Dietary arginine prevents atherogenesis in the coronary artery of the hypercholesterolemic rabbit.

OBJECTIVES

This study was designed to test the hypothesis that long-term oral supplementation of dietary L-arginine (to provide a sustained elevation of nitric oxide activity) would inhibit atherogenesis in hypercholesterolemic rabbits, as assessed by histomorphometric measurements.

BACKGROUND

Endothelium-derived nitric oxide inhibits a number of processes that are critical in atherogenesis. Hypercholesterolemia reduces endothelial nitric oxide activity, and we postulate that this may promote atherogenesis. This reduction in nitric oxide activity can be reversed acutely by intravenous infusion of L-arginine, the precursor of nitric oxide. We show that dietary supplementation of L-arginine abrogates the development of coronary atheroma in hypercholesterolemic rabbits.

METHODS

Male New Zealand White rabbits were fed normal rabbit chow, 1% cholesterol chow or 1% cholesterol chow with dietary arginine or methionine supplementation to increase their intake of these amino acids sixfold. After 1 or 10 weeks of dietary intervention, the left main and left anterior descending coronary arteries were harvested for histologic study. Plasma cholesterol measurements were elevated to the same degree in all groups of rabbits receiving the 1% cholesterol diet, whereas plasma arginine levels were doubled in the arginine-treated group. High density lipoprotein (HDL) cholesterol values were not affected by arginine treatment.

RESULTS

In rabbits receiving the 1% cholesterol diet, with or without methionine supplementation, light and electron microscopy revealed a marked increase from 1 to 10 weeks in the intimal accumulation of macrophages, associated with an increase in the intimal area of the left main coronary artery. By contrast, in arginine-treated hypercholesterolemic rabbits, there was a near absence of adherent monocytes and tissue macrophages and no progression of intimal thickness from 1 to 10 weeks.

CONCLUSIONS

Dietary supplements of L-arginine prevent intimal thickening in the coronary arteries of hypercholesterolemic rabbits. This antiatherogenic effect is not due to an alteration in plasma total cholesterol, HDL cholesterol or caloric or nitrogen balance. The data are consistent with the hypothesis that nitric oxide has antiatherogenic properties.