Renal handling of free and conjugated catecholamines following surgical stress in the dog

Abstract

To investigate the renal handling of catecholamines (CA) during surgical stress, a renal balance between arterial influx (AI), renal venous outflow, urinary outflow, and tissue content of free and conjugated CA was established in 10 unilaterally nephrectomized female dogs. The stress of the surgery induced marked increases in arterial free norepinephrine + epinephrine (NE + E) and conjugated dopamine (DA). Free E and conjugated DA were cleared from the circulation by the kidney. Excretion, tissue uptake, and catabolism to homovanillic acid (the main metabolic pathway of DA sulfate in the dog) did not account for the gap between renal influx and outflow of conjugated DA. Tissue free DA increased during surgery. Free DA and free NE were not cleared from the circulation by the kidney, the excretion of free NE being very low. Five dogs had conjugated NE + E in the renal outflow in spite of its absence in AI and renal tissue during the surgery. Results demonstrated striking differences in the renal handling of free and conjugated DA, NE, and E, and suggest synthesis of free NE in the kidney during acute stress and its release into the circulation. Conjugation of endogenous NE + E was shown to occur in the kidney, and urinary CA excretion failed to reflect the sympathetic discharge in response to acute stress. Circulating conjugated DA may represent a source of free DA in the kidney and a precursor of free NE in peripheral sympathetic nervous tissue during acute stress.