Influence of nitric oxide synthase inhibition, nitric oxide and hydroperoxide on insulin release induced by various secretagogues

Abstract

1 Recent studies have suggested that the generation of nitric oxide (NO) and hydrogen peroxide (H202) by islet NO synthase and monoamine oxidase, respectively, may have a regulatory influence on insulin secretory processes. We have investigated the pattern of insulin release from isolated islets of Langerhans in the presence of various pharmacological agents known to perturb the intracellular levels of NO and the oxidation state of SH-groups.2 The NO synthase inhibitor, N0-nitro-L-arginine methyl ester (L-NAME) dose-dependently increased L-arginine-induced insulin release. D-Arginine did not influence L-arginine-induced insulin secretion.However, D-NAME which reportedly has no inhibitory action on NO synthase, modestly increased L-arginine-induced insulin release, but was less effective than L-NAME. High concentrations (10 mM) of D-arginine as well as L-NAME and D-NAME could enhance basal insulin release. 3 The intracellular NO donor, hydroxylamine, dose-dependently inhibited insulin secretion induced by L-arginine and L-arginine + L-NAME.4 Glucose-induced insulin release was increased by NO synthase inhibition (L-NAME) and inhibited by the intracellular NO donor, hydroxylamine. Sydnonimine-I (SIN-1), an extracellular donor of NO and superoxide, induced a modest suppression of glucose-stimulated insulin release. SIN-1 did not influence insulin secretion induced by L-arginine or the adenylate cyclase activator, forskolin. L-arginine or tert-butylhydroperoxide at 3 or 300 gM but was markedly increased (14 fold) by a high hydroxylamine concentration (300 gM). In contrast, islet adenosine 3':5'-cyclic monophosphate (cyclic AMP) content was increased (3 fold) by L-arginine (10 mM) and (2 fold) by tert-butylhydroperoxide (300 gM).7 Our results strongly suggest that NO is a negative modulator of insulin release induced by the nutrient secretagogues L-arginine and glucose. This effect is probably not mediated to any major extent by the guanylate cyclase-cyclic GMP system but may rather be exerted by the S-nitrosylation of critical thiol groups involved in the secretory process. Similarly the inhibitory effect of tert-butylhydroperoxide is likely to be elicited through affecting critical thiol groups. The mechanism underlying the secretionpromoting action of tert-butylhydroperoxide on IBMX-induced insulin release is probably linked to intracellular Ca2'-perturbations affecting exocytosis.8 Taken together with previous data the present results suggest that islet production of low physiological levels of free radicals such as NO and H202 may serve as important modulators of insulin secretory processes.

Expression of islet inducible nitric oxide synthase and inhibition of glucose-stimulated insulin release after long-term lipid infusion in the rat is counteracted by PACAP27

“…The mechanisms of action of NO to restrain glucose-stimulated insulin release are still unclear, although reduction of oxidative metabolism of glucose and thereby reduced ATP generation might play a role in the presence of high concentrations of NO (5,6,23). We have previously hypothesized that S-nitrosylation of the glutathione system and/or important regulatory proteins at distal sites in the secretory process are possible targets (1,16,27,38). In fact, a new proteomic approach in brain tissue has revealed a wide range of metabolic and signaling proteins that might serve as Means Ϯ SE for 6 -8 batches of islets/group, isolated from 6 rats, are shown.…”

“…Before assay 500 l of H 2O was added, and the samples were sonicated (3 ϫ 5 s) followed by centrifugation (1,100 g) for 15 min. As previously described (27,35), the supernatants were then collected and extracted with water-saturated diethyl ether (4 ϫ 2 ml). The aqueous phase was removed and freeze-dried, using a Lyovac GT 2 freeze dryer.…”

Exogenous Nitric Oxide and Endogenous Glucose-Stimulated β-Cell Nitric Oxide Augment Insulin Release

“…NOS inhibition has been reported to produce an inhibitory effect (5,(13)(14)(15), a stimulatory effect (6,9,16 -18), and no effect at all (19,20) on insulin release. Similarly, exogenously applied NO has been reported to exert a stimulatory (5,13,14,21,22) and an inhibitory effect (6,18,(23)(24)(25)(26)(27) on insulin release. These discrepant data may be the result of variations in the specifics of the experimental conditions, including differences in the agents used (e.g., NOS substrate, NOS inhibitors, NO donors), the concentration of these agents, whether other stimulatory pathways were activated concurrently (e.g., with glucose), the experimental model used (e.g., ␤-cell line, islets, pancreas), and the species.…”

The early phase of glucose-stimulated insulin secretion requires nitric oxide

“…Some investigations provided evidence that NO, presumably produced by a calcium/calmodulin-dependent constitutive NO synthase (NOS), participates in the signal transduction pathway mediating insulin secretion [6], and that L-arginine-derived NO mediates insulin secretion via stimulation of guanylate cyclase and cGMP formation [7]. Others found no evidence for endogenously produced NO being involved in the initiation of secretagogue-induced insulin release [8] or reported that L-arginine-derived NO may even inhibit insulin release [9].Recently, Willmott et al [10] showed that beta cells preloaded with tryptamine, which accumulates in insulin-containing granules and is co-secreted with insulin, respond to NO by mobilizing Ca 2+ from the endoplasmic reticulum accompanied by a release of tryptamine from the cells. These data corroborate our previous finding that exogenously added NO Diabetologia (1998) Summary Nitric oxide (nitrogen monoxide, NO) acts as a signal transducer in a variety of cells.…”

“…Some investigations provided evidence that NO, presumably produced by a calcium/calmodulin-dependent constitutive NO synthase (NOS), participates in the signal transduction pathway mediating insulin secretion [6], and that L-arginine-derived NO mediates insulin secretion via stimulation of guanylate cyclase and cGMP formation [7]. Others found no evidence for endogenously produced NO being involved in the initiation of secretagogue-induced insulin release [8] or reported that L-arginine-derived NO may even inhibit insulin release [9].…”