. (1979) also
reported a « disaccharide effects in humans by which a mixture of glucose and
fructose raises plasma triglycerides significantly less than an equivalent amount of sucrose.
One possibility in that case is that, in the presence of glucose, the monosaccharide form
of fructose is more efficiently converted to glucose than the disaccharide form and is
therefore less lipogenic. In favour ofthis hypothesis is the fact that pancreatic amylase,
which responds to glucose, was particularly high at night. On the whole, fructose was
more efficiently cleared from the plasma than glucose. It is unlikely that this was due to
poorer absorption since the animals on sugar gained as much weight as those on starch
with a similar caloric intake. More likely, the fructose disappeared quicker because it
was more readily taken up by the liver (Sillero et al., 1969).
The investigation of a few key digestive hydrolases has yielded some interesting
results. It is usually accepted that pancreatic amylase responds to glucose as well as to
(Ben Abdeljlil and Desnuelle, 1964)
Deschodt-Lanckman etal. (1971
that saccharose stimulated amylase to the same extent as starch, while
) reported lower levels. Our results agree with the latter and confirm the
hypothesis that it is the glucose moiety of saccharose which acts on amylase production.
But, in our study, blood glucose was, if anything, higher in the sucrose and sugar
groups than in the starch group. It is therefore likely that if glucose is responsible for
amylase induction, it must act at the intestinal level by a receptor mechanism such as
that postulated in the rat by
Dick and Felber (1975
) and in swine by Simoes Nunes and
Corring (1979). As we have seen above, rats fed the glucose-fructose mixture had a
higher amylase level at night which might be due to more efficient conversion of
fructose to glucose than in the disaccharide form. An incidental finding was that both
commercial preparations significantly decreased pancreatic chymotrypsinogen contents,
although protein intake was not diminished. It would be interesting to find out whether
some minor contaminant due to industrial treatment might not be responsible for this
effect since there is no significant nutritional difference between the sucrose and sugar
Bucko, Simko and Kopec (1969
) have reported an increase in lipase activity
consecutive to sucrose feeding which they attributed to hyperlipemia. Our results do
not support these findings as we observed no change in either lipase or colipase
activity, despite a marked hyperlipemia.
The intestinal enzymatic complex of saccharase-isomaltase shows a clear-cut
diurnal rhythmicity (Saito et al., 1976) which we have evidenced in all the groups. In
our experiment, only sucrase activity was measured, but it is known to be induced by
starch in parallel with isomaltase (Kolinska and Kraml, 1972). In the rats fed starch, it
is not astonishing therefore to find high levels of sucrase which we interpreted as
digestive adaptation to isomaltase. When the rats were fed purified sucrose, however, both
the daytime base level and the nighttime stimulated level were decreased. Saccharase
activity was slightly higher in rats fed commercial sugar, and in sweetener-fed rats it
reached the values found with starch. This may mean that sucrose per se is not as good
an inducer of the enzyme complex as starch, and that the small amounts of maltose or
polydextrins contained in commercial sugar or sweetener may contribute to further
Regu en janvier 1981.
Accept6 en avril 1981.
Résumé. Des rats ont reçu pendant 3 semaines des régimes contenant 60 p. 100 de
glucides sous la forme soit d’amidon (farine de blé), de saccharose purifié, de sucre du
commerce, ou d’un édulcorant contenant un mélange de glucose et de fructose. La glycémie est
plus basse pendant la période diurne que la nuit, surtout dans le groupe à l’amidon. La
fructosémie est élevée en période diurne dans tous les groupes ce qui suggère une origine
endogène. Elle est basse la nuit témoignant d’une bonne métabolisation du fructose exogène.
Les rats nourris au saccharose ont une triglycéridémie élevée mais sans variation
nycthémérale. Dans les autres groupes la triglycéridémie est plus élevée en période diurne.
Au niveau des hydrolases pancréatiques, l’amidon augmente l’amylase plus que les
sucres, tandis que la lipase n’est pas corrélée avec l’hypertriglycéridémie endogène. Les
préparations commerciales (sucre et édulcorant) abaissent significativement le
Ces résultats confirment la non-équivalence entre le saccharose et les mélanges
équimolaires de glucose et de fructose (effet disaccharide). Ils mettent en évidence une
production endogène de fructose pendant la journée et suggèrent que le sucre commercial, souvent
employé dans la préparation de rations semi-synthétiques, pourrait avoir des effets un
peu différents de ceux du saccharose purifié.
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