THE INFLUENCE OF THE CYCLOSPORINE VEHICLE, CREMOPHOR EL, ON RENAL MICROVASCULAR BLOOD-FLOW IN THE RAT

Cyclosporine nephrotoxicity may be due to glomerular hypoperfusion. Previous experimental and clinical studies have demonstrated a decrease in renal blood flow and an increase in renal vascular resistance. Cremophor EL, which is the vehicle in which CsA is dissolved, is thought to be a factor involved in intrarenal arteriolar vasoconstriction. To determine the relative contributions of the vehicle and CsA to intrarenal arteriolar vasoconstriction, we used in vivo videomicroscopy and Doppler velocimetry to measure changes in renal microvascular blood flow in the rat. A 5-min intravenous infusion of 20 mg/kg of CsA resulted in a 17% mean reduction (P < 0.05) in the diameter of preglomerular interlobular arterioles and an associated 60% reduction (P < 0.05) in microvascular blood flow by 15 min. Cremophor EL/ethanol equivalent caused less vasoconstriction (up to 10%) but resulted in a 42% mean decrease (P < 0.05) in microvascular blood flow, probably secondary to a 38% mean decrease (P < 0.05) in cardiac output and 13% decrease in arterial pressure. We conclude that cremophor EL does contribute to in vivo reduction of preglomerular microvascular blood flow in the rat. This may be particularly important when using this intravenous preparation in the study of CsA nephrotoxicity.