Nitric Oxide Release From Kidneys of Hypertensive Rats Treated With Imidapril

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Abstract
Abstract To examine whether endothelial dysfunction in hypertension is reversible or not, we studied the effects of imidapril, an angiotensin-converting enzyme inhibitor, on nitric oxide release in stroke-prone spontaneously hypertensive rats (SHR) and deoxycorticosterone acetate (DOCA)–salt hypertensive rats. After a 4-week treatment with imidapril (1 or 10 mg/d SC) or vehicle, acetylcholine-induced vasodilation and nitric oxide release in the isolated kidneys were determined. Nitric oxide release was measured by a chemiluminescence assay. Imidapril lowered blood pressure in stroke-prone SHR in a dose-dependent manner. Untreated stroke-prone SHR exhibited significantly attenuated responses to acetylcholine (10 −8 mol/L) of both renal perfusion pressure (stroke-prone SHR 42±4% versus Wistar-Kyoto rats [WKY] 58±4% [mean±SE], P <.01) and nitric oxide release (stroke-prone SHR +7.6±2.1 versus WKY +29.7±9.7 fmol/min per gram of kidney wt, P <.01). Imidapril at 10 mg/d significantly increased acetylcholine-induced renal vasodilation and nitric oxide release in stroke-prone SHR (renal perfusion pressure, 56±3%; nitric oxide release, +27.1±6.4 fmol/min per gram of kidney wt; both P <.01 versus stroke-prone SHR treated with vehicle). On the other hand, imidapril neither decreased blood pressure nor changed nitric oxide release induced by acetylcholine in DOCA–salt hypertensive rats. Staining for endothelial nitric oxide synthase and brain nitric oxide synthase was clearly detected in the kidneys of both stroke-prone SHR and WKY, whereas staining intensity was weaker in DOCA–salt hypertensive rats. Inducible nitric oxide synthase immunoreactivity was barely noticeable in any type of rat. Thus, imidapril restored endothelial damage by pressure-dependent mechanisms. Most of the nitric oxide detected in the perfusate seemed to be derived from constitutive nitric oxide synthase.