ObjectiveTo measure the correlation of plasma adenosine levels with platelet activation in women with preeclampsia.MethodsPlasma adenosine concentration and expression of P-selectin, a marker for platelet activation, were measured in 18 normal pregnant women and 18 preeclamptic women. The effect of 8-sulfophenyltheophylline, an adenosine receptor blocker, on expression of P-selectin on platelets also was measured.ResultsPlasma adenosine level averaged 0.77 ± 0.11 μM (standard error of the mean [SEM]) in women with preeclampsia, significantly higher than the mean level of 0.47 ± 0.08 μM in women with normal pregnancies (P< .05). Expression of P-selectin on platelets averaged 7.8 ± 1.2% in women with preeclampsia, also significantly higher than the mean level of 4.7 ± 0.7% in normal pregnancy (P< .05). Adenosine receptor blockade significantly increased expression of P-selectin on platelets in women with preeclampsia by 26% (P< .05), which was significantly higher than the 13% increase of activation in those with normal pregnancies (P< .05).ConclusionAdenosine is an established platelet activation suppressor. Increased plasma levels of adenosine in preeclampsia might partially compensate and tend to prevent further excessive platelet activation in women with preeclampsia.