Efectos de la corrupción

From the above results it was inferred that tea polyphenols might inhibit, in vivo, the digestion of starch and sucrose and suppress blood glucose levels. To verify this hypothesis, de- tailed hypoglycemic experiments were conducted with rats (3). Various amounts of green tea catechin (GTC) were adminis- tered to rats followed by a full but tolerable amount of saccha- rides 30 min afterward. At intervals over two hours after saccharide administration, plasma glucose and insulin con- centrations, as well as intestinal enzyme activity, were mea- sured.

Male wistar strain rats weighing 180 to 200 g (six weeks of age) were fed a commercial diet for one week. The rats were divided into four groups of 20 and starved overnight. GTC so- lutions of 80, 60, and 40 mg/ml were administered orally in 1 ml doses to each group of rats. Water was administered to the control group. After 30 min, 4 ml of 40% soluble starch solution was administered orally to all the rats. Immediately after ad- ministration and at 30 min, 1 hour, and 2 hour intervals, rats from all groups were killed and their blood was collected. The same procedure was followed for sucrose; with GTC solutions of 80, 10, and 5 mg/ml being administered to the test groups, followed by 4 ml of the 40% sucrose solution 30 min afterward. In order to see the effect of catechins on the digestion of glu- cose per se, one group of rats were administered glucose in- stead of starch or sucrose.

The results showed that when 80 or 60 mg of GTC were given 30 min before the administration of starch, the increase of glucose and insulin concentrations in the plasma was sig- nificantly suppressed as compared with those of the control group (Fig. 1). However, when 40 mg of GTC was given before starch administration, there was only slight suppression, demonstrating that suppression was dependent on the quan- tity of catechins administered to the rats. In the case of su- crose, 80 mg of GTC significantly suppressed the rise of glu- cose and insulin levels in the plasma which would otherwise have been elevated by sucrose (Fig. 2). Similar effects were observed with 10 mg of catechin administration, but no effect

was observed with 5 mg of GTC. As expected, intestinal α-

amylase activity of the catechin group (80, 60, and 40 mg) scarcely increased during the 2 hour period after administra- tion of starch, but the enzyme activity of the control group in- creased markedly after the starch dosing(Fig. 3).In the same way, sucrase activity in the catechin groups (80, 10, and 5 mg) was significantly lower than that of the control group(Fig. 4).

In the case of the glucose-administered group, the plasma glu-

FIG. 2 Glucose concentration in blood plasma of rats administered su- crose.

FIG. 4 Sucrase activity in intestine of rats administered sucrose.

cose level increased, regardless of whether catechin had been administered or not.

The results showed inhibition ofα-amylase in the intes- tine, which was presumably responsible for the resultant sup- pression of plasma glucose and plasma insulin levels. There appears to be a certain threshold concentration for catechin to suppress plasma glucose levels. Simultaneous administra- tion of starch with catechin had similar results (data not shown). Sucrase activity and plasma glucose levels were af- fected in the same way by prior or simultaneous administra- tion of catechin with sucrose. The difference between the inhi- bition patterns ofα-amylase and sucrase further indicates the interaction of these enzymes with catechin. As seen inFig. 3,

sinceα-amylase is secreted when starch enters the duodenum, there was hardly any difference between inhibition in the con- trol and catechin-fed groups immediately after starch admin- istration (0 min). At 30 min, when starch was present in the duodenum, enzyme activity peaked and was markedly inhib- ited by varying doses of catechin. On the other hand, sucrase

is always present on the brush border membrane of the small intestine. Results in Fig. 4 show a definite inhibition of su- crase at 0 min, suggesting that the 30 min prior catechin dos- ing worked to suppress sucrase regardless of sucrose adminis- tration. Plasma insulin concentration increased proportionate to that of plasma glucose, and both were duly suppressed by catechins.

Throughout these experiments, it was postulated that in- hibition of enzymes by tea polyphenols plays a key role in sup- pression of plasma glucose levels. Accelerated insulin secre- tion or the deterrence of glucose absorption from the bloodstream into the body, are other possible factors that can suppress increases in plasma glucose levels. However, it was confirmed in previous experiments that catechins have no in- fluence on these factors (data not shown). In the same way, when glucose was given, catechin administration brought about no change in the pattern of plasma glucose level varia- tions. It could be concluded from these experimental results that the inhibition of the above α-glycosidases by catechins was realized in the small intestine of rats and as a result, when a surfeit of starch or sucrose was administered, an in- crease in glucose levels was suppressed. In another series of experiments, it was confirmed that the amount of feces on a dry weight basis increased to nearly twice as much as that of the control in rats fed catechins over one month (4). This in- crease was found to gradually level off over a longer period of catechin feeding, indicating that there is a certain degree of

supplemental secretion of α-amylase. It was also confirmed

that as much as 1 or 2% catechin in the diet, fed over a period of three months, did not reduce body weight gains(Fig. 5)or food intakes (Fig. 6) as compared with those of control rats. These results indicate that the possible indigestibility of cate- chins would not cause any malnutrition. Detailed feeding ex- periments over a longer period are necessary to examine the influence of catechins on the absorption and excretion of carbo- hydrates in rodents as well as in humans.

FIG. 5 The effect of GTC on body weight in rat fed diet containing GTC for three months.

FIG. 6 The effect of GTC on food intake in rat fed diet containing GTC for three months.

REFERENCES

1. Y Hara, M Honda. The inhibition ofα-amylase by tea polyphe- nols. Agric Biol Chem 54:1939–1945, 1990.

2. Y Hara, M Honda. Inhibition of rat small intestinal sucrase and

α-glucosidase activities by tea polyphenols. Biosci Biotech Bio- chem 57:123–124, 1993.

3. N Matsumoto, F Ishigaki, A Ishigaki, H Iwashina, Y Hara. Re- duction of blood glucose levels by tea catechin. Biosci Biotech Biochem, 57:525–527, 1993.

4. K Muramatsu, M Fukuyo, Y Hara. Effect of green tea catechins on plasma cholesterol level in cholesterol-fed rats. J Nutr Sci Vitaminol 32:613–622, 1986.

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Hypotensive Action of Tea