Effect of Dipyridamole on Spontaneous Platelet Aggregation in Whole Blood Decreases with the Time After Venepuncture: Evidence for the Role of ADP

Abstract

SummarySpontaneous platelet aggregation (SPA) was studied in human whole blood at 3, 5, 10, 20, 30, 40 and 60 minutes after venepuncture. Using a whole blood platelet counter, SPA was quantified by measuring the fall in single platelet count upon rollermixing aliquots of citrated blood at 37° C. The extent of SPA increased with the time after venepuncture, with a correlation coefficient of 0.819. The inhibitory effect of dipyridamole (Dipy) on SPA was studied: (a) 10 μM at each time interval; (b) 0.5-100 μM at 3 and 30 minutes and (c) 15 μM in combination with 100 μM adenosine, 8 μM 2-chloroadenosine (2ClAd, an ADP receptor blocker) and 50 μM aspirin. There was a rapid decrease in the inhibitory effect of Dipy with the time after venepuncture; the correlation coefficient was -0.533. At all the concentrations studied, Dipy was more effective at 3 minutes than at 30 minutes after venepuncture. A combination of Dipy with adenosine, 2ClAd or aspirin was a more effective inhibitor of SPA than either drug alone. However, when 15 μM Dipy and 10 μM Ad were added together, the inhibitory effect of Dipy was not increased significantly, suggesting that Dipy inhibits platelet aggregation independent of Ad. The increase in SPA with the time after venepuncture was abolished when blood was taken directly into the anticoagulant containing 5 μM 2ClAd. It is suggested that ADP released from the red blood cells is responsible for the increased platelet aggregability with the time after venepuncture and makes a serious contribution to the artifacts of in vitro platelet function studies.

Recovery of in vitro functional activity of platelet concentrates stored at 4 ° C and treated with second‐messenger effectors

“…Dipyridamole was introduced for its ability to inhibit cyclic AMP phosphodiesterase activity and thus to contribute to the accumulation of cyclic AMP within platelets. 42 Another pathway of platelet activation is the arachidonic acid cascade. The generation of arachidonic acid is inhibited by quinacrine, a phospholipase A, inhibitor, which blocks the breakdown of the lipid serving as the source for the arachidonic acid synthesis?'…”

Cell-Free and Erythrocytic S -Nitrosohemoglobin Inhibits Human Platelet Aggregation

“…22 RBCs are also rich sources of ADP, the spontaneous and/or evoked release of which has powerful platelet-activating effects in vitro. 23,24 Likewise, RBCs contain hemoglobin, which readily scavenges EDRF and NO. Thus, not surprisingly, RBCs have been shown to reverse EDRF-and NO-induced inhibition of intravascular platelet aggregation.…”

Dipyridamole Potentiates Platelet Inhibition by Nitric Oxide

“…Such an interaction could form another explanation for the elusive anti-aggregating activity of dipyridamole, since NO is highly labile (half life of seconds) and is avidly trapped by Correspondence to: Dr. Hidde Bult, University of Antwerp (UIA), Division of Pharmacology, B-2610 Wilrijk, Belgium haemoglobin, and it is unlikely to reveal anti-platelet effects once platelets have been removed from the circulation. Parts of the results have been presented at international symposia on the Biology of the Vascular Endothelial Cell (Toronto, July [26][27][28][29][30]1988) and on Endothelium Derived Vasoactive Factors (Philadel phia, May 1-3, 1989) (14).…”