Measurement of regional kidney perfusion in mice: comparison of a novel, non‐invasive technique against conventional laser‐Doppler flowmetry.

Laser‐Doppler (LD) flowmetry is the most well accepted method to assess regional kidney perfusion. Limitations include invasiveness and a very discrete (~ 1 mm 3 ) area of measurement. The aim of this study was to compare regional kidney blood flow responses to endothelin‐1 (ET‐1) in male C57BL/6 mice obtained with LD methodology to those obtained using ultrasound (US) imaging with enhanced contrast agent (Vevo MicroMarker, VisualSonics). Renal cortical (CBF) and outer medullary perfusion (MBF) responses to ET‐1 were determined in isoflurane anesthetized mice using acutely implanted LD probes (implanted 1 mm and 3 mm respectively via retroperitoneal exposure of the left kidney) or by US imaging in separate groups of mice. Regional blood flow was determined using US by multiplying contrast agent volume and velocity in a user defined region of interest. Mice received a single i.v. injection of saline or ET‐1 (0.6, 1 or 2 nmol/kg) and responses were calculated 20 min post‐injection as % change from baseline values. ET‐1 reduced both CBF and MBF as measured by LD and by US. The pattern of responses was similar between techniques, although the magnitude of responses was larger with US. Total renal blood flow was also measured by pulse‐wave Doppler. The % changes in renal blood flow in response to increasing doses of ET‐1 were proportional to changes in regional blood flow (‐1±4, ‐22±8, ‐60±6, respectively). These data indicate that US imaging with enhanced contrast agent represents a viable, non‐invasive alternative to LD for assessing regional kidney blood flow responses in mice.