Renal artery vasomotion: in vivo assessment in the pig with intravascular Doppler.

Intravascular Doppler is widely used for experimental studies in the coronary circulation. We designed this study to assess baseline bloodflow and arteriolar resistance in the porcine renal circulation and to study the vasomotor responses of vasoactive drugs. In anesthesized piglets (n = 15), renal arterial diameter was measured with quantitative angiography and blood flow velocity with a Doppler wire (Cardiometrics). Bloodflow and resistances were calculated at baseline and after injection of vasoactive drugs (isosorbide dinitrate, papaverine). This allowed us to determine the renal bloodflow reserve (the capacity of the kidney to augment basal bloodflow). Injection of isosorbide dinitrate was associated with an increase in average peak velocity of 64% (P < 0.01) and a small (from 4.5 to 4.74, P < 0.01) but significant increase in renal artery diameter, resulting in an increase in bloodflow of 82% (P < 0.01) and a decrease in arteriolar resistance of 46% (P < 0.01). Bloodflow returned to baseline (4.76 +/- 1.48 mL/s) approximately 5 min after isosorbide injection. Average Peak Velocity increased almost twofold after papaverine injection (60 +/- 10 to 108 +/- 24 cm/sec, P < 0.01). There was a significant (P < 0.01) increase in arterial bloodflow of 96% in the right and 79% in the left renal artery after injection of papaverine with a corresponding significant (P < 0.01) decrease in arteriolar resistance of 49% in the right and 44% in the left renal artery. Using a combination of quantitative angiography and intravascular Doppler allows easy measurement of baseline renal blood flow and of the effects of vasodilator drugs on bloodflow and resistance. The results show that a vasodilatator reserve exists in the renal circulation but is less marked than that reported in the coronary circulation.