Effect of long-term administration of AY-9944, an inhibitor of 7-dehydrocholesterol delta 7-reductase, on serum and tissue lipids in the rat.

The effect of long-term administration of AY-9944, a specific inhibitor of cholesterol biosynthesis, was examined in rats maintained on diets with low and high cholesterol and fat content. Sterol and phospholipid levels were determined in the serum, liver, adrenals, lungs, and brain after 6 and 12 months of feeding AY-9944 at several dose levels. In all the tissues examined, the cholesterol content was lowered and the cholesterol was partly replaced by 7-dehydrocholesterol biosynthesized instead of cholesterol in the presence of AY-9944. Cholesterol levels were particularly low in the serum and adrenals, while 7-dehydrocholesterol accumulated in the lungs. The fall in cholesterol and appearance of 7-dehydrocholesterol were reversible. Alterations of this type in the brain indicated that sterol metabolism is active in the adult rat brain. Addition of cholesterol to the diet reduced the effect of the inhibitor by eliminating the liver as a site of sterol synthesis.