Vascular compartmentalization of plasma norepinephrine in normal man: the relationships between venous and arterial norepinephrine concentration and the urinary excretion of norepinephrine.

To examine whether the concentration of NE in human plasma is dependent on the vascular source of the sample and to examine the contribution of the kidney to urinary NE, 14 normal men were studied. Plasma samples were obtained from a superficial forearm vein, and radial artery and urine samples were obtained during 1 hr of recumbency and 1 hr of upright posture. The Vne was greater than Ane during both recumbency and upright posture in black males. Such differences were not seen in age-matched white subjects. Stimulation of the sympathetic nervous system by upright posture increased both Vne and Ane in all subjects. NE concentrations in simultaneously obtained arterial and venous samples were different during the time of cardiovascular adjustments to upright posture. The urinary Xne increased after standing. Endogenous CCr decreased, whereas apparent NE clearance, calculated from the Ane, increased after standing, suggesting that a major portion of the augmented urinary Xne induced by upright posture was from an intrarenal source. We conclude that the concentration of NE in human blood is related to the specific vascular bed from which the sample is obtained, and that urinary NE is not solely derived from plasma by glomerular filtration but also arises from an unidentified renal source.