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1 Clínica Puerta de Hierro and Department of Physiology, Universidad Autónoma de Madrid, 28035 Madrid, Spain; and 2 Amylin Pharmaceuticals Inc., San Diego, California 92121
Amylin, a peptide hormone from
pancreatic
-cells, is reported to inhibit insulin secretion in vitro
and in vivo and to inhibit nutrient-stimulated glucagon secretion in
vivo. However, it has been reported not to affect arginine-stimulated
glucagon secretion in vitro. To resolve if the latter resulted from
inactive peptide (a problem in the early literature), those experiments
were repeated here with well-characterized peptide and found to be
valid. In isolated perfused rat pancreas preparations, coperfusion with 1 nM amylin had no effect on arginine-, carbachol-, or vasoactive intestinal peptide-stimulated glucagon secretion. Amylin also had no
effect on glucagon output stimulated by decreasing glucose concentration from 11 to 3.2 mM or on glucagon suppression caused by
increasing glucose from 3.2 to 7 mM. Amylin at 100 nM had no effect in
isolated islets in which glucagon secretion was stimulated by exposure
to 10 mM arginine, even though glucagon secretion in the same
preparation was inhibited by somatostatin. In anesthetized rats, amylin
coinfusion had no effect on glucagon secretion stimulated by
insulin-induced hypoglycemia. To reconcile reports of glucagon inhibition with the absence of effect in the experiments just described, anesthetized rats coinfused with rat amylin or with saline
were exposed sequentially to intravenous L-arginine (during a euglycemic clamp) and then to hypoglycemia. Amylin inhibited arginine-induced, but not hypoglycemia-induced, glucagon secretion in
the same animal. In conclusion, we newly identify a selective glucagonostatic effect of amylin that appears to be extrinsic to the
isolated pancreas and may be centrally mediated.
rat pancreas; isolated islets; in vivo; amylin; glucagon
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