The Insulin-Induced Increase of Guanosine-3′,5′-Cyclic Monophosphate in Human Platelets Is Mediated by Nitric Oxide

Abstract

To investigate whether the insulin-induced increase of guanosine-3ʹ,5ʹ-cyclic monophosphate (cGMP) in human platelets is mediated by nitric oxide or is influenced by the nitric oxide precursor L-arginine, we measured cGMP in platelet-rich plasma obtained from healthy volunteers incubated for 3 min with human recombinant insulin (0, 240, 480, 960, and 1,920 pmol/l) both with and without 1) a 20-min incubation with the nitric oxide–synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) (50, 70, 100, and 1,000 μmol/l; n = 5 for each dose) and 2) a 20-min incubation with the nitric oxide precursor L-arginine (300 μmol/l; n = 6). In a first set of experiments, insulin induced a dose-dependent cGMP increase, from 9.8 ± 0.8 to 45.6 ± 5.5 pmol/l09 platelets (P = 0.0001); in the presence of 1 mmol/l L-NMMA, this increase was blunted, cGMP being 8.9 ± 1.4 and 11.1 ± 2.2 pmol/l09 platelets at 0 and 1,920 pmol/l insulin, respectively (NS). In the experiments with 70 and 100 μmol/l L-NMMA, the insulin effect on cGMP was inhibited, whereas 50 μmol/l L-NMMA did not blunt this insulin effect. In another set of experiments carried out to investigate the effects of L-arginine, insulin induced a dose-dependent cGMP increase, from 23.6 ± 6.9 to 59.0 ± 12.0 pmol/l09 platelets (P = 0.0001); with L-arginine, basal cGMP values increased to 35.5 ± 6.6 pmol/l09 platelets (P = 0.05), and insulin maintained its ability to enhance dose-dependently cGMP values, which rose to 76.8 ± 19.4 pmol/l09 platelets (P = 0.003). This study carried out in human platelets demonstrates that the cGMP increase induced by insulin, which accounts for the antiaggregating effect of the hormone, is mediated by nitric oxide.