23 January 1997, Volume 120, Issue 3, Pages 495 – 501

Article

Mechanisms involved in the effect of nitric oxide synthase inhibition on L-arginine-induced insulin secretion R. Gross1,4, M. Roye1, M. Manteghetti1, C. Broca1,2, D. Hillaire-Buys2, P. Masiello3 & G. Ribes1 1UMR 9921 du CNRS and     2Laboratoire de Pharmacologie (UPRES EA 1677), Faculté de Médecine, Institut de Biologie, Boulevard Henri IV, 34060 Montpellier Cedex 01, France, and     3Istituto di Patologia Generale, Università di Pisa, Italy     4Author for correspondence

Keywords

Insulin secretion;   glucose;   L-arginine;   nitric oxide synthase inhibitor;   N-nitro-L-arginine methyl ester;   L-citrulline;   NG-hydroxy-L-arginine;   sodium nitroprusside

Abstract

1   A constitutive nitric oxide synthase (NOSc) pathway negatively controls L-arginine-stimulated insulin release by pancreatic cells. We investigated the effect of glucose on this mechanism and whether it could be accounted for by nitric oxide production. 2   NOSc was inhibited by N-nitro-L-arginine methyl ester (L-NAME), and sodium nitroprusside (SNP) was used as a palliative NO donor to test whether the effects of L-NAME resulted from decreased NO production. 3   In the rat isolated perfused pancreas, L-NAME (5 mM) strongly potentiated L-arginine (5 mM)-induced insulin secretion at 5 mM glucose, but L-arginine and L-NAME exerted only additive effects at 8.3 mM glucose. At 11 mM glucose, L-NAME significantly inhibited L-arginine-induced insulin secretion. Similar data were obtained in rat isolated islets. 4   At high concentrations (3 and 300 µM), SNP increased the potentiation of arginine-induced insulin output by L-NAME, but not at lower concentrations (3 or 30 nM). 5   L-Arginine (5 mM) and L-ornithine (5 mM) in the presence of 5 mM glucose induced monophasic cell responses which were both significantly reduced by SNP at 3 nM but not at 30 nM; in contrast, the L-ornithine effect was significantly increased by SNP at 3 µM. 6   Simultaneous treatment with L-ornithine and L-arginine provoked a biphasic insulin response. 7   At 5 mM glucose, L-NAME (5 mM) did not affect the L-ornithine secretory effect, but the amino acid strongly potentiated the alteration by L-NAME of L-arginine-induced insulin secretion. 8   L-Citrulline (5 mM) significantly reduced the second phase of the insulin response to L-NAME (5 mM)+L-arginine (5 mM) and to L-NAME+L-arginine+SNP 3 µM. 9   The intermediate in NO biosynthesis, NG-hydroxy-L-arginine (150 – 300 µM) strongly counteracted the potentiation by L-NAME of the secretory effect of L-arginine at 5 mM glucose. 10   We conclude that the potentiation of L-arginine-induced insulin secretion resulting from the blockade of NOSc activity in the presence of a basal glucose concentration (1) is strongly modulated by higher glucose concentrations, (2) is not due to decreased NO production but (3) is probably accounted for by decreased levels of NG-hydroxy-L-arginine or L-citrulline, resulting in the attenuation of an inhibitory effect on arginase activity.

Received 25 July, 96; Revised 9 October, 96; Accepted 18 October, 96

^© Macmillan Publishers Ltd 1997