Effects of cocaine on carotid vascular reactivity in swine after balloon vascular injury.

BACKGROUND AND PURPOSE The use of cocaine has been associated with stroke. To evaluate carotid vasospasm as a potential mechanism of cocaine-induced stroke, we studied 12 swine immediately and 10 weeks after angioplasty. METHODS We compared the short- and long-term vasoconstrictor responses of normal and injured arterial segments to nitroglycerin, histamine, and cocaine in vivo by carotid angiography. We also compared the isometric contractile force responses to different vasoactive substances in normal and injured vascular rings in vivo, and we tested the direct action of cocaine on both arterial segments. RESULTS In in vivo studies, immediately after angioplasty, luminal diameter in the control segment decreased by 30% with histamine 30 micrograms/kg and by 23% with cocaine 10 mg/kg (P < .001). In contrast, neither histamine nor cocaine produced vasoconstriction in the angioplasty segment. Thus, a transient loss of vasoconstriction occurred at the angioplasty site. Ten weeks later, histamine 30 micrograms/kg significantly (P < .001) decreased luminal diameter by 34% in the control and by 33% in the angioplasty segment; similarly, cocaine 10 mg/kg significantly (P < .001) decreased luminal diameter by 26% in the control and by 34% in the angioplasty segment. Thus, 10 weeks after angioplasty, the transitory loss of carotid vasoconstriction in response to histamine and cocaine reverted, and a moderate generalized vasoconstriction occurred in both segments without localized vasospasm. In vitro, the maximal isometric tension responses to KCl, acetylcholine, histamine, and phenylephrine were similar in vascular rings from normal and angioplasty segments. The median effective doses to histamine and phenylephrine were similar. In contrast, cocaine in concentrations from 10(-7) to 10(-3) mol/L failed to produce any isometric contraction in vitro. CONCLUSIONS Cocaine in vivo produced a generalized carotid vasoconstriction without evidence of localized vasospasm; since there was no response to cocaine in vitro, the in vivo effect was most likely mediated by neurohumoral factors rather than by a direct action of cocaine on vascular smooth muscle.