Diabetes and plasma lipoproteins in Native Americans. Studies of the Pima Indians.

OBJECTIVE--To determine the effects of diabetes on plasma lipoproteins in Pima Indians, to identify metabolic determinants of these differences, and to examine the effects of various modes of diabetes therapy. RESEARCH DESIGN AND METHODS--A series of studies was performed including a population survey of lipoprotein concentrations, kinetic studies of VLDL and LDL metabolism, and studies of the effects of weight loss, sulfonylureas, and high carbohydrate diets. RESULTS--Population data established that diabetes was consistently associated with elevations in total and VLDL TGs and decreases in HDL cholesterol. Metabolic studies indicated multiple alterations in VLDL metabolism induced by NIDDM, including overproduction of VLDL TG, impaired clearance of VLDL TG and apoB, and decreases in adipose tissue lipoprotein lipase. Although changes in LDL concentrations accompanying NIDDM were minimal, the clearance of LDL appeared to be impaired and a higher proportion of VLDL was metabolized without conversion to LDL. There were significant changes in the flux of particles to the LDL compartment. Total and VLDL TG concentrations were found to be inversely related to rates of insulin-mediated glucose disposal, and HDL cholesterol concentrations were positively related to glucose disposal. These relationships between lipoproteins and insulin action were independent of adiposity and insulin, suggesting that insulin resistance may be involved with diabetes-induced changes in VLDL and HDL. Weight loss was associated with decreases in total and VLDL TG, decreases in total and LDL cholesterol, and improvements in the ratio of HDL to LDL cholesterol. Sulfonylurea therapy was associated with lower total and VLDL TGs and lower LDL cholesterol, but little change in HDL. Substitution of complex carbohydrates for saturated fat in the diet showed consistent and significant decreases in total and LDL cholesterol, no decreases in HDL cholesterol, or elevation of total or VLDL TG. CONCLUSIONS--Studies suggest that there are multiple changes in plasma lipoproteins accompanying NIDDM in Pima Indians, but that many of these may be reversed by current modes of hypoglycemic therapy.