The renin angiotensin system in diabetes mellitus. A physiological and therapeutic study

The purpose of this study was to measure components of the renin angiotensin system in patients with type 1 diabetes mellitus, with and without nephropathy, to study the renal sensitivity to angiotensin II in uncomplicated type 1 diabetes and to investigate the short and long-term renal effects of angiotensin II reduction with angiotensin converting enzyme inhibitors in patients with diabetic nephropathy. In patients with type 1 diabetes without complications, plasma renin activity, angiotensin II and aldosterone levels were normal. In patients with diabetic nephropathy, renin levels were elevated, probably partly as a result of diuretic treatment. However, renin levels were also elevated compared to patients with other renal diseases who had similar treatment and degree of azotemia. The renal sensitivity to angiotensin II was normal in patients with uncomplicated diabetes. The reduction in glomerular filtration rate and renal plasma flow and increases in filtration fraction during A II infusion were equal to those in healthy controls. Nine days' captopril treatment in 15 patients with diabetic nephropathy induced an increase in renal plasma flow and a decrease in filtration fraction. The glomerular filtration rate remained unchanged. During 8 weeks' randomised enalapril or metoprolol treatment in 40 patients with diabetic nephropathy, enalapril treatment reduced proteinuria to half the initial value. Metoprolol treatment had no effect on proteinuria. Furosemide was also used and the dosage was adjusted to give equally effective blood-pressure control in both groups. During long-term treatment with captopril in patients with diabetic nephropathy, the rate of decline in kidney function over time was reduced to one-fourth the initial value even though the blood pressure was only slightly reduced. The renin angiotensin system appears to be functionally intact in diabetes mellitus and interruption by ACE inhibition reduces proteinuria both by blood pressure reduction and by an effect independent of systemic blood pressure. Long-term treatment might protect kidney function in diabetic nephropathy to a greater extent than would be expected from the blood-pressure-lowering effect alone.