Effects of adenosine on ex vivo filtragometry platelet aggregation in relation to plasma levels

The aim of the present study was to investigate the concentration effect of adenosine on unstimulated platelet aggregation in humans. Adenosine infusion was given intravenously to 12 volunteers in the antecubital vein with infusion rates increasing from 20 to 100 micrograms kg-1 min-1. Filtragometry measurements were obtained from the contralateral antecubital vein before and during 100 micrograms kg-1 min-1 or during maximal tolerable infusion rate. In another set of experiments with 10 volunteers, basal filtragometry measurements were obtained before and after infusion of various concentrations of adenosine into the filtragometer test unit. With intravenous infusion aggregation time tended to increase from 333 +/- 42 to 418 +/- 8 s (mean +/- SEM) and increased the venous plasma adenosine concentration from 0.42 +/- 0.09 microM to 1.52 +/- 0.38 microM. Adenosine infusion into the filtragometer tubing system dose-dependently inhibited aggregation (P < 0.05). Adenosine was rapidly eliminated with a half-life of adenosine in the filtragometry tubing system calculated to be about 6 s. These data extend our knowledge from an in vitro to an ex vivo situation that adenosine dose-dependently has a platelet antiaggregatory effect.