Objective:A large population of F2rats, obtained from a cross between male Lyon hypertensive (LH) rats and female Lyon normotensive (LN) rats, was studied in order to assess the relationship between increased body weight, hyperlipidaemia and high blood pressure which characterize LH rats.Methods:Mean arterial pressure (MAP) was recorded in male, conscious, freely moving LH, LN, F1and F2rats aged 30 weeks. Plasma total cholesterol, high-density lipoprotein-, low-density lipoprotein- and very low-density lipoprotein-cholesterol, phospholipids, triglycerides, insulin and glucose were measured.Results:In the F2cohort it was observed that high MAP was a recessive trait that depends on several genes and was unrelated to body weight. The left ventricular weight, corrected for tibia length, was correlated with MAP. Plasma total and high-density lipoprotein-cholesterol and phospholipids concentrations were lower in the F1rats than in the LN rats, suggesting an overdominance of the LN alleles. In the F2rats MAP was related to total, high-density lipoprotein- and low-density lipoprotein-cholesterol. Plasma triglycerides, insulin and the insulin: glucose ratio, which were higher in the LH rats than in the LN rats, were also correlated with MAP in the F2cohort. Using stepwise multiple regression analysis, MAP remained correlated with plasma total cholesterol, insulin and the insulin: glucose ratio, but not with triglycerides.Conclusions:Hypertension in LH rats is a recessive trait that is independent of body weight. In addition, the cosegregation of blood pressure with plasma cholesterol and, to a lesser degree, with insulin levels, which was observed in the present study provides the first direct evidence that these phenotypes are associated and are not due simply to genetic drift in the Lyon model.