Atorvastatin Action Involves Diminished Recovery of Hepatic HMG-CoA Reductase Activity

The effects of atorvastatin on the expression of the hepatic HMG-CoA reductase and LDL receptor genes were investigated in rats. Like the other statins, atorvastatin increased the rate of degradation and presumably cycling of the hepatic LDL receptor. In atorvastatin-treated rats, the half-life of the receptor was decreased by over 60%. Hepatic HMG-CoA reductase mRNA levels were increased about 3-fold by feeding a diet containing 0.04% atorvastatin while reductase protein levels were increased by as much as 700-fold. Apparent HMG-CoA reductase activity was not increased as much as protein levels. Washing experiments revealed that atorvastatin is more difficult to remove from microsomes than lovastatin. The results support the conclusion that the potent hypocholesterolemic action of atorvastatin involves decreased hepatic VLDL production due to effective inhibition of in vivo cholesterol biosynthesis resulting from diminished recovery of HMG-CoA reductase activity following drug treatment.