Abstract: Objective To quantitatively evaluate the effects of dopamine (DA) and noradrenaline (NE) on renal medullary perfusion and the differences in perfusion in the outer and inner medulla using contrast-enhanced ultrasound. Methods and Results Contrast-enhanced ultrasound was performed in 10 dogs with simultaneous renal artery flow (RAF) measurement at the baseline level and during application of 3 different doses of DA and NE.During treatment with the 3 doses of DA,the changes of ultrasound-derived parameters (A,β and A*β) in the medulla were similar to the changes in the cortex.As compared with the baseline level,the ratios between the cortex and medulla exhibited no significant difference in A,β and A*β during DA treatment (P>0.05).No significant difference in ultrasound-derived medullar parameters was noted in dogs with NE treatment from the baseline level (P>0.05).However,a progressive decrease in the ratios of A,β and A*β between the cortex and medulla was noted during NE treatment in comparison with the baseline level (P<0.05).The velocity (β) and perfusion (A*β) of blood flow in the medulla decreased progressively from the outer medulla to the inner medulla at baseline (P<0.05),while the blood volume (A) remained unchanged (P<0.05). Conclusions The changes of blood flow in both the cortex and medulla are identical during DA treatment but different in the presence of NE.The progressive decrease in perfusion from the outer medulla to the inner medulla is attributed to the decrease in the velocity of blood flow.