Serum uric acid levels and renal damage in hyperuricemic hypertensive patients treated with renin-angiotensin system blockers.

BACKGROUND: A correlation between hyperuricemia and renal target organ damage (TOD) was shown in hypertensive patients, locally mediated by the activation of renin-angiotensin system (RAS). We investigated whether high serum uric acid (UA) levels could negatively affect tubulointerstitial damage in hyperuricemic essential hypertensive patients with normal renal function, on treatment with RAS-blocking drugs. METHODS: We studied 40 patients with World Health Organization stage I-II essential hypertension, 9 with high serum UA levels (hyperuricemic group) and 31 with normal serum UA levels (normouricemic group, either normouricemics, n = 15, or formerly hyperuricemics in chronic allopurinol treatment, n = 16). All patients were on RAS-blocking drugs (either angiotensin-converting enzyme inhibitors or angiotensin II receptors blockers). Evaluation of renal TOD included urinary albumin excretion (UAE), Doppler ultrasound renal resistive index (RRI) and renal volume-to-resistive index ratio (RV/RRI) measurements. RESULTS: Hyperuricemics had significantly higher RRI and lower RV/RRI values than normouricemics. Creatinine clearance and UAE were similar between groups. Linear regression analysis showed that RV/RRI values were inversely related to serum UA levels (r = -0.57, P < 0.01). The logistic regression analysis selected serum UA as an independent predictor of decreased RV/RRI (odds ratio 4.45, 95% CI 1.47-13.45, P = 0.01). CONCLUSIONS: In hyperuricemic hypertensives normal serum UA levels are associated with normal RV/RRI, integrated marker of tubulointerstitial damage and renal arteriolopathy, independently of RAS activation.

Renal resistive index early detects chronic tubulointerstitial nephropathy in normo- and hypertensive patients.

BACKGROUND: We studied whether the measurement of intrarenal vascular resistance by Doppler ultrasonography, capable of investigating renal interstitial compartment, allows the early detection of chronic tubulointerstitial nephropathy (TIN). METHODS: 30 normotensive and 28 hypertensive (I-II OMS) patients with a clinical history suggestive of chronic TIN and normal renal function were enrolled. 40 healthy volunteers served as controls. Patients were considered TIN-negative or TIN-positive after investigating tubular function by urine concentrating and acidification tests. Renal sonographic parameters and renal resistive index (RRI) were obtained by duplex scanner. Glomerular filtration rate/effective renal plasmatic flow ratio was investigated by sequential renal scintigraphy in TIN-negative and TIN-positive patients; (99m)Tc-DMSA scintigraphy was also performed in TIN-positive patients. RESULTS: RRI values of TIN-positive normotensive and hypertensive patients were significantly higher (p < 0.01 for both) than those of TIN-negative patients and of controls. RRI values resulted to be linearly related to uricemia (r = 0.88, p < 0.0001) only in normotensive patients. RRI values also resulted to be linearly related to filtration ratio values (r = 0.60, p < 0.0001). (99m)Tc-DMSA scintigraphy confirmed interstitial renal damage (grade 1 and 2). CONCLUSION: RRI measurement allows the early identification of both normotensive and hypertensive patients with chronic TIN and signs of tubular dysfunction, when renal function is still preserved.