Studies on Initiating Factors of Atherogenesis

The present studies were undertaken in order to elucidate the effects of oxygen inhalation on plasma lipids and atherogenesis.Eleven male Japanese white rabbits were fed on standard rabbit pellet plus 1% cholesterol. Six among 11 rabbits were exposed to 40% oxygen (hyperoxic) and 5 were exposed to 21% oxygen (control), respectively, for 5 hrs on 5 days of each week for 8 weeks. Obtained results were as follows:1) Degree of the sudanophilic aortic lesion in hyperoxic rabbits was less than control, especially in the aortic arch and the abdominal aorta.2) There were no differences of hydroxyproline contents of the aortic intima and media between both groups.3) Levels of plasma lipids (cholesterool, triglyceride, phospholipid and lipoperoxide) were greatly increased in both groups.4) A slight increase in HDL cholesterol was seen, but there were no differnces between both groups.From these results, it is postulated that the progress in atheromatous change of the aorta may be supressed by oxygen inhalation not through the change in pattern of the plasma lipids, but through the direct effect on the aortic wall. We proposed a hypothesis that tissue hypoxia induced by hyperlipidemia might play an important role in the early deposition of lipids in the aortic wall.