Endothelium-dependent relaxation in resistance arteries from spontaneously hypertensive rats: effect of long-term treatment with perindopril, quinapril, hydralazine or amlodipine

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Abstract
To examine the effects of different types of antihypertensive treatment on endothelium-dependent relaxation in resistance arteries from spontaneously hypertensive rats (SHRs). Three-week-old SHRs were treated with the angiotensin converting enzyme (ACE) inhibitor perindopril (1 mg/kg/day) or quinapril (3 mg/kg/day) or the vasodilator hydralazine (50 mg/kg/day) or the calcium antagonist amlodipine (10 mg/kg/day). Control SHRs and Wistar-Kyoto (WKY) rats were treated with water. After 21 weeks rats were culled and mesenteric resistance arteries were mounted in a myograph. Relaxation responses to the endothelium-dependent vasodilators acetylcholine (ACh) and bradykinin were recorded before and after incubation with the nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NOARG), as was the relaxation response to the nitric oxide donor sodium nitroprusside (SNP). All drugs prevented the rise in blood pressure found in the untreated SHRs. ACh-induced relaxation was significantly impaired in the untreated SHRs compared with the WKY rats. Treatment with either ACE inhibitor prevented the development of this impaired response. ACE inhibitor treatment significantly increased the relaxation response to bradykinin. Despite lowering blood pressure, hydralazine or amlodipine had no effect on ACh- or bradykinin-induced relaxation. Responses to SNP were not different between untreated SHRs and WKY rats and were not affected by drug treatment. Specific properties of certain antihypertensive drugs may play an important role in restoring endothelium-dependent relaxation in the small arteries that regulate peripheral resistance in the SHR.