L-Leucine-induced secretion of glucagon and insulin, and the "off-response" to L-leucine in vitro. II. The role of D-glucose
Journal
Endocrinology
Journal Volume
103
Journal Issue
4
Date Issued
1978-10
Author(s)
Abstract
The role of glucose in L-leucine-induced secretion of glucagon and insulin was investigated in the isolated, perfused rat pancreas. In the absence of glucose (or with 2.8 DIM D-glucose) in the perfusion medium, 1) the observed augmentation of the acute phase release of glucagon diminished gradually upon repetitive perfusions of L-leucine; a late phase release was not observed with leucine concentrations up to 10 mM; 2) L-leucine evoked acute phase release of insulin at concentrations of 5 and 10 mM, but not 2 HIM; and 3) the release of insulin which had been observed shortly after the termination of the perfusion of L-leucine (“off-response”in the presence of 5.6 Mm D-glucose failed to occur. In the presence of 16.7 mM D-glucose, 1) acute phase glucagon release was blunted, but there was a marked late phase release with 10 mM L-leucine; 2) L-leucine evoked insulin release even at the low concentration of 2 mM; and 3) the insulin off-response occurred. With 10 mM D-mannoheptulose plus 5.6 mM D-glucose, a small glucagon off-response occurred upon removal of L-leucine; the acute or late phases of leucineinduced insulin release or the insulin off-response failed to occur. With 5.6 mM 3-ortho-D-methylglucose, the insulin off-response to L-leucine occurred in the presence but not in the absence of glucose. With 5 mM fumarate, glutamate, and pyruvate, but without glucose, during L-leucine perfusion, the acute phase of glucagon release occurred and the late phase was inhibited; the insulin off-response failed to occur. The following conclusions were reached. 1) The magnifying effect of glucose deprivation on the secretion of glucagon is evanescent. 2) With an abundance of glucose, the integrity of the mechanisms of synthesis and release of glucagon may be preserved better than in the absence of glucose. 3) Glucose plays a permissive role in L-leucine-induced insulin release and in the insulin off-response to L-leucine. 4) The metabolism of glucose seems to be essential for the insulin off-response to Lleucine to occur. © 1978 by The Endocrine Society.
Type
journal article