Effects of an angiotensin-converting enzyme inhibitor and a beta-blocker on cerebral arterioles in rats

We examined the effects of an angiotensin-converting enzyme inhibitor, perindopril, and a beta-blocker, propranolol, on cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP). The structure and mechanics of cerebral arterioles were examined in untreated Wistar-Kyoto rats (WKY) and SHRSP that were untreated or treated for 3 months with a high (2 mg/kg per day) or a low (0.3 mg/kg per day) dose of perindopril or propranolol (250 mg/kg per day) alone or in combination with the low dose of perindopril. We measured pressure, external diameter, and cross-sectional area of the vessel wall (CSA) in maximally dilated (with EDTA) cerebral arterioles. Treatment of SHRSP with the high dose of perindopril or the combination of propranolol and the low dose of perindopril normalized cerebral arteriolar mean pressure (50+/-1 mean+/-SEM] and 43+/-2 mm Hg vs 50+/-1 mm Hg in WKY and 94+/-3 mm Hg in untreated SHRSP; P<0.05), pulse pressure (15+/-1 and 16+/-1 mm Hg vs 13+/-1 mm Hg in WKY and 35+/-1 mm Hg in untreated SHRSP; P<0.05), and CSA (1103+/-53 and 1099+/-51 microm2, respectively, vs 1057+/-49 microm2 in WKY and 1281+/-62 microm2 in untreated SHRSP; P<0.05). In contrast, treatment of SHRSP with the low dose of perindopril or propranolol alone did not normalize arteriolar pulse pressure (24+/-1 and 21+/-1 mm Hg) and failed to prevent increases in CSA (1282+/-77 and 1267+/-94 microm2). Treatment with either dose of perindopril or the combination of propranolol and perindopril significantly increased external diameter in cerebral arterioles of SHRSP (99+/-3, 103+/-2, and 98+/-3 microm vs 87+/-2 microm in untreated SHRSP; P<0.05), whereas propranolol alone did not (94+/-3 microm; P>0.05). These findings suggest that effects of angiotensin-converting enzyme inhibitors on cerebral arteriolar hypertrophy in SHRSP may depend primarily on their effects on arterial pressure, particularly pulse pressure, whereas their effects on cerebral arteriolar remodeling (defined as a reduction in external diameter) may be pressure independent.