Plasma D-glucose, D-fructose and insulin responses after oral administration of D-glucose, D-fructose and sucrose to normal rats.
OBJECTIVE
To assess whether oral D-fructose modifies the plasma D-glucose and insulin responses to oral D-glucose administration in normal rats.


METHODS
Oral D-glucose (1.7, 3.5, 6.9 or 13.9 micromol/g body weight), D-fructose (6.9 micromol/g), both D-glucose and D-fructose (1.7 or 3.5 micromol/g of each hexose) or sucrose (3.7 micromol/g) were administered intragastrically to overnight fasted rats and the plasma concentration of D-glucose, D-fructose and insulin measured over the ensuing 120 minutes. Control experiments were conducted after oral administration of H(2)O or saline.


RESULTS
The administration of D-fructose, given as the free hexose or as sucrose, instead of augmenting the plasma D-glucose concentration evoked by the concomitant administration of D-glucose, tended both to improve the insulin response of the pancreatic B-cell and to minimize hyperglycemia, when compared to the results of experiments including the administration of equimolar amounts of D-glucose alone. For instance, the area under the plasma D-glucose curve was comparable in the rats receiving both D-glucose and D-fructose (3.5 micromol/g of each hexose) and the rats receiving only D-glucose (3.5 micromol/g), averaging respectively 836 +/- 32 and 850 +/- 34 mM . min each. Likewise, the paired ratio between the areas under the plasma insulin and D-glucose curves, when corrected for the threshold concentration for the insulinotropic action of the hexose (2.05 +/- 0.10 mM), averaged 44.3 +/- 3.0 nmol/mol in the 16 rats receiving D-fructose alone, sucrose alone or both D-glucose and D-fructose, as compared to 37.7 +/- 2.9 nmol/mol in the 22 rats receiving increasing amounts of D-glucose alone.


CONCLUSIONS
The intake of D-fructose, as the free hexose or as sucrose, favours D-glucose homeostasis. This is likely to be attributable to the reciprocal effects of the aldose and ketose upon their respective phosphorylation by glucokinase in both hepatocytes and insulin-producing pancreatic islet cells.
Laboratory of Experimental Hormonology, Brussels Free University (CP 626), 808 Route de Lennik, B-1070 Brussels, Belgium.
Pablo G
PG
Prieto
Jesus
J
Cancelas
Maria L
ML
Villanueva-Peñacarrillo
Isabel
I
Valverde
Willy J
WJ
Malaisse
D000284:Administration, Oral; D000818:Animals; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005632:Fructose / Q000008:administration & dosage* / Q000378:metabolism* / Q000493:pharmacokinetics; D005947:Glucose / Q000008:administration & dosage* / Q000493:pharmacokinetics; D007328:Insulin / Q000097:blood*; D007441:Intubation, Gastrointestinal; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013395:Sucrose / Q000008:administration & dosage
D001786:Blood Glucose; D007328:Insulin; D005632:Fructose; D013395:Sucrose; D005947:Glucose