Sympathetic activity, lipids accumulation, and arterial wall morphology in rabbits at high altitude

The purpose of this study was to investigate the effect of increased sympathetic nervous activity on arterial wall viability as reflected by its response to elevated plasma lipids. Our previous finding that vascular wall viability was reduced by low sympathetic nervous activity indicated that chronically enhanced sympathetic activity should have the opposite effect. In this study rabbits were divided into two groups, both of which received 1% cholesterol in the diet. One group was born and raised at high altitude to induce chronic activation of sympathetic activity, and the other was raised at sea level. Aorta of high-altitude rabbits exhibited significantly less lipid accumulation than aortas of sea-level rabbits. This difference in lipid accumulation was accompanied by elevated norepinephrine turnover and decreased sensitivity to exogenous norepinephrine of high-altitude rabbit arteries. Vascular smooth muscle cells of high-altitude rabbits demonstrated striated increased relative volume density of mitochondria and decreased nucleocytoplasmic ratio, reflecting lower mitotic rate. These results are suggestive that enhanced chronic activity of vascular sympathetic innervation protects smooth muscle from lipid accumulation and exerts a positive effect on vascular viability.