Effects of azotemia on renal extraction and clearance of PAH and TEA.

Dogs were made azotemic by bilateral ureteral-venous anastomosis. Subsequently, the left ureter, a systemic artery, and the left renal vein were cannulated. Left renal blood flow (RBF) was measured by an electromagnetic flowmeter. Left renal clearances and extractions of [14C]tetraethylammonium ([14C]TEA) and p-aminohippuric acid (PAH) were determined at five 40-min intervals after administraiton of loading doses and institution of a maintenance infusion containing PAH and [14C]TEA. The renal extraction of TEA was independent of blood urea nitrogen (BUN), whereas the extraction of PAH correlated inversely with BUN. Renal plasma flows calculated from urinary clearances and renal extractions agreed with renal plasma flows calculated from flowmeter data. The extraction of TEA remained constant over the 200-min experimental period, whereas the extraction of PAH increases progressively as a function of time. It is probable that those organic acids which accumulate in azotemia, and interfered with renal tubular secretion of PAH, were themselves eliminated after opening the ureteral-venous anastomosis. Thus, TEA is superior to PAH for evaluation of the renal circulation in azotemia.