The cholesterol in the plasma lipoprotein, most of it comes from the synthesis of the body rather than from food. The way to synthesize cholesterol in vivo is shown in Fig. 33-2. The-reductase converts-to methyl valerate (MEVILONICACID), an early-stage speed-limiting step in the synthesis of cholesterol, which is regulated by cholesterol metabolism in the body. The emptying of the intracellular cholesterol pool causes the enzyme activity to increase, thus accelerating the synthesis of cholesterol in vivo. When the amount of cholesterol in the cell increases, the activity of the enzyme decreases and the synthesis of cholesterol in vivo slows down.

The open acid portion of the chemical structure of-reductase inhibitor is very similar to that of-, and has a specific competitive inhibition on the cholesterol biosynthesis of the enzyme--hmg-coa reductase. In theory it can inhibit the formation of all the metabolites of the methyl valerate-cholesterol, terpene alcohol and coenzyme Q (Fig. 33-2). The study confirms that although it can reduce cholesterol production, it has little effect on overall metabolism.