Glucose stimulates the expression and activities of nitric oxide synthases in incubated rat islets: an effect counteracted by GLP-1 through the cyclic AMP/PKA pathway.
We have examined the expression and activity of inducible nitric oxide synthase (iNOS) and the activity of neuronal constitutive NOS (ncNOS) in isolated rat pancreatic islets, stimulated by a "hyperglycaemic" concentration of glucose, and whether the NOS activities could be modulated by activation of the cyclic AMP/protein kinase A (cyclic AMP/PKA) system in relation to the insulin secretory process. Here, we show that glucose stimulation (20 mmol/l) induces iNOS and increases ncNOS activity. No iNOS is detectable at basal glucose levels (3.3 mmol/l). The addition of glucagon-like-peptide 1 (GLP-1) or dibutyryl-cAMP to islets incubated with 20 mmol/l glucose results in a marked suppression of iNOS expression and activity, a reduction in ncNOS activity and increased insulin release. The GLP-1-induced suppression of glucose-stimulated iNOS activity and expression and its stimulation of insulin release is, at least in part, PKA dependent, since the PKA inhibitor H-89 reverses the effects of GLP-1. These observations have been confirmed by confocal microscopy showing the glucose-stimulated expression of iNOS, its suppression by GLP-1 and its reversion by H-89 in beta-cells. We have also found that the NO scavenger cPTIO and the NOS inhibitor L-NAME potentiate the insulin response to glucose, again suggesting that NO is a negative modulator of glucose-stimulated insulin release. We conclude that the induction of iNOS and the increase in ncNOS activity caused by glucose in rat islets is suppressed by the cyclic AMP/PKA system. The inhibition of iNOS expression by the GLP-1/cyclic AMP/PKA pathway might possibly be of therapeutic potential in NO-mediated beta-cell dysfunction and destruction.
Jimenez-Feltstrom
Javier
J
Department of Pharmacology, Institute of Physiological Sciences, University of Lund, 221 84 Lund, Sweden.
Lundquist
Ingmar
I
Salehi
Albert
A
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology*; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004357:Drug Synergism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D042282:Microdissection; D018613:Microscopy, Confocal; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D010446:Peptide Fragments / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011498:Protein Precursors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides / Q000494:pharmacology
D003497:Cyclic N-Oxides; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D007093:Imidazoles; D007328:Insulin; D007546:Isoquinolines; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D011498:Protein Precursors; D013449:Sulfonamides; C079391:2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; D003994:Bucladesine; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D019331:NG-Nitroarginine Methyl Ester