DRUG-INDUCED CHANGES IN RENAL HIPPURATE CLEARANCE AS A MEASURE OF RENAL BLOOD-FLOW

We studied the accuracy of the plasma I-131-hippurate clearance techni que to monitor drug-induced changes in renal blood flow (RBF) by compa ring it to a flow probe technique in six conscious, chronically instru mented dogs. Placebo caused no change in RBF, either established by hi ppurate clearance (ERPF(hip)) or by renal blood flow probe (RBF(probe) ). Enalaprilate induced a rise in ERPF(hip) and RBF(probe) (+26 +/- an d 44 +/- 12%), as did dopamine (+16 +/- 4 and +33 +/- 5%). Intravenous infusion of norepinephrine induced a rise in ERPF(hip) (+2 +/- 6%, NS ) and in RBF(probe) (+18 +/- 3%), as did nitroprusside (+14 +/- 4% and +13 +/- 6%, NS). Indomethacin induced a fall in ERPF(hip) (-8 +/- 2%) and in RBF(probe) (-7 +/- 3%, NS), as did angiotensin II (-19 +/- 1 a nd -26 +/- 3%). Renal hippurate extraction (E(hip)) was affected by en alaprilate, dopamine, and angiotensin II (-5 +/- -7 +/- 1, and +5 +/- 2%, respectively). Hematocrit (Hct) was affected by dopamine, norepine phrine, and nitroprusside (+2 +/- 1, +6 +/- 1, and -5 +/- 2%, respecti vely). Drug-induced changes in ERPF(hip) correlated well with changes in RBF(probe) (r = 0.902, P < 0.01). Changes in E(hip) did not indepen dently affect this relation, whereas changes in Hct did: Delta RBF(% o f baseline) = 1.529 x Delta ERPF(hip)(% of baseline) + 1.296 x Delta H ct(% of baseline). These data indicate that drug-induced changes in pl asma hippurate clearance can, even when changes in renal hippurate ext raction are unknown, be used as a reliable indicator of changes in ren al blood flow if changes in hematocrit are taken into account.