Decreased mitogenic activity in hypercholesterolaemic plasma

. The mitogenic activity on rat aortic smooth muscle cells of plasma from patients with hypercholesterolaemia was compared to that of plasma from a normocholesterolaemic control group and to that obtained after lowering plasma cholesterol levels in the hypercholesterolaemic groups with simvastatin. Mean plasma total and low density lipoprotein cholesterol and apolipoprotein B concentrations in the two groups were 8.62 ± 0.62 mmol l −1 , 7.03 ± 0.56 mmol l −1 and 1.96 ± 0.14 g l −1 , respectively, and 5.05 ± 0.20 mmol l −1 , 3.42 ± 0.18 mmol l −1 and 0.80 ± 0.04 g l −1 , respectively, all differences significant at P < 0.001. During simvastatin treatment these parameters decreased to 5.70 ± 0.35, 4.15 ± 0.33 mmol l −1 and 1.33 ± 0.08 g l −1 , all changes being significantly ( P < 0.001) lower than before treatment. Hyperlipidaemic plasma in untreated patients had a significantly lower mitogenic activity than normolipidaemic control plasma as measured by autoradiographic labelling of DNA after 3 H‐thymidine incorporation, 25.7 ± 1.8% vs. 32.0 ± 1.9%, P < 0.05. Lowering plasma cholesterol levels in the hyperlipidaemic patients ‘normalized’ the mitogenic activity to 32.3 ± 1.6%, P < 0.05. The reason for this unexpected finding is not known.