ACE inhibition reduces infarction in normotensive but not hypertensive rats: correlation with cortical ACE activity

Abstract

Angiotensin-converting enzyme (ACE) inhibition can reduce stroke risk by up to 43% in humans and reduce the associated disability, and hence understanding the mechanism of improvement is important. In animals and humans, these effects may be independent of the blood pressure-lowering effects of ACE inhibition. Normotensive (Wistar-Kyoto (WKY)) and hypertensive (spontaneously hypertensive rat (SHR)) animals were treated with the ACE inhibitors ramipril or lisinopril for 7 or 42 days before 2 hours of transient middle cerebral artery occlusion (MCAo). Blood pressure, serum ACE, and blood glucose levels were measured and stroke infarct volume was recorded 24 hours after stroke. Despite greater reductions in blood pressure, infarct size was not improved by ACE inhibition in hypertensive animals. Short-term ACE inhibition produced only a modest reduction in blood pressure, but WKY rats showed marked reductions in infarct volume. Long-term ACE inhibition had additional reductions in blood pressure; however, infarct volumes in WKY rats did not improve further but worsened. WKY rats differed from SHR in having marked cortical ACE activity that was highly sensitive to ACE inhibition. The beneficial effects of ACE inhibition on infarct volume in normotensive rats do not correlate with changes in blood pressure. However, WKY rats have ACE inhibitor-sensitive cortical ACE activity that is lacking in the SHR.

Figure 1

Serum angiotensin-converting enzyme (ACE) activity (U/L) in aged animals after vehicle or short-term (ST; 7 days) or long-term (LT; 28 days) treatment with ACE inhibitors ramipril or lisinopril in spontaneously hypertensive rats (SHR; □) and Wistar–Kyoto (WKY; ▪) rats (mean±s.d.), ^***P⩽0.0001 and ^*P⩽0.05 compared with strain vehicle analysis of variance (ANOVA) Dunnett's post hoc test. ^#P⩽2 × 10⁻⁶ (Student's t-test), comparison with strain control treatment.

Figure 2

Photomicrographs of ¹²⁵I-MK351A binding: (A) Wistar–Kyoto (WKY) vehicle; (B) spontaneously hypertensive rat (SHR) vehicle; (C) WKY ramipril (7 days); and (D) SHR ramipril (7 days). Quantitation of binding (c.p.m./mm²) for cortical and subcortical areas in WKY and SHR strains (mean±s.d.). ^***P⩽0.0001 compared with strain vehicle analysis of variance (ANOVA) using Dunnett's post hoc test.

Figure 3

(A) Total infarct volume, (B) cortical infarct volume, and (C) subcortical infarct volume (mm³) in aged animals after vehicle, short-term (7 days), or long-term (28 days) treatment with angiotensin-converting enzyme (ACE) inhibitors ramipril or lisinopril in spontaneously hypertensive rats (SHR; □) and Wistar–Kyoto (WKY; ▪) rats (mean± s.d.). ^*P⩽0.05 compared with to strain vehicle analysis of variance (ANOVA) using Dunnett's post hoc test.