Previous studies in experimental models of progressive renal failure have shown that the capacity of antihypertensive drugs to protect glomeruli from sclerosis is often unpredictable from their effect on systemic blood pressure. The present study was undertaken to ascertain whether this systemic blood pressure-independent structure-preserving effect of antihypertensives, particularly angiotensin II converting enzyme inhibitors (ACEI), is confined to the glomerulus or not, as well as whether this effect is mediated via angiotensin II (Ang II). The following experimental drug regimens were used in the rat model of subtotal nephrectomy (sNPX): so-called triple therapy [TRX: a combination of reserpine 5 mg/liter drinking water (DW), hydralazine 80 mg/liter DW and hydrochlorothiazide 25 mg/liter DW], or ACEI (either captopril, CPL, 600 mg/liter DW, enalapril, ENL, 400 mg/liter DW or lisinopril, LSL, 200 mg/liter DW). or a novel Ang II receptor antagonist (Ang IIR, L-158.809, 20 mg/liter DW). These dosages were identified in pilot studies to be the minimum required to control systemic blood pressure in the early phase up to 12 weeks. In addition, a separate group was treated with a higher dose of L-158,809 (80 mg/liter DW) with equipotent systemic pressor effect. Treatment was initiated eight weeks after subtotal nephrectomy following renal biopsy, and animals were sacrificed at 16 weeks. In ACEI treated rats, carotid arterial wall thickening (WT), defined as ratio of media thickening to radius of outer vessel wall, was similar to normal age-matched control (0.073 in all ACEI treated rats, vs. 0.074 in normal control) and significantly less than with TRX (ratio 0.118) or untreated sNPX (0.130). Even more remarkably, coronary arteriole WT in ACEI-treated rats averaged 0.139, a value less than one half and one third of TRX (0.298) and untreated sNPX control (0.388), respectively. Similar results were obtained for mesenteric artery WT. These findings were closely paralleled by changes of glomerular sclerosis. In untreated sNPX control rats, glomerular sclerosis increased from biopsy to autopsy specimens by an average of 458%. Although TRX dampened the degree of increase in sclerosis to on average 212%, this protective effect was far less than that achieved by ACEI. In the latter, sclerosis increased on average only 65% from biopsy to autopsy. Although all ACEIs were more effective than TRX, captopril and lisinopril groups showed greatest benefit at these doses. Ang IIR also protected renal and extrarenal structures with 34% increase of sclerosis index in low dose and WT 0.088, 0.117 and 0.112, respectively in carotid, mesenteric and coronary arteries. Higher dose had greater protective effects, although systemic pressures were comparable to the low dose. The findings indicate that in minimum dosages required for controlling systemic blood pressures ACEI and Ang IIR are more potent than other vasodilators in protecting glomerular structure. This greater structure-preserving potency of ACEI and Ang IIR is not limited to the glomerulus, but extends to other systemic vascular beds, where variable lesions also develop in chronic renal failure. The similar results with Ang IIR and ACEI further indicate that the progressive morphological damage of glomerular and extraglomerular vasculatures in chronic renal failure involves local action of angiotensin II.
