Blood Pressure Changes and Renal Function in Incipient and Overt Diabetic Nephropathy

Four studies are included in this report on the relationship of blood pressure, protein excretion, and renal hemodynamics, where renal function was measured by 125I-iothalamate clearance and 131I-hippuran clearance, and urinary albumin excretion was measured by radioimmunoassay. The first concerns the relationship between blood pressure and renal function in a cross-sectional study of 56 patients with type I diabetes with various degrees of renal involvement. In the second, multiple regression analysis was used in a prospective study of diabetic nephropathy in patients with type I diabetes. Inclusion criteria were age at diagnosis less than 20 years, initial diabetes duration 3 to 20 years, and follow-up period more than 7 years. Urinary albumin was less than 70 micrograms/min, and glomerular filtration rate, renal plasma flow, and urinary albumin were measured in all patients. The third was a long-term follow-up study of persons with type I diabetes, with special reference to development of changes in urinary albumin, glomerular filtration rate, and blood pressure. Diabetes duration in this study was 7 to 20 years. Finally, a prospective study was conducted on clinical proteinuria and mortality in patients with type II diabetes, with special reference to initial urinary albumin and blood pressure. A close association was established among all variables measured in the cross-sectional study. On multiple regression analysis as well as in the long-term follow-up study, it appeared that both elevated urinary albumin (greater than 15 micrograms/min at baseline) and high glomerular filtration rate (greater than 150 ml/min) are major determinants for subsequent progression to nephropathy. In patients with type II disease, increase in urinary albumin is a strong predictor for development of proteinuria and early mortality. High blood pressure seems not to be a major determinant in these patients, but further studies are required.