Experimental data using diabetic rat models suggested that ACEIs and ARBs have similar beneficial effects. Early studies using the ARB losartan potassium demonstrated reduced BP, proteinuria, and glomerular injury in rats with reduced renal mass.61 In rats with drug-induced diabetes, the ACEI ramipril and the ARB valsartan lowered BP equivalently and prevented the increase in urinary albumin excretion observed in untreated animals.62 Both agents attenuated glomerular structural changes similarly. In another experiment, the ACEI enalapril maleate and the ARB candesartan reduced BP comparably and inhibited proteinuria, glomerulosclerosis, interstitial fibrosis, and inflammation early in the course of treatment in partially nephrectomized rats. However, only candesartan prevented the late progression of glomerulosclerosis and interstitial fibrosis.63 Additional studies in a rat model of hypertensive nephrosclerosis have shown that 22 weeks of treatment with the ACEI delapril hydrochloride or the ARB candesartan produced equivalent renoprotection (reduction in proteinuria and glomerulosclerosis) compared with untreated control rats.64 Similarly, in a study of uninephrectomized hypertensive rats, the ACEI enalapril and the ARB irbesartan decreased BP to within the reference range, lowered proteinuria, markedly reduced glomerulosclerosis, and decreased glomerular capillary pressure while maintaining GFR. Conversely, hypertension, proteinuria, and elevated glomerular capillary pressure developed in untreated rats.65 A study in spontaneously hypertensive rats showed that the ACEI captopril and the ARBs telmisartan and losartan reduced BP similarly and attenuated renal damage by significantly decreasing urinary albumin level and glomerulosclerosis.66 In another study, treatment of male diabetic Munich-Wistar Froemter rats with the ARB valsartan or the ACEI benazepril hydrochloride resulted in normalized systemic and glomerular capillary BP, prevention of proteinuria, and minimized glomerulosclerosis.67 Eprosartan mesylate, a newer ARB, has also been shown to be renoprotective in 5 of 6 nephrectomy models of progressive renal disease in rats.68 Taken together, these studies provide strong evidence that the BP-lowering and renoprotective effects of ARBs are comparable to those of ACEIs in a variety of animal models of chronic, progressive renal disease.