Effects of endothelin-1 on renal microvasculature measured using quantitative ultrasound.

Renal vascular resistance is an important feature of kidney function and disease. To maintain adequate blood flow, renal vascular resistance varies in response to changes in systemic pressure. Vascular resistance is largely determined by arteriolar diameter, which is regulated by local and systemic factors. We used quantitative ultrasound techniques to follow renal vascular changes in anesthetized dogs during local intraarterial infusion of a potent vasoconstrictor, endothelin-1 (ET-1). Average arteriolar diameters were estimated by analyzing echo-signal spectra (5-15 MHz) obtained from renal cortex in vivo before, during, and after ET-1 infusion. At calculated arterial concentrations of 0.01 nM, 0.1 nM, and 1.0 nM, ET-1 reduced the average arteriolar diameter of 38 +/- 2 microns by 2%, 63%, and 91%, respectively, without producing a significant change in systemic blood pressure. Changes in scatterer size were consistent with the observed changes in renal hemodynamics detected using Doppler techniques. In addition, acoustic attenuation was found to increase with ET-1 concentration. These data suggest that quantitative ultrasound methods are sensitive to changes in renal arteriolar diameter, and may be a new noninvasive method for continuously monitoring changes in vascular resistance.