Abstract
The effect of a calcium antagonist nicardipine on hemodynamics in collateral circulation through the the circle of Willis after the occlusion of common carotid arteries (CCAs) was studied.
Materials and methods : The experiments were performed on 10 adult cats anesthetized with alpha-chloralose and urethane. After partial craniotomy, pial arterial blood pressure (PAP) was continuously recorded by a micropressure recording device (Model 900), and cerebral blood flow (CBF) was measured by hydrogen clearance method. In 6 cats systemic arterial blood pressure (SAP), PAP, and CBF were measured in steady state, and after unilateral CCA and bilateral CCAs occlusion. After recirculation of CCAs, the same procedures were done with continuous intravenous infusion of nicardipine (2 μg/kg/min). In 4 cats the reproducibilities of SAP, PAP, and CBF in repeated occlusions of CCAs were studied.
Results : Repeated occlusions resulted no significant change in SAP, PAP and CBF. Despite significant reduction of SAP and PAP after nicardipine administration, a significant increase of CBF was observed in the steady state. The reduction of PAP was greater than that of SAP. Even after the occlusions of unilateral or bilateral CCAs, CBF was increased with a reduction of PAP during infusion of nicardipine. The reduction of small arterial resistance (PAP/CBF) was significantly greater than that of large arterial resistance ((SAP-PAP) /CBF) during infusion of nicardipine. Moreover, nicardipine decreased the resistance of the anterior part of the circle of Willis more markedly than that of the posterior part, although both reductions were significant as compared with control group.
Conclusion : These results indicate that the cerebral artery has a regional difference in reactivity to this calcium antagonist. This drug may be clinically effective even in conditions of low cerebral perfusion pressure induced by carotid occlusion in man.
