Production of arterial lesions by a humoral factor in parabiotic rats.

• Arterial lesions resembling arteriosclerosis produced by reticuloendothelial system blockade have been demonstrated by Patek and Bernickwho injected carbon or thorium dioxide into rats and rabbits; by Shimamoto who injected tissue and bacterial potysaecharides, bacterial exotoxins, killed bacteria, dextran and glycogen, and kaolin into rabbits, rats and guinea pigs; by Lautsch et al. who injected thorium dioxide into rabbits and by Hueper who injected polyvinyl alcohol into dogs. The appearance of particles of the suspensions in endothelial cells or macrophages of the arterial intima has been observed following massive or repeated injections of these substances" and has indicated the possibility of a direct effect of these substances on endothelium. Single, relatively small doses of colloidal suspensions, however, can produce vascular lesions which do not contain any of this particulate material.'' Therefore, it can be assumed tliat the resultant vascular pathology was not directly caused by the particulate materials themselves, but was probably related to the effects of particulate material upon the reticuloendothelial system of macrophages. Experiments described below were designed to test the hypothesis that a humoral factor may be involved in production of the arterial lesions which follow blockade of the reticuloendothelial system by particulate matter.