• ureteric obstruction;
  • Doppler ultrasonography;
  • resistive index;
  • diuretics;
  • radio-contrast agents

Objective  To compare the effects of diuresis induced by a loop diuretic (frusemide), an osmotic diuretic (mannitol) and a high-osmolar radio-contrast medium (sodium iothalamate) on the intrarenal resistive index (RI) in dogs with chronic unilateral partial ureteric obstruction (UPUO).

Materials and methods  The split renal clearance and intrarenal RI were estimated in 11 dogs with chronic UPUO. Doppler ultrasonography measurements of the interlobar arteries were obtained before and 10 min after the intravenous infusion of 1 mg/kg frusemide, 1 g/kg mannitol or 20 mL 60% sodium iothalamate. The same experimental protocol was repeated with another drug at 1-week intervals.

Results  There was a significant difference between the intrarenal RI of obstructed and unobstructed kidneys in the chronic phase of UPUO. While mannitol and sodium iothalamate significantly increased the RI in both kidneys, differences in RI between the kidneys decreased after infusing the two drugs. However, while frusemide insignificantly increased the RI in the obstructed kidney, it decreased the RI in unobstructed one. Consequently, the difference in RI between the kidneys increased significantly after administering frusemide. There were no significant differences in urinary volume after administering each of the drugs.

Conclusions  As there were no significant differences in the diuretic effects of the drugs, frusemide may have additional effects on the RI of unobstructed kidneys other than diuresis. Frusemide increased the difference between the intrarenal RI of the kidneys and therefore may improve the detection of unilateral urinary obstruction in humans.