THE INSULIN-INDUCED INCREASE OF GUANOSINE-3',5'-CYCLIC MONOPHOSPHATE IN HUMAN PLATELETS IS MEDIATED BY NITRIC-OXIDE

To investigate whether the insulin-induced increase of guanosine-3',5' -cyclic monophosphate (cGMP) in human platelets is mediated by nitric oxide or is influenced by the nitric oxide precursor L-arginine, we me asured cGMP in platelet-rich plasma obtained from healthy volunteers i ncubated for 3 min with human recombinant insulin (0, 240, 480, 960, a nd 1,920 pmol/l) both with and without 1) a 20-min incubation with the nitric oxide-synthase inhibitor N-G-monomethyl-L-arginine (L-NMMA) (5 0, 70, 100, and 1,000 mu mol/l; n = 5 for each dose) and 2) a 20-min i ncubation with the nitric oxide precursor L-arginine (300 mu mol/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/10(9) platelets ( P = 0.0001); in the presence of 1 mmol/l L-NR IMA, this increase was b lunted, cGMP being 8.9 +/- 1.4 and 11.1 +/- 2.2 pmol/10(9) platelets a t 0 and 1,920 pmol/l insulin, respectively (NS). In the experiments wi th 70 and 100 mu mol/l L-NMMA, the insulin effect on cGMP was inhibite d, whereas 50 mu mol/l L-NMMA did not blunt this insulin effect. In an other set of experiments carried out to investigate the effects of L-a rginine, insulin induced a dose-dependent cGMP increase, from 23.6 +/- 6.9 to 59.0 +/- 12.0 pmol/10(9) platelets (P = 0.0001); with L-argini ne, basal cGMP values increased to 35.5 +/- 6.6 pmol/10(9) platelets ( P = 0.05), and insulin maintained its ability to enhance dose-dependen tly cGMP values, which rose to 76.8 +/- 19.4 pmol/10(9) platelets (P = 0.003). This study carried out in human platelets demonstrates that t he cGMP increase induced by insulin, which accounts for the antiaggreg ating effect of the hormone, is mediated by nitric oxide.