Decrease of excretion of cholesterol during aging

Abstract

Excretion of tritium was measured in feces after i.v. injection of 3H-cholesterol to young (2·5 months) and old (14 months) rats. Excretion of catabolic products of 3H-cholesterol was by about 70 per cent smaller in older animals which may partly explain their higher retention of 3H-cholesterol in the blood. Excretion of 3H-cholesterol in the steroid fraction of feces was decreased more than excretion of tritium in the rest of feces which is mainly bile acid fraction. After ligature of the common bile duct which excludes bile secretion the decrease of excretion of 3H-cholesterol in older animals remains, showing that also intestinal secretion of cholesterol is smaller in older rats. Possible effect of smaller spontaneous food intake of older animals on excretion of cholesterol was excluded by pair-feeding of the younger animals. A hypothesis is advanced that formation of bile acids from cholesterol is decreased in older animals. After parabiotic connection of young and old rats, excretion of 3H-cholesterol was increased in the old parabiotic partners and also turnover of 3H-cholesterol tissues was increased to the level observed in young animals. This points to a presence of humoral factors in the blood of young and old animals effecting metabolism of cholesterol.