L-arginine restores dilator responses of the basilar artery to acetylcholine during chronic hypertension

The objective of this study was to test the hypothesis that administration of L-arginine, a substrate for nitric oxide synthase, restores acetylcholine- induced dilatation of the basilar artery in chronically hypertensive rats. Basilar artery diameter was measured through a cranial window in anesthetized stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar- Kyoto rats (WKY) aged 6 to 7 months (adult) and 12 months (older adult). Under control conditions, baseline basilar artery diameter was smaller in SHRSP (adult, 239±30 μm; older adult, 198±13 μm) (mean±SE) than in WKY (adult, 261±10 μm; older adult, 259±7 μm) (P<.05 versus SHRSP). Topical application of acetylcholine (10^-5 mol/L) produced dilatation of the basilar artery in WKY, which was impaired in both adult and older SHRSP (P<.05). Topical L-arginine (10^-3 mol/L for 30 minutes) did not affect responses to acetylcholine in adult SHRSP but enhanced vasodilatation in response to acetylcholine (10^-5 mol/L) in older SHRSP without affecting responses to sodium nitroprusside. In contrast, D-arginine did not affect acetylcholine-induced vasodilatation in older SHRSP. These results suggest that impaired dilatation of the basilar artery in response to acetylcholine in older SHRSP is restored toward normal by L-arginine, a substrate for nitric oxide synthase.