Rapid modulation of platelet aggregation in plasma by oxygenated sterols

The effect of oxygenated sterols on platelet aggregation induced by thrombin and ADP has been studied. All oxygenated sterols tested with a hydroxyl group on the side chain enhanced thrombin-induced aggregation at 25 microM. In the case of ADP-induced aggregation, however, only 22S-hydroxycholesterol[(22S)-5-cholestene-3 beta,22-diol] enhanced the aggregation, and 22R-hydroxycholesterol[(22R)-5-cholestene-3 beta,22-diol], 24S-hydroxycholesterol[(24S)-5-cholestene-3 beta,24-diol], and 25-hydroxycholesterol[5-cholestene-3 beta,25-diol] inhibited it. These effects were observed within 10 min after the addition of oxygenated sterols to platelet suspensions in plasma.