Glucoregulatory response to intravenous fructose administration in the dog

This study was designed to evaluate the influence of fructose administration on glucose kinetics and the role of fructose conversion to glucose in the maintenance of glucose homeostasis. Intravenous fructose infusion (4.5 mg/kg min-1) produced a stable plasma fructose concentration of about 20 mg/dl and a small but sustained decrease (10 mg/dl) of plasma glucose levels. The latter effect was entirely attributable to a rapid 30-35% fall in hepatic glucose output which later returned slowly to pre-infusion levels. No significant change in the rate of glucose utilization was observed. The rate of fructose conversion to glucose rose progressively during fructose infusion reaching a plateau of 1.4 mg/kg min-1 which corresponded to about 40% of total glucose production. Furthermore, as much as one third of the infused fructose was converted to circulating glucose. No appreciable changes in plasma insulin and glucagon levels occurred during fructose infusion while plasma alanine concentration increased remarkably. These data indicate that 1) fructose administration induces a transient fall in endogenous glucose production not accompanied by significant changes in glucose utilization; 2) the rapid conversion of the infused fructose to circulating glucose provides for the restoration of normal rates of glucose production; and 3) the glucoregulatory response to the administration of fructose occurs in the absence of detectable changes in plasma pancreatic hormone concentration.