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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]