The rates of intestinal transport of dietary monosaccharides and disaccharides were determined in Wistar rats and the carbohydrate-sensitive BHE rats fed either a stock diet or a 65% sucrose diet. Sucrose-fed rats of both strains generally showed large and significant increases in the rates of glucose, alpha-methylglucose, fructose, and sucrose transport. The transport of galactose, maltose, and lactose did not show consistent increases due to sucrose feeding. Although the magnitude of the increases in sugar transport due to sucrose feeding was only slightly greater in BHE rats than in Wistar rats, BHE rats tended to exhibit a greater rate of sugar trnasport when fed both strains and in the BHE rats fed the stock diet. Lipogenic enzyme activity was greatly increased as a result of sucrose feeding; however, BHE rats did not show greater levels of enzyme activity than did Wistar rats. Liver lipids were increased in both the Wistar and the BHE sucrose-fed rats and in BHE rats fed either diet.
The degree to which the rat stomach empties carbohydrate in preference to fat was studied in rats fed a diet or various test means providing carbohydrate and fat in a 3:1 (w/w) ratio. When rats were adlibitum fed a glucose-containing diet, the glucose:fat ratio in gastric contents was consistently lower than in the diet and was 10% as great at noon as at midnight. When starved rats were fed a single meal of the same diet the average fractional emptying rate for carbohydrate exceeded that for fat; and the ratio of these rates ("the gastric emptying ratio") was essentially the same when calculated from gastric contents observed 1, 2, 4, or 6 hours after the test meal. The gastric emptying ratio was also not changed when test means were made with hard, soft, or liquid fat or with no or extra protein (lactalbumin). Use of finely divided glucose monohydrate, dried crystalline glucose or of cornstarch resulted, respectively, in high, intermediate and low gastric emptying ratios. The kind and form of carbohydrate in the meals and the ease of its extraction with water appear to be important factors governing the degree to which carbohydrates is preferentially emptied from the stomach.
Sprague-Dawley rats were briefly starved, fed various test meals, and killed at measured intervals, and the average fractional emptying (disappearance from stomach) rates for glucose (Kgl) and for fat (Kfat) were determined. The Kgl/Kfat ratio was calculated as a measure of the degree to which the stomach emptied glucose preferentially to fat. The size of the meal affected this ratio, which was 7.6 for a small (0.5 g) meal and 2.4 for a large (2.0 g) meal of a nutritionally complete diet. When test meals contained one of two levels of fat (0.4 and 0.1 g) and of glucose (1.2 and 0.3 g), the high level of fat depressed Kgl and Kgl/Kfat, whereas the high level of glucose depressed Kgl and particularly Kfat and, therefore, raised Kgl/Kfat. Kgl/Kfat was also affected by strain of rat and was reduced almost to 1.0 by mixing the meal into a viscous gel of xanthan gum. In the absence of this gel, the percentage of water existing in stomach contents shortly after the test meals varied between 53 and 79% and was suspected of influencing Kgl/Kfat.
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