The effect of fructose feeding on glycolytic enzyme activities of the normal rat liver.

A number of studies have brought to light the fact that substitution of fructose for glucose as the sole carbohydrate in a diet results in a profound change in the metabolic behavior of an animal. Thus, the ability of the liver of a glucose-fed, diabetic rat to convert acetate carbon to fatty acids is considerably impaired (l), but when the glucose of the animal’s diet is replaced by fructose, hepatic lipogenesis from acetate is restored to normal (2). Later studies of Hill et aZ. (3, 4) revealed that normal rats and dogs fed a diet containing 58 per cent fructose as sole carbohydrate develop an impaired capacity for utilizing glucose. In order to localize the site of defective glucose utilization in the fructose-fed rat, Hill et al. (3) compared glucose-fed and fructosefed rats with respect to (a) oxidation of W-glucose to CO2 by kidney and brain slices; (b) glucose uptake by the diaphragm; and (c) conversion of Cl*-glucose and W-fructose to COZ, fatty acids, and glycogen by slices prepared from the livers of these rats. Fructose feeding did not alter the oxidation of glucose to CO2 by kidney and brain, nor the uptake of glucose by the diaphragm. The liver was the only tissue in which an alteration in metabolic pattern was found after fructose feeding. Impaired glucose utilization has also been observed in the livers of human subjects fed fructose (5). The mechanism by which fructose feeding induces a metabolic change in the liver is not known. The loss in the liver’s capacity to utilize glucose, observed in normal rats fed fructose, is not the result of an insulin lack, for the injection of insulin subcutaneously for 3 days failed to increase that capacity (3). To further our understanding of the effects of fructose feeding we have studied glycolytici enzyme activities of livers of normal rats fed fructose or glucose as sole carbohydrate in the diet.