Abstract
The effects of dietary fat, cholesterol and insulin administration on the activity of 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoA reductase) in rat liver microsomes, the microsomal cholesterol content and cholesteryl ester content were examined. When corn oil or coconut oil was fed, animals receiving corn oil revealed a higher enzyme activity compared to those receiving coconut oil. Microsomal analysis demonstrated an inverse relationship between the cholesteryl ester contents and activities of HMG-CoA reductase when the enzyme activity was manipulated by the dietary fat or cholesterol, whereas no such relation was observed when the activity was increased by the administration of insulin. The microsomal cholesteryl ester content also remained relatively constant at different stages of the diurnal rhythm of the enzyme. Compared to normal rats, a lower enzyme activity was observed in diabetic rats but no apparent changes in microsomal cholesteryl ester content were seen. The results of the experiments indicated that two kinds of controlling factors of HMG CoA reductase may exist; in one group there is a consistent correlation between the microsomal cholesteryl ester content and the enzyme activity, whereas no such relation is observed in the other.
