AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 5 599-G606, Copyright © 1985 by American Physiological Society
Capillary orientation of rat pancreatic D-cell processes: evidence for endocrine release of somatostatin
G. Aponte, D. Gross and T. Yamada
We examined the ultrastructure of somatostatin-containing pancreatic
D-cells in the rat in order to shed light on the function and mode of
action of somatostatin in the pancreas. D-cells were first identified by
indirect immunocytochemistry with the peroxidase-antiperoxidase technique
on semithin (1-micron) sections of 2% glutaraldehyde-1.7%
paraformaldehyde-fixed tissue from the tail of the pancreas. Fine
ultrastructure of the positively identified D-cells was examined in
adjacent sections (0.08 micron) by electron microscopy. D-cells
characteristically exhibited long cytoplasmic projections that extended to
capillaries. Each cell was divided arbitrarily into three zones of roughly
equal size, nuclear, central, and capillary, and distribution of secretory
granules into each zone was quantified. In unstimulated cells, secretory
granules were dispersed throughout the D-cell. In sections obtained from
rats stimulated to secrete somatostatin by infusion of 20 mM glucose-5 mM
theophylline-20 mM L-arginine HCl, 75 +/- 4% of the D-cell granules was
polarized to the capillary end of the cell, while only 54 +/- 2% was is
this region in unstimulated rats (P less than 0.05). These studies suggest
that pancreatic somatostatin is released into islet capillaries.
