Angiotensin converting enzyme inhibition worsens the excretory phase of diuretic renography for obstructive hydronephrosis

Purpose: A growing body of evidence identifies the renin-angiotensin system as a key factor in the onset and progression of renal damage in chronic pa rtial obstruction, which often represents a complex diagnostic challenge. A prospective study was undertaken to evaluate the role of captopril mercapt oacetyltriglycine-3 (MAG-3) renography as an early diagnostic test of obstr uction. We report the results in a subgroup of children who underwent surgi cal correction for pyeloureteral obstruction. Materials and Methods: Pyeloplasty was performed in 12 patients, including 10 males, 2 to 72 months old (median age 7) with unilateral hydronephrosis, including normal renal function and blood pressure. Basal and captopril en hanced diuretic renography with (99m)technetium MAG-3 was performed within 24 hours using the same hydration and diuretic stimulus (0.75 mg./kg. furos emide), and 0.75 mg./kg. captopril was administered orally 60 to 90 minutes before scintigraphy. Results: No adverse effects or modifications of the blood pressure were obs erved after captopril administration. The diuretic response was deeply wors ened by angiotensin converting enzyme inhibition in each hydronephrotic kid ney even when the basal study was only slightly abnormal (15-minute washout basal -27 +/- 16%, after captopril -9 +/- 13, p <0.005). After surgical co rrection the diuretic washout during angiotensin inhibition appeared normal in all patients (15-minute washout -56 +/- 14%). Separate renal function a nd parenchymal transit of MAG-3 were not modified by angiotensin converting enzyme inhibition, preoperatively or postoperatively. Conclusions: Our data confirm the influence of angiotensin on the kidney ex cretory system in human hydronephrosis and suggest a role for captopril enh anced diuretic renography in the early diagnosis of pyeloureteral obstructi on. Further work is needed to evaluate angiotensin converting enzyme inhibi tion as a protective agent in obstructive nephropathy.