Nitric Oxide (NO)-Platelet Interactions: Inhibition is Independent of the Prostanoid and ADP Pathways

Effects of nitric oxide (NO) on thrombin-induced responses in gel-filtered, [(32)P] Pi-(pre) labeled platelets (GFP) were examined. NO did not alter the levels of (32)P-labeled polyphosphoinositides in unstimulated platelets and did not inhibit the forskolin-induced elevation of [(32)P]PIP (phosphatidylinositol 4-phosphate), which indicates that NO does not concomitantly increase the level of cAMP in resting human platelets. In aspirinated platelets NO inhibited thrombin (0.05 U/ml)-induced formation of [(32)P]phosphatidic acid (PA), secretion of ATP + ADP from the dense granules and secretion of acid glycosidases in a dose-dependent manner. At 0.2 U/ml of thrombin NO still inhibited these responses, although to a lesser degree. In aspirinated platelets in the presence of creatine phosphate/creatine phosphokinase (CP/CPK) to remove secreted ADP, increasing concentrations of NO still produced strong inhibition of [(32)P] PA-formation and secretory responses.