Failure of hypercholesterolemic serum to stimulate collagen synthesis in aortic smooth muscle cells from two species of nonhuman primates having different rates of collagen synthesis.

African green monkeys develop atherosclerotic lesions that are more fibrous than those found in rhesus monkeys. The purpose of this study was to determine if this difference in collagen content could be related to a specific effect of a serum component on collagen synthesis by cells of the arterial wall or to inherent differences in the arterial smooth muscle cells from these two nonhuman primate species. Aortic smooth muscle cells were grown in tissue culture from both rhesus and African green monkeys and incubated for up to 48 hr with different concentrations of serum from normal or hypercholesterolemic animals. Collagen synthesis was determined by measuring the conversion of radiolabeled proline to hydroxyproline. Total protein synthesis was determined from the incorporation of radiolabeled proline into total proteins. Hypercholesterolemic serum from either species did not stimulate collagen or total protein synthesis in either African green or rhesus monkey smooth muscle cells. This was true even though under the same conditions other studies have shown that hypercholesterolemic serum produces an increase in cellular cholesteryl ester content. This suggests that hypercholesterolemia per se is not directly responsible for the stimulation of collagen synthesis typically seen in atherosclerotic lesions. African green monkey smooth muscle cells synthesized from 1.7 to 3.4 times more collagen than did rhesus monkey smooth muscle cells, while total protein synthesis was similar for both cell types. This suggests that the greater amounts of collagen present in the atherosclerotic lesions from African green monkeys may be in part the result of an inherently greater potential of their smooth muscle cells to synthesize collagen.