Circulation, Vol 66, 1299-1307, Copyright © 1982 by American Heart Association
RI Levin, BB Weksler and EA Jaffe
Sodium nitroprusside (NP) is a potent vasodilator that also inhibits
platelet aggregation. To test the hypothesis that NP causes both of these
effects by altering the balance between prostacyclin (PGI2) produced by
endothelial cells and thromboxane A2 (TXA2) produced by platelets, we
incubated each of these cell types with NP for 5 minutes and assayed the
PGI2 and TXA2 produced. NP at pharmacologically achieved doses (0.01--30
micrograms/ml) inhibited platelet aggregation and resultant TXA2 synthesis
in a dose- and time-dependent manner (p less than 0.001). The inhibition
was not dependent on cAMP production, external calcium concentration, or
suppression of TXA2 synthesis. NP did not alter the production of PGI2 by
cultured human endothelial cells as measured by radioimmunoassay for
6-Keto-PGF1 alpha, the stable hydrolysis product of PGI2. However,
supernates of NP-treated endothelial cells containing low, noninhibitory
concentrations of NP unexpectedly inhibited platelet aggregation. This
inhibition of platelet aggregation was due to synergy between PGI2 (0.1--3
nM) and NP (p interaction less than 0.03). The synergistic inhibition by NP
and PGI2 of platelet aggregation and TXA2 synthesis in vivo may explain
some of the beneficial actions of NP in the treatment of hypertension and
congestive heart failure.
ARTICLES
The interaction of sodium nitroprusside with human endothelial cells and platelets: nitroprusside and prostacyclin synergistically inhibit platelet function
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