Stimulatory effect of dietary lipid and cholestyramine on hepatic HMG CoA reductase.

The diurnal cycle of hepatic HMG CoA reductase activity was studied under conditions of controlled feeding where the percentage of dietary lipid, alone or in combination with 2% cholestyramine, was varied. Cholestyramine caused an increase in HMG CoA reductase activity that began soon after feeding started and peaked 6 hr later. In contrast, a diet containing 20% corn oil was a much weaker inducer of the enzyme but caused a prolonged elevation that began late in the fasting part of the cycle. These patterns suggest two different mechanisms of action.