AJP - Endocrinology and Metabolism, Vol 245, Issue 2 114-E120, Copyright © 1983 by American Physiological Society
Effects of gastric inhibitory polypeptide on leucine- and arginine-stimulated insulin release
E. L. Mazzaferri, L. Ciofalo, L. A. Waters, G. H. Starich, J. C. Groshong and L. DePalma
Insulin release stimulated by single amino acids, with and without gastric
inhibitory polypeptide (GIP), was studied in vivo in anesthetized rats and
in vitro in collagenase-digested isolated rat pancreatic islets. Insulin
release in vivo during a 15-min intravenous infusion of leucine (0.97 mM)
or arginine (0.97 mM) with GIP (17 ng/min) was greater than with infusion
of either amino acid or GIP alone. Serum immunoreactive GIP was in the
physiological range, and serum glucose showed no significant change in
these studies. In contrast, insulin release did not occur with valine
infused alone or with GIP. Insulin release in vitro by isolated islets was
greater during a 45-min incubation period with leucine (5-20 mM) or
arginine (20 mM) plus GIP (10 ng to 10 micrograms/ml) than with either
amino acid alone. This effect that occurred in the absence of glucose could
not be demonstrated with low concentrations of leucine (1.5 mM) or with 20
mM valine. In vitro insulin release during paired perfusion studies of
isolated islets was greater with leucine (20 mM) plus GIP (50 ng/min) than
with leucine alone, and augmentation of insulin release by GIP was
demonstrable in both the early and late phases of insulin release. From
these results it is concluded that insulin release is greater, both in vivo
and in vitro, after leucine or arginine plus GIP than with either amino
acid or GIP alone. This effect appears to be specific for the
insulinotropic amino acids tested, does not appear to be glucose dependent,
and can be demonstrated in both the early and late phases of insulin
release.
