Labeling of pancreatic glycogen by D-[U-C-14]glucose in hyperglycemic rats

Under conditions of sustained hyperglycemia, glycogen accumulates in pancre atic islets, but not so in acinar pancreatic cells. We investigated whether advantage could be taken of such a situation in the perspective of the non invasive imaging of the endocrine pancreas. Control rats or animals injecte d with streptozotocin (STZ) were infused with solutions of D-glucose mixed with a tracer amount of D-[U-C-14]glucose, and the radioactive glycogen con tent of both liver and pancreas was then measured. After 48 h of infusion, the radioactive glycogen content of the pancreas was 30 times lower in STZ rats than in control animals, coinciding with a 50 times lower insulin cont ent. In the control rats, a sizable labeling of pancreatic glycogen was als o recorded when D-[U-C-14]glucose was infused for only the last 4 h of unla beled D-glucose infusion; such a labeling was not decreased when the animal s were further infused for 1 h with only the unlabeled hexose. Moreover, a pronounced difference in the pancreatic gland and blood radioactive content of control rats was still observed when the hyperglycemic animals were kil led only 40 min after the iv injection of D-[U-C-14]glucose. In STZ rats tr ansplanted with islets and later infused with D-[U-C-14]glucose, the total radioactive content and radioactive glycogen content were both much higher in the transplanted islets than in the pancreatic gland. These results allo w one to define the conditions under which the administration of either 2-d eoxy-2-[F-18]fluoro-D-glucose or C-11-labeled D-glucose could conceivably b e used to favor the selective labeling of the endocrine, as distinct from e xocrine, pancreas.