Ubiquinone is a carrier of the mitochondrial respiratory chain which regulates oxidative phosphorylation: it also acts as a membrane stabilizer preventing lipid peroxidation. In man the quinone ring originates from tyrosine, while the formation of the polyisoprenoid lateral chain starts from acetyl CoA and proceeds through mevalonate and isopentenylpyrophosphate; this biosynthetic pathway is the same as the cholesterol one. We therefore performed this study to evaluate whether statins (hypocholesterolemic drugs that inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase) modify blood levels of ubiquinone. Thirty unrelated outpatients with primary hypercholesterolemia (IIa phenotype) were treated with 20 mg of simvastatin for a 3-month period (group S) or with 20 mg of simvastatin plus 100 mg CoQ10 (group US). The following parameters were evaluated at time 0, and at 45 and 90 days: total plasma cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, triglycerides, Apo A1, Apo B and CoQ10 in plasma and in platelets. In the S group, there was a marked decrease in total cholesterol low-density lipoprotein-cholesterol and in plasma CoQ10 levels from 1.08 mg/dl to 0.80 mg/dl. In contrast, in the US group we observed a significant increase of plasma CoQ10 (from 1.20 to 1.48 mg/dl) while the hypocholesterolemic effect was similar to that observed in the S group. Platelet CoQ10 also decreased in the S group (from 104 to 90 ng/mg) and increased in the US group (from 95 to 145 ng/mg).(ABSTRACT TRUNCATED AT 250 WORDS)