The influence of dihydralazine and angiotensin-II blockade on renal extraction of [131I]hippuran.

The renal extraction of [131I]ortho-iodohippuran ([131I]OIH) was measured during the first minutes after the bolus injection during renal vein catheterization of two groups of hypertensive patients. Concomitantly the hippuran clearance (effective renal plasma flow (ERPF) was determined with a quantitative renographic technique based on net kidney uptake between 1 1/2 and 2 1/2 min and plasma radioactivity 2 min after the bolus injection of hippuran. The study was repeated 30 min after intravenous administration of dihydralazine (0.1 mg/kg body weight) in 14 subjects (group A) and during continuous infusion of the angiotensin II blocking agent Saralasin (5 micrograms/kg . min) in 10 subjects (group B). Before dihydralazine was given, the rate of [131I]OIH extraction was (Mean +/- S.D.) 74.0 +/- 16.7% in the 2 min sample after bolus injection of hippuran, 67.5 +/- 17.3% after 10 min, falling to 53.0 +/- 15.3% after 30 min. There was no difference after dihydralazine administration, as the extraction values were 75.6 +/- 17.5 and 65.6 +/- 21.4% 2 and 10 min after the bolus injection of hippuran. The extraction values before Saralasin infusion were 74.2 +/- 15.7%, 59.8 +/- 18.2% and 47.1 +/- 16.6% at 2, 10 and 25 min after bolus injection of hippuran. Saralasin elicited no change in the extraction, as the values were 74.1 +/- 18.6% and 64.3 +/- 23.2%, 2 and 10 min after hippuran injection. For kidneys with ERPF above 100 ml/min . 1.73 m2 the extraction 2 min after hippuran injection was at the level of 82%, whereas the extraction fell rapidly with further reduction in ERPF. It is concluded that ERPF determined with the renographic technique, reflects the renal plasma flow when the clearance for the individual kidney exceeds 100 ml/min . 1.73 m2. This is the case also after dihydralazine and Saralasin administration.