Chronic treatment with cyclosporine (CsA) is limited not only by glomerular hypofiltration but also by structural damage. The pathogenesis of these nephrotoxicities was studied in a model of chronic CsA-induced renal damage. Salt-depleted rats were treated with daily CsA (15 mg/kg sc) for approximately 3 weeks, at which time renal function was measured and kidneys were harvested for morphologic assessment. A separate group of rats (CsA + BQ123) were identically treated with CsA but in addition also received simultaneous treatment with a specific endothelin A (EtA) receptor antagonist, BQ123, which was continuously delivered via sc osmotic pump (1 mg/kg per hour) and maintained throughout the study. Chronic CsA treatment caused profound functional and structural damage, although blood pressure was normal (102 +/- 6 mm Hg); GFR was 0.05 +/- 0.02 mL/min per 100 g body wt, and RPF was 0.15 +/- 0.06/100 g body wt. Renal injury was scored on a scale of 0 to 4 and showed dilation/vacuolization of 1.07 +/- 0.29 and tubulointerstitial fibrosis of 0.78 +/- 0.17. Arteriolopathy was present in 78 +/- 4% of arterioles. Chronic antagonism of the EtA receptor preserved renal function: GFR was 0.15 +/- 0.03 mL/min per 100 g body wt, and RPF was 0.32 +/- 0.08/100 g body wt (P < 0.05 for GFR versus CsA). Blood pressure was not affected: 104 +/- 8 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)