Studies on the renal excretion of norepinephrine.

Studies were carried out in anesthetized dogs to investigate the renal clearance of norepinephrine (NE) and to determine the origin of this amine in the urine. Infused radioactive NE was cleared from plasma at a rate averaging 63.8% of the glomerular filtration rate. NE was shown to be freely filterable, and evidence has been presented which suggests but does not prove that the amine is partially reabsorbed from the glomerular filtrate; metabolism of NE in the tubular fluid by catechol-o-methyl transferase has not been excluded. The clearance of this catecholamine was not affected by changes in urine pH or flow. Total chronic denervation of one kidney was shown to have no effect on the rate of excretion of endogenous NE. Therefore, the NE that is excreted in the urine would appear to be solely derived from the catecholamines in circulating blood.