Duplex sonographic registration of age and diabetes-related loss of renal vasodilatory response to nitroglycerine

Background. Nitroglycerine effects dilatation of the vas afferens in the ki dney by its active metabolite nitric oxide (NO). In diabetic nephropathy, N O appears to cause hyperfiltration and proteinuria. The aim of this study w as to investigate the potential of duplex Doppler ultrasonography in record ing changes in resistive indices following nitroglycerine and whether the e xtent of changes in diabetic nephropathy is reduced as a result of the arte riolar dilatation mediated by NO. Methods. Fifty-three subjects made up three groups: group 1, 12 young healt hy volunteers (5 male, 7 female, 28+/-6 years); group 2, 21 older healthy v olunteers (7 male, 14 female, 62+/-8 years); group 3, 20 patients (13 male, 7 female, 56+/-18 years) with mild diabetic nephropathy. The resistive ind ex (RI) was measured in the interlobar arteries before, and 1, 3 and 5 min after administration of 0.8 mg sublingual nitroglycerine. Results. The initial RI of 0.592 decreased in group 1 by 10.8% (P<0.01) aft er nitroglycerine, in group 2 the initial figure of 0.631 decreased by 5.9% (P<0.01), and in group 3 the initial figure of 0.669 decreased by 3.4% (P< 0.01). Initial RI values differed significantly between groups 1 and 3 (P<0 .01) and groups 1 and 2 (P<0.01), as did values between all healthy volunte ers (groups 1 and 2, n=33) and patients with nephropathy (P<0.005). The ext ent of Delta RI differed significantly between groups 1 and 3 (P<0.01), 1 a nd 2 (P<0.02), and between all volunteers and group 3 (P<0.003). In groups 1 and 2 the initial RI was dependent on age (P<0.03), in group 3 on age and creatinine clearance (P<0.02 and P<0.05 respectively). Delta RI correlated with age in the healthy subjects (P<0.01) and with duration of diabetes in diabetic nephropathy (P<0.03). Conclusions. Haemodynamic changes in renal perfusion caused by nitroglyceri ne can be detected using duplex ultrasonography. In healthy subjects, Delta RI declines with increasing age. In diabetic nephropathy patients, the res ponse to nitroglycerine is reduced. The increased initial RI in such patien ts suggests fixed arteriolar damage.