Abstract
Cholesterol metabolism was studied in relation to aging 8'88 week old in Wistar male rats. The levels of cholesterol in serum, liver and arterial wall, the incorporation of 14C-labelled precursors in the cholesterol of those tissue and the activity of some enzymes related to cholesterol turnover were assayed. The first period, up to about 16 weeks, is a growing stage in which the gain of body weight is most significant. In this stage serum cholesterol increases mostly from exogenous sources, and tissue cells accumulate cholesterol from LDL for their needs. The synthesis of cholesterol in liver seems to be repressed by the well-known feed back mechanism. In the second period, between approximately 16 and 36 weeks, increase in body weight still continues but the level of serum cholesterol remains constant. Cholesterol synthesis is suggested to be higher than in the first period, so its degradation to bile acids is considered to be somewhat greater. The metabolism of cholesterol appears to be well balanced as a whole. However, in the third period from 36 to 47 weeks, serum cholesterol tends to increase, especially LDL cholesterol. The catabolism of cholesterol probably decreases in this stage to break the balance. HDL cholesterol levels in rats behave with aging in a somewhat different way than in humans, and this may explain why rat are resistant to atherosclerosis.
