Renal handling of dopa, dopamine, norepinephrine, and epinephrine in the dog

The uptake and excretion of endogenous dopa, dopamine, norepinephrine, and epinephrine by the kidney were studied. Blood samples were taken from the aorta at the origin of the renal artery and from the renal vein during a timed urine collection in each of six anesthetised greyhound dogs. Arterial plasma dopa (1,043 +/- 129 pg/ml) and epinephrine (218 +/- 96 pg/ml) were consistently higher than venous levels of dopa (591 +/- 80) and epinephrine (54 +/- 16 pg/ml), showing extraction of these by the kidney, whereas arterial plasma norepinephrine (329 +/- 89 pg/ml) and dopamine (64 +/- 9 pg/ml) were lower than the venous levels of norepinephrine (695 +/- 161 pg/ml) and dopamine (239 +/- 45 pg/ml), indicating secretion of these catecholamines into the circulation. The dopa extracted did not appear in the urine. Norepinephrine (7.2 +/- 1.7 ng/min), epinephrine (4.5 +/- 1.7 ng/min), and dopamine (3.2 +/- 0.7 ng/min) were excreted in the urine. These rates of urinary excretion could be accounted for by glomerular filtration and tubular secretion of the three catecholamines. The kidney extracts circulating dopa. It extracts and excretes epinephrine, norepinephrine, and dopamine, and, in addition, secretes both dopamine and norepinephrine into the circulation. These observations emphasize the important relationship between renal function and the peripheral sympathetic nervous system.