The role of nitric oxide (NO) during cyclosporin renal vasoconstriction was evaluated by glomerular hemodynamic and histological changes produced by chronic NO synthesis inhibition and neuronal (nNOS), inducible (iNOS), and endothelial (eNOS) NO synthases mRNA expression in renal cortex and medulla. Uninephrectomized rats treated during 7 days with vehicle (Veh), cyclosporin A (CsA) 30 mg/kg, CsA + nitro-l-arginine methyl ester (l-NAME), and Veh +l-NAME (10 mg/dl) in the drinking water were studied. Increase in arterial pressure and afferent and efferent resistances, as well as decrease in glomerular plasma flow, ultrafiltration coefficient, and single-nephron glomerular filtration rate were significantly greater with CsA +l-NAME than with CsA alone. The increase in afferent resistance was higher with CsA +l-NAME than with Veh +l-NAME. In addition, glomerular thrombosis, proximal tubular vacuolization, and arteriolar thickening were more prominent. In renal cortex, eNOS mRNA expression exhibited a 2.7-fold increase in CsA, whereas, in medulla, nNOS and iNOS expression were lower in CsA than in Veh, while eNOS tended to increase. Our results support the hypothesis that NO synthesis is enhanced at cortical level during CsA nephrotoxicity, counterbalancing predominantly preglomerular vasoconstriction. Higher NO production could be the result of increased eNOS mRNA expression.

Cyclosporin A (CsA)-induced renal vasoconstriction (RV) is attributed to an imbalance in vasoactive factors release. Dexamethasone (Dex) exerts a renal vasodilatory effect by a mechanism not yet characterized. This study evaluates whether the effect of Dex is mediated by NO and whether it prevents CsA-induced RV. Micropuncture studies were performed in six groups of uninephrectomized rats treated for 7 days with the following: vehicle (Veh); Veh + 4 mg/kg dexamethasone (Veh+Dex); 30 mg/kg CsA; CsA+Dex; vehicle + 10 mg/kg nitro-l-arginine methyl ester (Veh+l-NAME); and Veh+Dex+l-NAME. NO synthase (NOS) isoform mRNA levels were evaluated in renal cortex and medulla by semiquantitative RT-PCR analysis in the first four groups. Dex produced renal vasodilation, which was blocked by concomitant l-NAME administration, and the effect of Dex was associated with higher cortical and medullary endothelial NOS (eNOS) and cortical inducible NOS (iNOS) mRNA levels. In the CsA group, Dex prevented RV, restoring glomerular hemodynamics to control values. These changes were associated with further enhancement of eNOS and restoration of medullary iNOS and neuronal NOS (nNOS) expression. We conclude that Dex prevents CsA-induced RV, and its vasodilator effect could be mediated by increased intrarenal generation of NO, secondary to enhanced expression of eNOS and iNOS.

Abstract-Cyclosporine toxicity mainly affects kidney and liver function. We have previously shown that cyclosporine nephrotoxicity alters kidney nitric oxide synthase mRNA pattern of expression. To determine if nitric oxide synthase expression changes are mediated directly by cyclosporine or by secondary hemodynamic alterations induced by cyclosporine, we evaluated if these effects are tissue specific and if nifedipine-induced vasodilation prevents these alterations. Uninephrectomized Wistar rats treated for 7 days with olive oil, cyclosporine (30 mg/kg), nifedipine (3 mg/kg), and nifedipineϩcyclosporine were studied. In vehicle and cyclosporine groups, the gene expression of the neuronal, inducible, and endothelial nitric oxide synthases in cerebellum, heart, intestine, liver, renal cortex, and medulla was evaluated. The administration of cyclosporine was associated with nephrotoxicity and hepatotoxicity, increased endothelial nitric oxide synthase mRNA levels in renal cortex and liver, and a decrease in inducible nitric oxide synthase and neuronal nitric oxide synthase in renal medulla. The mRNA levels of the 3 nitric oxide synthase isoforms were not affected in any other tissue. Nifedipine did not alter nitric oxide synthase expression in the control group but prevented changes associated with cyclosporine. These results suggest that cyclosporine-induced changes in the pattern of expression of the nitric oxide synthases may be secondary to its hemodynamic effects. (Hypertension. 2000;36:642-647.)Key Words: nitric oxide Ⅲ liver Ⅲ hypertension Ⅲ cyclosporine C yclosporine (CsA) is an immunosuppressor drug. Despite its beneficial effects, however, long-term use is frequently associated with hypertension, nephrotoxicity, and hepatotoxicity.Nephrotoxicity is the most common complication associated with CsA therapy. 1 It is characterized by renal vasoconstriction that induces a decrease in renal plasma flow and glomerular filtration rate. This side effect is usually reversible when CsA dose is reduced. However, even with normal blood levels or during long-term dosage, CsA can produce chronic hypertension and can be the cause of irreversible impairment of renal function. 2 The mechanism by which CsA induces hypertension remains unknown.Hepatotoxicity is a less common side effect, which is characterized by cholestasis and metabolic disturbances. 3,4 In isolated perfused rat liver, CsA administration produced a dose-dependent reduction of bile flow, increased the release of cytosolic and mitochondrial enzymes, and decreased oxygen consumption. 3 High blood levels of CsA in human allograft recipients have been associated with an increase in ␥-glutamyl transpeptidase, a liver enzyme that correlates with hepatotoxicity. 5 In one study, hepatic abnormalities developed in up to 32% of patients with endogenous uveitis treated with CsA. 6 CsA toxicity has been attributed to an imbalance of vasoactive substance release. 1 Recent studies have shown that nitric oxide (NO) is increased during CsA administration by a mechanism th...