Uptake of tritiated glibenclamide by endocrine and exocrine pancreas

Tritiated glibenclamide binds to specific receptors and is internalized in pancreatic insulin-producing B-cells. We investigated, therefore, whether t ritiated glibenclamide could be used to preferentially label the endocrine, as distinct from exocrine, pancreas. In isolated rat pancreatic islets, th e net uptake of H-3-glibenclamide reached within 30 min of incubation a nea r-equilibrium value, corresponding to an apparent distribution space close to th ree to four times the islet volume. In pieces of pancreas exposed up to 1 h to H-3-glibenclamide, however, its apparent distribution space progr essively increased and, even at the min 60 of incubation, did not exceed a third of the wet weight of the pieces. Yet, no significant difference could be detected between the time course for H-3-glibenclamide uptake by pancre atic pieces from either control animals or rats injected with streptozotoci n a few days before the experiments. Likewise, no significant difference in the paired ratio between the radioactive content of the pancreas and plasm a could be found between the control and diabetic rats when examined 1, 5, or 24 h after the IV administration of H-3-glibenclamide. These findings in dicate that the sulfonylurea does not represent a suitable tool for prefere ntial labeling of the endocrine pancreas in the perspective of its imaging by a noninvasive procedure.