The relationship of the renin-angiotensin system in type I diabetes to microvascular disease.

There are conflicting data on the relationship between diabetes mellitus and its complications and the renin-angiotensin-aldosterone system. Much of this relates to the patient populations studied (those with types I and II diabetes) and the definitions of diabetic complications. We studied plasma renin activity and concentration, and factors involved in their control (age, blood pressure, and sodium excretion) in 40 healthy subjects (group 1), 18 patients with type I diabetes without complications (group 2), and 31 with type I diabetes with proliferative retinopathy (group 3). The groups were well matched for age, sex, and body weight, but patients in group 3 had higher supine blood pressures than those in the other two groups (133/78 mm Hg vs 118/74 group 1, p less than 0.01; 120/72 group 2, p less than 0.05). Median plasma renin activity, both supine and erect, was 60 to 120% higher in group 3 than in group 1 (p less than 0.001) and 55 to 75% higher than in group 2 (p less than 0.05). There was good evidence of a fall in both values with increasing age in all three groups. Patients in groups 1 and 2 showed evidence of inverse relationships of both blood pressure and urinary sodium with plasma renin activity/concentration ratio, but these relationships were not apparent in subjects in group 3. There is thus evidence of impaired regulation of renin secretion in persons with type I diabetes with proliferative retinopathy, the commonest form of microvascular disease. This may contribute to the relative hypertension and progression of complications.