Aspirin survival in human blood modulated by the concentration of erythrocytes

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Abstract
In vitro aspirin hydrolysis rates were measured in fresh human whole blood and in its separate components. The half-life of aspirin in whole blood was relatively rapid (mean 22.2 ± 3.9 minutes) and exhibited a significant negative correlation with hematocrit (r = −0.96). Hydrolysis of aspirin in buffer that contained only washed red blood cells (40%) was significantly more rapid (mean half-life 17.5 ± 2.0 minutes) than that in whole blood. When aspirin was incubated in solutions of washed red blood cells that contained human serum albumin in various concentrations, the aspirin half-life was found to vary directly with the concentration of albumin used; at normal levels of albumin, the hydrolysis rate of aspirin approximated that measured in whole blood. The presence of diisopropyl fluorophosphate in low concentrations (0.02–0.05 mM) markedly inhibited the rate of aspirin hydrolysis in washed red blood cells and whole blood. We conclude that enzyme(s) linked to the erythrocyte, probably membrane-bound acetylcholinesterase, control the survival of aspirin in blood.