INTRAVENOUS COCAINE INDUCES PLATELET ACTIVATION IN THE CONSCIOUS DOG

Background Cocaine consumption has been associated with thrombosis of coronary and peripheral arteries. Since cocaine has been found to induce platelet activation in vitro, we sought to establish whether cocaine induced platelet activation in vivo. Methods and Results Chronically instrumented, conscious dogs were infused with cocaine (1 mg/kg), norepinephrine (0.2 to 0.4 mg/kg), or saline intravenously over 1 minute. Activated canine platelets were identified in whole blood collected from an indwelling aortic catheter by flow cytometric detection of the binding of a monoclonal antibody directed against the activation-dependent antigen P-selectin. Infusion of cocaine resulted in an elevation of mean arterial pressure (91+/-3 to 128+/-7 mm Hg [P<.001]) and heart rate (87+/-9 to 125+/-11 beats per minute [P<.01]). A similar change (P=NS) in mean arterial pressure followed norepinephrine infusion (100+/-5 to 137+/-13 mm Hg [P<.04]), whereas saline Infusion had no effect. Cocaine resulted in a substantial but delayed increase in platelet P-selectin expression (14+/-7% [P<.08], 31+/-12% [P<.04], and 55+/-22% [P<.04] at 17, 22, and 27 minutes after drug infusion, respectively). The magnitude of this increase was similar to that found in blood treated ex vivo with the agonists ADP or PAF (23+/-7% and 53+/-15%, respectively). No significant increase in P-selectin expression was detected in the blood of animals that received norepinephrine or saline. Serum cocaine concentrations were highest immediately after infusion (538+/-55 ng/mL at 2 minutes) but declined rapidly (185+/-22 and 110+/-25 ng/mL at 17 and 32 minutes after infusion); in contrast, the increase in benzoylecgonine concentrations was delayed (from <25 ng/mL in all but one animal [34 ng/mL] at 2 minutes to 46+/-4 and 71+/-11 ng/mL at 17 and 32 minutes, respectively, after infusion). Conclusions Intravenous cocaine induces activation of individual circulating platelets; this effect is not reproduced by infusion of norepinephrine at doses sufficient to exert similar hemodynamic effects. The delay in detection of activated platelets after treatment with cocaine may result from the adhesion and subsequent detachment of activated platelets; alternatively, cocaine metabolites, rather than the drug itself, may induce platelet activation.