H. Jijakli et Wj. Malaisse, Effect of D-mannoheptulose upon the cationic and secretory responses to alpha-D-glucose pentaacetate in perifused rat pancreatic islets, ENDOCRINE, 10(3), 1999, pp. 219-224
The metabolism of alpha-D-glucose pentaacetate and its positive insulinotro
pic action in isolated rat pancreatic islets are both unexpectedly resistan
t to D-mannoheptulose, as judged from experiments conducted over 90-120 min
incubation. In the present study, the possible effects of the heptose upon
the immediate cationic and secretory response to the ester were investigat
ed in perifused islets prelabeled with either Rb-86 Or Ca-45. At a 10 mM co
ncentration, sufficient to abolish the inhibitory action of unesterified D-
glucose upon 86Rb outflow, D-mannoheptulose failed to suppress the decrease
in Rb-86 outflow and increase in Ca-45 efflux caused by alpha-D-glucose pe
ntaacetate at normal extracellular Ca2+ concentration and also failed to pr
event the decrease in both Ca-45 and insulin release provoked by the ester
in the absence of extracellular Ca2+. The sole obvious effect of the heptos
e was to change the early peak-shaped positive secretory response to alpha-
D-glucose pentaacetate to a transient inhibition of insulin release. This c
hange was observed in islets either deprived of any other exogenous nutrien
t or exposed to L-leucine throughout the experiments. These findings suppor
t the view that the islet functional response to alpha-D-glucose pentaaceta
te is largely resistant to D-mannoheptulose. They also reinforce the concep
t that the insulinotropic action of this and other monosaccharide esters in
volves a dual modality of B-cell activation, linked to both the catabolism
of their carbohydrate moieties and a direct effect of the esters themselves
upon a specific receptor system.