Effect of fructose feeding on the activity of enzymes of glycolysis, gluconeogenesis, and the pentose phosphate shunt in the liver and jejunal mucosa of rats.

The influence of fructose feeding for 1 to 12 days on the activity of enzymes of glycolysis and gluconeogenesis was studied in the jejunal mucosa and the liver of rats. In the jejunal mucosa fructose feeding leads to an increase in the activity of 6-phosphofructokinase (p less than 0.05) and fructose-1.6-bisphosphate aldolase (p less than 0.05), while the activity of hexokinase and glucose-6-phosphate dehydrogenase remains unchanged. Fructose feeding increases the activity of fructose-bisphosphatase in the jejunal mucosa, however, the absolute values of this enzyme remain low (less than 10%) when compared to those in the liver. In the liver fructose feeding is followed by a marked increase of the activity of fructose-bisphosphatase and glucose-6-phosphate dehydrogenase. In contrast, the activity of glucose-6-phosphatase decreases significantly under a fructose enriched diet. The enzyme activity rose to a maximum within 3 days; in the following time of observation no major changes occurred. The results are in accordance with the assumption that fructose feeding leads in the jejunal mucosa mainly to adaptive alterations of the activity of those enzymes which are involved in the breaking-down of fructose, whereas in the liver the activity of those enzymes is increased, which take part in the new synthesis of glucose-6-phosphate or which direct glucose-6-phosphate into the pentose-phosphate.