Coronary heart disease and thus atherosclerosis is the leading cause of death among patients suffering from diabetes mellitus; men and women with diabetes have a three to fivefold higher coronary heart disease mortality or incidence rate compared with non-diabetic subjects [1]. Although a number of factors such as hyperglycaemia, dyslipidaemia, a procoagulant state, hyperinsulinaemia, glycation of proteins, oxidation or glycation of lipoproteins, as well as enhanced smooth muscle cell proliferation and foam cell formation, have all been suggested as possible links between diabetes and atherosclerosis [1], the increased risk of coronary heart disease among diabetic patients still remains largely unexplained.Hyperinsulinaemia could be directly involved in atherogenesis [2], although this possibility is fiercely debated [3][4][5][6]. In patients with insulin-dependent diabetes (IDDM) exogenous hyperinsulinaemia exists due to intermittent injections of large amounts of insulin [1], and in patients with non-insulin dependent diabetes (NIDDM) endogenous hyperinsulinaemia Diabetologia (1997) 40: 512-520 Effect of exogenous hyperinsulinaemia on atherogenesis in cholesterol-fed rabbits Summary To examine the hypothesis that hyperinsulinaemia promotes atherosclerosis, cholesterol-fed rabbits were injected subcutaneously with 6 IU of human insulin (n = 16) or placebo (n = 20) daily for 24 weeks; injection of insulin resulted in hyperinsulinaemia for up to 16 h after injection. Compared to placebo rabbits, insulin-treated rabbits had higher levels of insulin antibodies in plasma, similar levels of intermediate density, low density and high density lipoprotein cholesterol and similar activities of hepatic and lipoprotein lipase in post-heparin plasma, but lower levels of plasma C-peptide, blood glucose, postprandial plasma triglycerides, plasma cholesterol and very low density lipoprotein cholesterol. On univariate analysis, with and without adjustment for differences in plasma cholesterol levels between the two groups, there were no significant differences in extent or severity of atherosclerosis between insulin and placebo rabbits. Furthermore, after combining the results from all the rabbits to examine plasma insulin levels and the other variables mentioned above as predictors of atherosclerosis severity, plasma insulin level was not a predictor, on univariate or multiple linear regression analysis; the first ranked independent predictors were postprandial intermediate density lipoprotein cholesterol in the arch, and postprandial plasma triglyceride in both the thoracic and abdominal aorta. These results suggest that exogenous hyperinsulinaemia does not promote atherogenesis in cholesterol-fed rabbits, but that postprandial levels of intermediate density lipoprotein cholesterol or plasma triglycerides may be involved in atherogenesis. [Diabetologia (1997)