Calcium antagonists and converting enzyme inhibitors reduce renal injury by different mechanisms

Both glomerular hypertension and hypertrophy have been associated with the development of glomerular injury in models of hypertension and reduced renal mass. The purpose of this study was to examine the effects of antihypertensive therapy on these parameters in the remnant kidney model of progressive glomerular sclerosis. Rats underwent 5/6 nephrectomy and were randomly assigned to receive either no therapy, the calcium entry blocker (CEB), nifedipine, or the angiotensin converting enzyme inhibitor (CEI), enalapril. Administration of either drug was associated with a reduction in systemic blood pressure and in the severity of glomerular injury assessed eight weeks after renal ablation. Micropuncture studies four weeks after ablation revealed that systemic and glomerular capillary pressure were high in untreated remnant kidney rats and reduced by enalapril. Administration of nifedipine was associated with a decline in systemic pressure, however, plasma renin levels increased, causing efferent arteriolar vasoconstriction and persistence of glomerular hypertension. Morphometric analysis showed that kidney weight, glomerular volume and glomerular capillary radius were lower in nifedipine treated rats than in the other two groups, indicating that the CEB, but not enalapril, inhibited the hypertrophic response to ablation of renal mass. Therefore, both CEIs and CEBs reduce glomerular injury in rats with remnant kidneys but they may act by different mechanisms. CEI reduce glomerular capillary pressure while CEBs inhibit compensatory kidney growth.