Effects of antihypertensive treatment on composition of cerebral arterioles.

Treatment of chronic hypertension with cilazapril, but not hydralazine, attenuates changes in distensibility of cerebral arterioles that occur in stroke-prone spontaneously hypertensive rats (SHRSPs). In this study, effects of antihypertensive treatment on composition of cerebral arterioles was determined in SHRSPs. Cilazapril (45 mg/kg/day), an angiotensin converting enzyme (ACE) inhibitor, or hydralazine (18 mg/kg/day) was begun when rats were 3 months of age. Both cilazapril and hydralazine reduced systolic arterial pressure in SHRSPs (from 199 +/- 6 to 122 +/- 7 mm Hg for cilazapril versus 143 +/- 5 mm Hg for hydralazine [mean +/- SEM]; p less than 0.05). Cerebral arterioles were fixed in vivo, and the cross-sectional area of the vessel wall was measured histologically. In SHRSPs, both cilazapril and hydralazine reduced cross-sectional area of the vessel wall to values obtained in Wistar-Kyoto (WKY) rats. Thus, both cilazapril and hydralazine prevented hypertrophy of cerebral arterioles in SHRSPs. Composition of the arteriolar wall was determined with point counting stereology. Cerebral arterioles in SHRSPs contained significantly more smooth muscle and elastin than in WKY rats (1,294 +/- 157 versus 853 +/- 88 microns2, respectively, for smooth muscle and 148 +/- 13 versus 108 +/- 7 microns2, respectively, for elastin (120 +/- 8 microns2) in cerebral arterioles in SHRSPs was similar to that in WKY rats. Treatment with hydralazine was effective in preventing increases in elastin (128 +/- 14 microns2) and in attenuating increases in smooth muscle (1,008 +/- 18 microns2). The ratio of nondistensible (collagen, basement membrane) to distensible (smooth muscle, elastin, endothelium) components was greater in SHRSPs than in WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)