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 three to four times the islet volume. In pieces of pancreas exposed up t
o 1 h to H-3-glibenclamide, however, its apparent distribution space progre
ssively increased and, even at the min 60 of incubation, did not exceed a t
hird of the wet weight of the pieces. Yet, no significant difference could
be detected between the time course for H-3-glibenclamide uptake by pancrea
tic pieces from either control animals or rats injected with streptozotocin
a few days before the experiments. Likewise, no significant difference in
the paired ratio between the radioactive content of the pancreas and plasma
could be found between the control and diabetic rats when examined 1, 5, o
r 24 h after the IV administration of H-3-glibenclamide. These findings ind
icate that the sulfonylurea does not represent a suitable tool for preferen
tial labeling of the endocrine pancreas in the perspective of its imaging b
y a noninvasive procedure.