Novel use of ultrasound to examine regional blood flow in the mouse kidney

Conventional methods used for measuring regional renal blood flow, such as laser-Doppler flowmetry, are highly invasive, and each measurement is restricted to a discrete location. The aim of this study was to determine whether ultrasound imaging in conjunction with enhanced contrast agent (microbubbles; Vevo MicroMarker, VisualSonics) could provide a viable noninvasive alternative. This was achieved by determining changes in renal cortical and medullary rate of perfusion in response to a bolus injection of endothelin-1 (ET-1; 0.6, 1.0, or 2.0 nmol/kg) and comparing these responses to those observed in separate groups of mice with conventional laser-Doppler methods. Intravenous infusion of ET-1 in anesthetized male C57bl/6 mice resulted in a dose-dependent increase in mean arterial pressure and a dose-dependent decrease in total renal blood flow as measured by pulse-wave Doppler. ET-1 infusion resulted in a dose-dependent decrease in regional kidney perfusion as measured by both ultrasound with enhanced contrast agent and laser-Doppler measurements, verifying the use of ultrasound to measure regional kidney perfusion. Noted limitations of ultrasound imaging compared with laser-Doppler flowmetry included a lower degree of sensitivity to changes in tissue perfusion and the inability to assess rapid or transient changes in tissue perfusion. In conclusion, ultrasound represents an effective and noninvasive method for the measurement of relatively short-term, steadystate changes in regional blood flow in the mouse kidney.