Metabolic responses to fructose-1,6-diphosphate in healthy subjects.

Fructose-1,6-diphosphate (FDP) is an important naturally occurring intracellular metabolite with a direct regulatory role in many metabolic pathways. The most important and widely studied of the FDP effects has been its regulation of glycolysis, particularly the enzyme that synthesizes FDP--phosphofructokinase (PFK). Since it was observed experimentally that FDP does indeed modulate carbohydrate metabolism, we investigated whether FDP would similarly enhance carbohydrate utilization in man. The study used indirect calorimetry and was open to healthy adults (N = 45) of either sex and above legal age. After a steady metabolic state was obtained, 5 g of FDP (10%) was infused into a brachial vein. In 10 subjects, glucose (5 g) or FDP (5 g) was sequentially infused. The rapid intravenous infusion of FDP produced a slight but significant decrease in heart and respiration rates (P < .05). A significant increase in the serum concentration of inorganic phosphate (P < .0001) and the intraerythrocytic concentration of adenosine triphosphate (ATP) (P < .01) was also observed. The FDP infusion produced a decrease in plasma cholesterol and triglycerides (P < .001 and P < .01, respectively). The indirect calorimetric data indicate that the infusion produced a highly significant increase in the respiratory quotient ([RQ] P < .0001) and the energy derived from carbohydrates (P < .0001) and a significant decrease in the energy derived from lipids (P < .0001). Glucose infusion did not cause changes in any of the parameters. These data indicate that carbohydrate metabolism is stimulated by FDP.