The relationship between active renin concentration and plasma renin activity in Type 1 diabetes

Aims Circulating activity of the renin-angiotensin-aldosterone system (RAAS ) can be assessed by measuring plasma active renin concentration (ARE), as well as by measuring plasma renin activity (PRA). We aimed to assess the re lationships between ARE and PRA in Type 1 diabetic compared with non-diabet ic control subjects. We also assessed concentrations of the active renin pr ecursor, prorenin. Patients and methods Thirty-five Type 1 diabetic subjects and 34 non-diabet ic control subjects were assessed. Groups had similar ages, sex distributio ns, body mass indices, systolic and diastolic blood pressures. PRA was meas ured by radioimmunoassay of angiotensin I generation from endogenous substr ate. ARE and total renin concentration (TRE) were measured by immunoradiome tric assay (Nichols Institute Diagnostics, USA). Prorenin concentration was calculated as the difference between ARE and TRE. Results PRA was significantly lower in Type 1 diabetic than in control subj ects (0.8 (0.4-1.1) vs. 1.1 (0.9-1.9) pmol/ml per h; P < 0.005), while ARE was similar (17 (9-33) vs. 18 (15-25) mU/l; P = 0.548). PRA (log(e) transfo rmed) correlated strongly with ARE in diabetic (r = 0.49; P = 0.003) and co ntrol subjects (r = 0.59; P = 0.0002), but there was significant vertical s eparation of the regression lines for the two groups (P < 0.0001). Prorenin concentrations were significantly higher in Type 1 diabetic subjects (249 (170-339) vs. 171 (153-219) mU/l; P = 0.005). Diabetic subjects with high p rorenin concentrations (> 400 mU/l (control mean + 3 sd)) were more likely to have microalbuminuria (P = 0.027) and peripheral neuropathy (P = 0.049). Conclusions Type 1 diabetes is associated with an altered relationship betw een ARE and PRA, such that ARE is higher for a given PRA compared with non- diabetic control subjects. Both ARE and PRA are used to assess circulating RAAS activity. The altered relationship between the two in Type 1 diabetic subjects suggests that neither parameter alone is necessarily an adequate a nd reliable index of such activity. Higher prorenin concentrations, particu larly in association with microvascular complications, were confirmed in th e Type 1 diabetic subjects.