Protection against cyclosporine-induced impairment of renal microcirculation by verapamil in mice.

Fluorescence microscopy was used to examine the effect of cyclosporine (CsA) infusion on renal subcapsular (cortical) blood flow in 53 living mice, using FITC-dextran (MW: 156,000) as a fluorescent marker. CsA (8-19 mg/kg body weight) given i.v. for 1 min induced complete inhibition of blood flow. A complete standstill of flow was also obtained during a continuous infusion with a rate of 0.8-2 mg/kg/min. With lower infusion rates (0.15-0.23 mg/kg/min), blood flow was partially impaired. In all experiments, the decrease in flow occurred after a 15-25 min delay, suggesting a CsA metabolite or exhaustion of a protective mechanism as the causative agent. Pretreatment with an alpha-blocking agent, phentolamine (1.0 mg/kg), did not prevent the CsA-induced inhibition of blood flow. In contrast, pretreatment with a calcium antagonist, verapamil (0.3-0.4 mg/kg), prevented the impairment of blood flow at low (0.15-0.23 mg/kg/min), and partially at higher (0.8-2.4 mg/kg/min) rates of CsA infusion. Clinical studies are warranted to explore the role of calcium antagonists in the prevention of posttransplant acute cyclosporine-induced nephrotoxicity.