SOURCES OF HUMAN URINARY EPINEPHRINE

The kidney is a likely sourer for some urinary epinephrine (E) since a drenalectomized animals and humans continue to excrete urinary E and t he human kidney contains E synthesizing enzymes. We studied subjects d uring an intravenous infusion of H-3-E tu determine the fraction of ur inary E derived from the kidney. Eight normal subjects (CON) and 5 old er, heavier hypertensives (OHH) ate a light breakfast along with ascor bic acid supplementation and had intravenous and arterial lines placed . They received an infusion of H-3-E and had an oral water load. Durin g the final hour of H-3-E infusion. urine and arterial blood samples w ere collected for H-3-E and E levels. After the H-3-E infusion was abr uptly discontinued, arterial blood samples were collected to measure H -3-E kinetics. The total body clearance of H-3-E was about 2,500 ml/mi n from plasma and clearance of H-3-E to urine was about 170 ml/min. CO N had plasma E levels of 43 +/- 4 pg/ml. Their predicted rate of clear ance of E from plasma to urine of 7,471 +/- 865 pg/min was less than ( P = 0.018) the actual urinary E excretion of 15,037 +/- 2,625 pg/min. Thus, 43 +/- 9% of urinary E in CON was apparently derived from renal sources and not filtered from blood. Among OHH 85 +/- 4% of urinary E was derived from the kidney, significantly (P < 0.01) different from C ON. The OHH also produced much more urinary E than predicted from plas ma H-3-E clearance into urine (P = 0.03). A major fraction of urinary E is not filtered from the blood stream but is apparently derived from the kidney. A small fraction of urinary E may be derived from E store d in nerve endings along with norepinephrine. but this probably repres ents less than 2% of urinary E. Renal cleavage of E sulfate into E may be another potential source of urinary E. Some, and perhaps most, uri nary E not filtered from the bloodstream is derived from renal N-methy lation of norepinephrine as thr human kidney has two enzymes capable o f converting norepinephrine to E. In conclusion, a major portion of ur inary E is derived from the kidney and not filtered from the bloodstre am. This is an important factor in the interpretation of urine E level s. Renal E could alter renal blood Bow, electrolyte reabsorption, and renin release prior to excretion into urine.