Platelet function is inhibited by nitric oxide liberation during nitroglycerin-induced hypotension anaesthesia

The inhibitory effects of nitroglycerin (NTG) on platelet function and the mechanisms of inhibition have been studied in vitro, but not in vivo. Therefore, we have investigated the effects of NTG on platelet function in eight patients undergoing orthopaedic surgery. Simultaneous measurements of platelet aggregation and change in intracellular calcium concentrations were performed in Fura-2 loaded platelets using thrombin as a stimulator. Intraplatelet concentrations of cyclic 3',5'-guanine monophosphate (cGMP) were measured by radioimmunoassay, and the concentration of nitrite ion was also measured. Continuous i.v. infusion of NTG 4-8 mu g kg(-1) min(-1) significantly inhibited platelet aggregation and the increase in intracellular Ca2+ concentration (first phase, mean 439.9 (SEM 68.7) vs 210.6 (38.7) nmol litre(-1): second phase, 154.4 (19.8) vs 106.7 (18.0) nmol litre(-1)). The concentration of cGMP (from 0.633 (0.098) to 1.764 (0.578) pmol/10(9) platelets) and the concentration of nitrite ion (From 532.6 (17.6) to 724.4 (34.8) nmol litre(-1)) also increased significantly after infusion of NTG. The NTG concentration in plasma was of the order of 10(-8) mot litre-l We have demonstrated that in vivo, NTG increased intraplatelet cGMP concentrations and inhibited platelet function; one mechanism of this effect is likely to be related to nitric oxide liberation from NTG bioconversion.