Pancreatic fate of C-14-labelled hexoses

In order to assess the respective contribution of the exocrine and endocrin e moieties of the pancreas to the overall net uptake of selected monosaccha rides by the pancreatic gland, the apparent distribution space of L-[1-C-14 ]glucose, 3-O-[C-14-methyl]-D-glucose, D-[U-C-14]glucose, D-[U-C-14]mannose and D-[U-C-14]fructose was measured in pieces of pancreas obtained from ei ther control rats or animals injected with streptozotocin. Although the tim e course for the uptake of 3-O-[C-14-methyl]-D-glucose, D-[U-C-14]glucose, D-[U-C-14]mannose and D-[U-C-14]fructose was much slower in the pieces of p ancreas than that previously documented in isolated pancreatic islets, no s ignificant difference could, as a rule, be detected between the results obt ained in pancreatic pieces of control and streptozotocin rats. A comparable situation prevailed in the pancreas of animals examined 3 min after the in travenous injection of 3-O-[C-14-methyl]-D-glucose. D-Glucose inhibited the uptake of 3-O-[C-14-methyl]-D-glucose and that of D-[U-C-14]fructose. Like wise, 3-O-methyl-D-glucose inhibited the uptake of D-[U-C-14]glucose. Cytoc halasin B (20 muM) also inhibited the uptake of 3-O-[C-14-methyl]-D-glucose and D-[U-C-14]glucose, but not that of D-[U-C-14]fructose. D-Mannoheptulos e hexaacetate, but not the unesterified heptose, inhibited the metabolism o f tritiated and C-14-labelled D-glucose, as well as the net uptake of D-[U- C-14]glucose and D-[U-C-14]mannose and, to a lesser extent, that of D-[U-C- 14]fructose. These findings indicate that despite marked differences betwee n endocrine and exocrine pancreatic cells in terms of both the time course for the uptake of several hexoses and the inhibition of their phosphorylati on by D-mannoheptulose, little or no preferential labelling of the endocrin e moiety of the pancreas by the C-14-labelled hexoses is observed, at least when judged from their distribution space in pancreatic pieces or the whol e pancreatic gland. Nevertheless, the findings made with D-mannoheptulose a nd its hexaacetate eater raise the view that this heptose could conceivably be used to achieve a sizeable preferential labelling of the endocrine panc reas under the present experimental conditions. Copyright (C) 2000 John Wil ey & Sons, Ltd.