Vasodilation in Cholesterol-Fed Rabbits

Evidence exists that an endothelium-derived relaxing factor is nitric oxide and that L-arginine is the precursor for the synthesis of nitric oxide in vitro. Whether exogenous L-arginine contributes to the modulation of vascular smooth muscle tone in vivo is still controversial. In hypercholesterolemia, resistance vessels do not relax normally in response to pharmacological stimuli that release endothelium-derived relaxing factor; bioassay experiments have suggested that impaired synthesis or release of endothelium-derived relaxing factor accounts, in part, for this blunted relaxation. We hypothesized that hypercholesterolemia reduces arginine metabolism and thereby impairs endothelium-derived relaxing factor synthesis. Accordingly, we designed a study to determine whether exogenous L-arginine could augment endotheliumdependent vasodilation of hind limb resistance vessels in anesthetized cholesterol-fed rabbits. Femoral blood flow was recorded with an electromagnetic flow probe in 16 cholesterol-fed and 12 control rabbits. The hind limb vasodilator responses to incremental intra-arterial infusions of acetylcholine (0.3-9.0 ,ig/kg/min) and nitroprusside (0.3-9.0 ,ug/kg/min) were studied before and during intravenous administration of L-arginine (10 mg/kg/min), D-arginine (10 mg/kg/min), or saline. The vasodilator response to acetylcholine was impaired in cholesterolfed rabbits as compared with control rabbits. L-Arginine augmented vasodilation to acetylcholine in cholesterol-fed but not in control rabbits. L-Arginine did not alter the effect of nitroprusside in either group. Neither saline nor D-arginine changed the response to either acetylcholine or nitroprusside. Our data demonstrate that exogenous L-arginine normalizes the endothelium-dependent vasodilation of hind limb resistance vessels in cholesterol-fed rabbits. (Circulation Research 1990;67:1301-1308)