Antiplatelet effects of sodium nitroprusside in flowing human blood: Studies under normoxic and hypoxic conditions

We explored the ability of sodium nitroprusside to modify adhesive and cohe sive function of platelets in flowing blood, under normoxic and hypoxic con ditions. Aliquots of both untreated and sodium nitroprusside-treated blood were prepared for studies of: (1) platelet aggregation in plasma; (2) eryth rocyte deformability; (3) platelet interaction with damaged subendothelium, by using a well-defined perfusion system; and (4) blood gasometry in the p erfused samples. Results showed that sodium nitroprusside-treated blood alw ays showed a totally inhibited arachidonic acid-induced platelet aggregatio n in plasma, as well as significantly increased erythrocyte deformability ( 0.44 +/- 0.09 up to 0.66 +/- 0.05; p < 0.05). However, treatment with sodiu m nitroprusside did not modify the pattern of platelet interaction with sub endothelium (percentage of contact, adhesion, thrombus, and covered surface ) with respect to untreated blood, under any of the shear rates used (300, 800, and 1800 seconds(-1)), although it significantly reduced the height of thrombi (9.8 +/- 0.4 vs. 8.3 +/- 0.4 mu m; p < 0.05). Hypoxic conditions d id not have a noticeable effect in modifying antiplatelet effects of sodium nitroprusside. Additionally, the presence of sodium nitroprusside impaired the normal oxygenation of the blood during perfusion. pO(2) in control unt reated samples rose from 40.3 +/- 5.0 mm Hg perfusions to 100.4 +/- 12.5 mm Hg but remained at 66.3 +/- 6.3 mm Hg in sodium nitroprusside-treated bloo d (p < 0.05). Our results did not show a significant effect of sodium nitro prusside in the modulation of platelet interaction with subendothelium. The marginal reduction in the thrombi height could be related to rheological i nterference of increased erythrocyte deformability. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.