DECREASE OF CHOLESTEROL TURNOVER IN OLD RATS

Serum cholesterol is significantly higher in 13-month old male Sprague-Dawley rats than in 2-months old animals. 1 day after i.v. injections of cholesterol-7-3H, (the same dose according to body wt.) serum level of the isotope is much higher in the older group and the decrease of serum radioactivity from 24 to 72 hr is faster in the younger animals. Incorporation of 3H-cholesterol into the aorta is much lower in older animals if the incorporation into the aorta is corrected according to the blood isotope level. After the ligation of the common bile duct for 3 days the differences in serum isotope level in young and old animals is smaller but remains significant. It is concluded that both slower incorporation into the tissues and slower cholesterol excretion are responsible for higher 3H-cholesterol level in the blood of older animals. Slower incorporation of cholesterol in the aorta of old animals in vivo corresponds to the previously described experiments in vitro. © 1969.