Effects of Losartan and Enalapril on Small Artery Structure in Hypertensive Rats

We evaluated the effects on cardiovascular structure of the angiotensin-converting enzyme (ACE) inhibitor enalapril and of the angiotensin II receptor blocker losartan, administered either at hypotensive or nonhypotensive dosage in spontaneously hypertensive rats (SHR). SHR were treated from ages 4 to 12 weeks with low-dose (1 mg [middle dot] kg [middle dot] d) enalapril, low-dose (0.5 mg [middle dot] kg () [middle dot] d) losartan, high-dose (25 mg [middle dot] kg [middle dot] d) enalapril, or high-dose (15 mg [middle dot] kg [middle dot] d) losartan. Untreated WKY and SHR were also studied. Rats were killed at 13 weeks of age, and the heart was weighed. Mesenteric small arteries were dissected and mounted on a micromyograph for determination of media thickness and lumen diameter. In fixed arteries, cell volume, number of cells per segment length, and number of cell layers were measured using the unbiased "disector" method. Systolic blood pressure was significantly reduced by the high doses of both drugs, but the hypotensive effect was greater with enalapril than with losartan (P