Isolated perfused rat kidneys rapidly excreted unchanged epinephrine and nonepinephrine into the urine. Their metabolites accumulate both in the recirculating medium and in the urine. The fractional excretion of 3H epinephrine and 3H norepinephrine is 4.3 ± 0.4 and 2.5 ± 0.1, respectively, and their clearance is directly related to the glomerular filtration rate. No maximum tubular transport was observed even at very high perfusion medium concentrations. Renal metabolite degradation of epinephrine was significantly higher than that of norepinephrine during an average of 25 min of perfusion (29 ± 4% vs 15 ± 2%). Increased conversion of 3H epinephrine to 3H metanephrine accounted for this difference, conversion of 3H norepinephrine to 3H normethanephrine being comparatively small (22 ± 3% vs 8.3 ± 1.6%). Conversion to 3H vanillylmandelic acid was identical in both cases. Catechol acids were almost unmeasurable and conjugation did not occur. The rat kidney actively secretes epinephrine and norepinephrine in direct proportion to its plasma concentration and glomerular filtration rate. The kidney extracts approximately 2%/min of 3H epinephrine from the medium, 41% excreted unchanged. By contrast only 1.4%/min of 3H norepinephrine is extracted 59% excreted unchanged. These studies imply that measurement of free catecholamine excretion accurately reflects plasma catecholamine levels. Interpretation of urinary catecholamine excretion in different pathophysiologic states should take into account simultaneous changes in renal function as well as the fact that the kidney excretes and metabolizes epinephrine and norepinephrine at different rates.
|Original language||English (US)|
|State||Published - Jan 1 1975|
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