Faculty Bibliography

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

Male Munich-Wistar rats underwent right nephrectomy and infarction of two thirds of the left kidney. Rats were randomly assigned to ingest standard chow (REM) or a moderately salt restricted chow (LS). A third group of rats were fed the low salt diet and were injected with an androgen (LSA). Eight weeks after ablation, glomerular volume and glomerular capillary radius were markedly increased in REM. This increase was prevented by the low salt diet, however, the antihypertrophic effect of the diet was overcome by androgen. Values for glomerular volume and capillary radius were similar in LSA and REM. Morphologic studies revealed that approximately 25% of glomeruli were abnormal in REM. Much less injury was observed in salt restricted rats, however, the protective effect of the low salt diet was significantly abrogated when renal growth was stimulated in salt restricted rats by androgen. Micropuncture studies revealed that glomerular pressure was elevated in all three groups and not affected by diet or androgen. Serum cholesterol was also similar in the three groups. These findings indicate that renal and glomerular hypertrophy are correlated with the development of glomerular injury after reduction in renal mass and suggest that dietary salt restriction lessens renal damage, at least in part, by inhibiting compensatory renal growth

Recent evidence suggests that calcium channel blockers have specific effects on renal hemodynamics in patients with hypertension and may also slow the progression of chronic renal failure. When these agents are studied in vitro, their predominant effect is to reverse afferent arteriolar vasoconstriction induced by catecholamines or angiotensin II. Because efferent resistance may remain high, glomerular filtration rate rises while renal blood flow remains low. The effects in vivo are less consistent. In human hypertension, calcium channel blockers lower renal resistance and may raise both renal blood flow and glomerular filtration rate. In experimental models of chronic renal disease, calcium channel blockers slow the progression of renal damage; however, variable effects on renal hemodynamics have been found. Other factors implicated in the progression of renal damage, including compensatory renal hypertrophy, platelet aggregation, and calcium deposition, may also be favorably influenced by these agents. Recent studies suggest that calcium channel blockers may have similar protective effects in patients with hypertension and chronic renal disease

Male Munich-Wistar rats underwent right nephrectomy and were given weekly injections of deoxycorticosterone acetate (DOCA) and 1% saline (salt) to drink. Two studies were performed. In the first, rats given enalapril (ENP) were compared with controls. In the second, rats ingested either standard chow or chow to which the calcium-entry blocker nifedipine (NIF) had been added. Six to eight weeks after nephrectomy, both control DOCA-salt rats and those given ENP had severe hypertension and significant proteinuria. Rats given NIF excreted less protein, and glomerular lesions were not observed in this group. The effects of NIF on several parameters that have been associated with glomerular injury were examined. Micropuncture studies revealed that glomerular capillary pressure was increased in DOCA-salt rats and was not reduced by NIF. Platelet aggregation was also similar in NIF-treated and control rats. Morphometric studies revealed a tendency toward lower glomerular volume of NIF-treated rats; however, kidney weight and glomerular capillary radius were unaffected by therapy. Thus NIF, but not ENP, prevents DOCA-salt rats from developing hypertension and glomerular injury. This effect does not depend on reduction in glomerular pressure or inhibition of platelet aggregation

Spontaneously hypertensive rats (SHR) were uninephrectomized (UNX) at 6 wk of age and given either standard chow (CON), low-sodium chow (LSC), or standard chow and hydrochlorothiazide (HCTZ) added to the drinking water. Severe hypertension developed in all three groups. Forty-two weeks after UNX, proteinuria and glomerular sclerosis were significantly lower in LSC than in CON or HCTZ. The protective effect of salt restriction did not depend upon alterations in plasma renin concentration or glomerular hemodynamics. Micropuncture revealed that glomerular pressure was high in all three groups. Renal hypertrophy assessed by kidney weight, kidney-to-body weight ratio, glomerular volume, and glomerular capillary radius were reduced by salt restriction. These findings suggest that, in the setting of glomerular hypertension, hypertrophy promotes sclerosis. Salt restriction inhibits compensatory kidney growth and protects the kidney