Effects of antihypertensive therapy on mechanics of cerebral arterioles in rats. The purpose of this study was to examine effects of antihypertensive treatment on structure and mechanics of cerebral arterioles and the incidence of stroke in stroke-prone spontaneously hypertensive rats (SHRSP). Treatment of hypertension was begun at 3 months of age with cilazapril (45 mg/kg/day), an angiotensin converting enzyme (ACE) inhibitor, or with hydralazine (18 mg/kg/day). Cilazapril and hydralazine reduced systolic arterial pressure (from 195 +/- 8 to 125 +/- 5 and 148 +/- 3 mm Hg, respectively [mean +/- SEM]; p less than 0.05). To examine structure and mechanics of cerebral arterioles, we measured pressure (servonull), external diameter, and cross-sectional area of the vessel wall (histologically) in pial arterioles of normotensive Wistar-Kyoto (WKY) rats and SHRSP that were untreated or that were treated for 3 months with cilazapril or with hydralazine. Arterioles were maximally dilated with EDTA. In WKY rats, cilazapril and hydralazine did not alter pial arteriolar pressure, external diameter, or cross-sectional area of the vessel wall. In SHRSP, both cilazapril and hydralazine reduced cross-sectional area of the vessel wall to levels not significantly different from WKY rats (from 1,911 +/- 155 to 1,244 +/- 101 and 1,388 +/- 59 microns 2, respectively, compared with 1,405 +/- 95 microns 2 for untreated WKY rats). Cilazapril was more effective than hydralazine in reducing pial arteriolar pressure (from 110 +/- 6 to 62 +/- 2 mm Hg with cilazapril versus 79 +/- 5 mm Hg for hydralazine compared with 60 +/- 4 mm Hg for untreated WKY rats). Cilazapril, but not hydralazine, attenuated reductions in external diameter of pial arterioles (from 91 +/- 4 to 100 +/- 4 microns for cilazapril versus 91 +/- 3 microns for hydralazine compared with 107 +/- 3 microns for untreated WKY rats). 