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Introduction: The measurement of renal functional reserve (RFR) can unmask glomerular hyperfiltration in residual nephrons, but its determination is time-consuming. In this study, we assessed whether contrast-enhanced ultrasound (CEUS) is a valuable alternative to the gold standard inulin clearance and whether L-arginine or protein shakes lead to similar changes in glomerular filtration rate (GFR) as animal proteins in men and women. Methods: Changes in GFR and renal microperfusion were studied in 25 healthy subjects (8 men, 17 women) by simultaneously performing inulin clearance and CEUS (perfusion index, PI) before and 1 and 2 h after different protein loads (L-arginine, protein shake or meat). The Doppler parameters – renal resistive index (RRI) and pulsatility index (PuI) – were also measured. Results: None of the oral protein loads induced significant changes in CEUS-assessed PI. Only meat increased inulin clearance (from 111.2 ± 16.0 to 149.8 ± 27.2 mL/min, p < 0.05) and mobilized RFR, while L-arginine decreased GFR (106.7 ± 45.3 to 86.3 ± 42.6 mL/min, p < 0.05). Protein shakes had a neutral effect. There were no correlations between changes in inulin clearance and PI. At Doppler, RRI and PuI increased after meat intake (from 0.647 ± 0.029 to 0.694 ± 0.050 a.u., p < 0.05 and from 1.130 ± 0.087 to 1.318 ± 0.163 a.u., p < 0.05, respectively), but their changes also did not correlate with changes in inulin clearance. Results were similar in both sexes. Conclusions: CEUS is not a valuable alternative for inulin clearance to measure RFR. Meat ingestion leads to modest changes in renal Doppler parameters and to glomerular hyperfiltration in both women and men, while protein shakes and L-arginine do not. [ABSTRACT FROM AUTHOR]

Background Disturbances in renal microcirculation play an important role in the pathophysiology of chronic kidney disease (CKD), but the lack of easy accessible techniques hampers our understanding of the regulation of the renal microcirculation in humans. We assessed whether contrast-enhanced ultrasound (CEUS) can identify differences in cortical perfusion and alterations induced by different dietary salt intakes in CKD patients and controls. Methods Participants underwent CEUS twice: once after 5 days of high-salt (HS) intake, and again after 5 days of low salt (LS) diet. Sonovue® (0.015 mL/kg/min) was perfused as contrast agent and four consecutive destruction–reperfusion sequences were analysed per visit. The primary outcome measure was the (change in) mean perfusion index (PI) of the renal cortex. Results Forty healthy volunteers (mean age ± standard deviation 50 ± 8 years) and 18 CKD Stages 2–4 patients [aged 55 ± 11 years, estimated glomerular filtration rate (eGFR) 54 ± 28 mL/min/1.73 m2] were included and underwent CEUS without side effects. Under HS conditions, cortical PI was significantly lower in CKD patients [1618 ± 1352 versus 3176 ± 2278 arbitrary units (a.u) in controls, P = 0.034]. Under LS, renal PI increased in CKD patients (with +1098 to 2716 ± 1540 a.u. P = 0.048), whereas PI remained stable in controls. In the continuous analysis, PI correlated with eGFR (Spearman's r  = 0.54, P = 0.005) but not with age, sex, blood pressure or aldosterone levels. Conclusions CEUS identified important reductions in cortical micro-perfusion in patients with moderate CKD. Lowering salt intake increased perfusion in CKD patients, but not in controls, underlining the benefits of an LS diet in CKD patients. Whether a low PI is an early sign of kidney damage and predicts renal function decline needs further study. [ABSTRACT FROM AUTHOR]