Effects of chronic volume expansion and enalapril on chronic cyclosporine nephropathy
Prolonged treatment with cyclosporine (CS) results in an irreversible renal lesion consisting of interstitial fibrosis and tubular atrophy, as well as prominent hyperplasia of the juxtaglomerular apparatus (JGA). Ischemia to the tubulointerstitial compartment caused by intense CS-mediated renal vasoconstriction may contribute significantly to the development of this lesion. To explore the potential role of volume contraction and activation of the renin-angiotensin system (RAS) in the genesis of this lesion, we have employed a recently described rodent model of chronic cyclosporine nephropathy (CCN). Over 28 days of CS therapy, animals received plain drinking water, 1% saline, or enalapril (ENAL), 50 mg/l in drinking water. At the end of 28 days, Na+ balance in saline-treated animals was markedly positive, and plasma volume was increased; however, glomerular filtration rate (GFR) did not change, and the tubulointerstitial lesion and JGA hyperplasia as evaluated by morphometric techniques were unaffected. Enalapril-treated animals were relatively hypotensive with lower GFR than CS controls. Enalapril conferred no protection against the development of tubulointerstitial disease and exacerbated the development of JGA hyperplasia and hyperkalemia. We conclude that volume contraction is not an important contributor to the reduced GFR, tubulointerstitial lesion, or JGA hyperplasia associated with long-term CS treatment. Blockade of the RAS also conferred no protection against the development of tubulointerstitial disease but resulted in worsening of JGA hyperplasia and hyperkalemia.