Production of Arterial Lesions by a Humoral Factor in Parabiotic Rats

The experimental production of arteriosclerosis and atherosclerosis by RES blocking agents such as colloidal carbon and thorium dioxide has implicated the RES as a factor in the etiology of these diseases. Holtzman strain male rats each received a single intravenous injection of colloidal carbon (5 mg/100 g animal body wt). Three days later the injected animals were united by parabiosis to non-injected animals of the same sex, weight and genetic strain. Carbon granules were found in the RES of injected rats, but few or no granules were found in Kupffer cells of their non-injected parabiotic partners. Coronary arteries of both injected and non-injected animals showed thickening and fragmentation of the internal elastic membrane after two months. After four to six months the lesions included degenerative changes of muscle cells just external to the internal elastic membrane and thickening of the intima. Hyperplasia of the thyroid was found in both parabionts. Addition of 1% cholesterol-5% fat to the diet caused deposition of lipid in endothelial cells and intimal macrophages of the damaged arteries of both parabionts. Distribution of lipid within the hepatic parenchymal cells was also altered in the experimental animals but not in controls. It is suggested that uptake of particulate matter by cells of the RES causes them to release a substance capable of producing arterial lesions.