Renal functional reserve and renal hemodynamics in hypertensive patients

The renal functional reserve (RFR) is the ability of the kidneys to increase renal plasma flow and glomerular filtration rate (GFR) in response to protein intake. It is a measure of functional and anatomic integrity of nephrons. It is not known what relation between RFR and kidney Doppler parameters. We aimed to study the relation between the RFR and renal hemodynamic parameters in hypertensive patients with and without nephropathy who had normal kidney function. Twenty-four hypertensive subjects with nephropathy (HTN-n, n = 10) and hypertension without nephropathy (HTN, n = 14) were included in the study. Control group included 11 healthy subjects. Baseline GFR (GFR1) and GFR after intake of egg protein 1 mg/kg of body weight were determined (GFR2). RFR was calculated by the following formula: (GFR2-GFR1)/GFR1 × 100%. Doppler ultrasonography was performed. Arterial blood pressure (BP), body mass index (BMI), and estimated GFR were also recorded. HTN and HTN-n groups had impaired levels of RFR compared with controls (p < 0.05), significantly decreased value of flow velocity parameters (Vmax, Vmin), and increased RRI compared with controls. There was significant negative correlation of RFR with blood pressure levels (sBP, r = -0.435, p = 0.009; dBP, r = -0.504, p = 0.002), RRI (r = -0.456, p = 0.008), micro albuminuria (MAU, r = -0.366, p = 0.031) and positive correlation with Vmax and Vmin (r = 0.556, p = 0.001 and r = 0.643, respectively, p < 0.001). Linear regression showed that RRI and MAU were independent predictors of decreased RFR. RFR is lower in hypertensive patients despite near-normal level of kidney function and is related to particular level of BP. RRI and MAU were independent predictors of decreased RFR.