Renal handling of norepinephrine and epinephrine in the pig

To investigate the renal handling of catecholamines in the pig, intravenous infusions of 51Cr-EDTA and PAH were performed in 7 animals, and samples for simultaneous measurement of norepinephrine (NE), epinephrine (E), 51Cr-EDTA and PAH were obtained through catheters placed into the aorta, left renal vein and both urethers. For both kidneys together, 51Cr-EDTA clearance [GFR] averaged 48 +/- 14 (+/- SD) ml/min (2.23 +/- 0.66 ml/kg/min). In the left kidney, GFR averaged 22 +/- 9 ml/min, arteriovenous PAH extraction 0.87 +/- 0.09, and calculated total renal plasma flow 91 +/- 30 ml/min. Plasma NE and E were lower in renal venous than arterial blood (P less than 0.005), extraction ratios averaging 0.36 and 0.77, respectively. NE excretion rate in final urine (8.9 +/- 4.3 ng/min) exceeded transrenal NE extraction rate (5.2 +/- 3.9 ng/min) by 3.7 +/- 4.4 ng/min. In contrast, urinary E excretion rate (2.9 +/- 2.0 ng/min) was slightly lower than transrenal E extraction rate (3.6 +/- 3.8 ng/min). These observations suggest that in pig kidneys, plasma PAH extraction rate and GFR related to body weight are quite similar to values in man. Three quarters of circulating E are extracted for the most part by tubular secretion, and the slightly smaller amount appearing in urine is consistent with some intrarenal metabolism. NE, presumably originating from intrarenal neuronal release and/or de novo production, is secreted into the urine.