In Vitro Responses of Human Peripheral Small Arteries in Hypercholesterolemia and Effects of Therapy

Abstract

Studies in both animals and humans with raised lipid levels have demonstrated abnormalities in vascular function usually manifested by an impairment in endothelium-dependent vasorelaxation. This is believed to be an early event in atheroma formation. There are few data on the effects on vascular function in humans of lowering serum lipids. We conducted a study to investigate the effects of cholesterol reduction on the in vitro function of human peripheral small arteries in middle-aged patients with hypercholesterolemia. Subcutaneous gluteal fat biopsies were taken from 18 hypercholesterolemic (HC) patients (mean +/- SEM serum total cholesterol, 9.7 +/- 0.57 mmol/L) and 16 age- and sex-matched control subjects (mean cholesterol, 4.69 +/- 0.18 mmol/L). Subcutaneous small arteries (internal diameter, < 330 microns) were dissected and mounted on a wire myograph for isometric tension measurements. The HC patients showed impaired relaxation to acetylcholine (10(-9) to 10(-6) mol/L) after preconstriction with the thromboxane A2 analogue U46619 (10(-6) mol/L, mean maximum relaxation, 42.9 +/- 5.4%) compared with control subjects (85.7 +/- 4.0%, P < .00001). Incubation with the nitric oxide substrate L-arginine (3 mmol/L) improved the endothelium-dependent vasorelaxation response to acetylcholine (70.9 +/- 6.0%, P < .01) in patients but not in control subjects. Also, there was a smaller but significant difference in responses to the endothelium-independent agent sodium nitroprusside (10(-9) to 10(-6) mol/L) between the HC group (mean maximum relaxation, 76.9 +/- 6.0%) and the control subjects (89.7 +/- 6%; P < .01). A total of 10 patients had a second gluteal skin biopsy and repeat functional studies after successful cholesterol-lowering therapy after a mean period of 9.9 +/- 4.7 months. A significant reduction in total and LDL cholesterol was achieved (5.29 +/- 0.2 and 3.23 +/- 0.21 mmol/L, respectively; P < .001). This restored vasorelaxation to control values in response to both acetylcholine (mean maximum relaxation, 83.3 +/- 3.8%; P < .0001) and sodium nitroprusside (87.9 +/- 4.8%, P < .01). Although both groups were normotensive, there were significantly higher blood pressures in the HC group compared with control subjects (139 +/- 4.1 versus 123 +/- 3.0 mm Hg systolic, P < .01; 84 +/- 1.3 versus 75 +/- 2.2 mm Hg diastolic, P < .01). There was no difference in initial blood pressures between the entire group of 18 and the 10 patients who had repeat biopsies. The blood pressures fell to control values after cholesterol reduction (129.33 +/- 4.93 mm Hg systolic and 72.33 +/- 2.93 diastolic mm Hg, P < .02 relative to pretreatment values). These results demonstrate abnormalities of both endothelium-dependent and -independent relaxation in human peripheral small arteries that are normalized with effective lipid lowering. The changes in blood pressure may have been secondary to the improvement in vascular function.