Renal Ultrafiltration Changes Induced by Focused US

Purpose: To determine if focused ultrasonography (US) combined with a diagnostic microbubble-based US contrast agent can be used to modulate glomerular ultrafiltration and size selectivity. Materials and Methods: The experiments were approved by the animal care committee. The left kidney of 17 healthy rabbits was sonicated by using a 260-kHz focused US transducer in the presence of a microbubble-based US contrast agent. The right kidney served as the control. Three acoustic power levels were applied: 0.4 W (six rabbits), 0.9 W (six rabbits), and 1.7 W (five rabbits). Three rabbits were not treated with focused US and served as control animals. The authors evaluated changes in glomerular size selectivity by measuring the clearance ratesof 3000- and 70 000-Da fluorescence-neutral dextrans. The creatinine clearancewas calculated for estimation of the glomerular filtration rate. The urinary protein-creatinine ratiowas monitored during the experiments. The authors assessed tubular function by evaluating the fractional sodium excretion, tubular reabsorption of phosphate, and -glutamyltransferase‐ creatinineratio. Whole-kidney histologic analysis was performed. For each measurement, the values obtained before and after sonication were compared by using the paired t test. Results: Significant (P .05) increases in the relative (ratio of treated kidney value/nontreated kidney value) clearanceof small- and large-molecule agents and the urine flow ratesthat resulted from the focused US treatments were observed. Overall, 1.23-, 1.23-, 1.61-, and 1.47-fold enhancement of creatinine clearance, 3000-Da dextran clearance, 70 000-Da dextran clearance, and urine flow rate, respectively, were observed. Focal tubular hemorrhage and transient functional tubular alterations were observed at only the highest (1.7-W) acoustic power level tested.