CORRELATES OF URINARY-EXCRETION OF CATECHOLS IN HUMANS

An endogenous system involving renal uptake of dihydroxyphenylalanine (DOPA) and conversion to the natriuretic catecholamine, dopamine (DA), may participate in sodium homeostasis. Normal values for and correlat es of urinary excretion of free (unconjugated) catechols in humans are incompletely understood. Daily excretion rates of DOPA, DA, the DA me tabolite dihydroxyphenylacetic acid (DOPAC), the sympathetic neurotran smitter norepinephrine (NE), the NE metabolite dihydroxyphenylglycol ( DHPG), and the adrenomedullary hormone epinephrine (EPI) were measured in 70 American normotensive volunteers of different ages, sex, and ra ce, and 35 Israeli Caucasian males in their sixth decade, with no diet ary or activity restrictions. In both groups, the excretion rate of DO PAC (overall mean 12.53 +/- 1.08 (SEM) mu moles/day) exceeded by far t hose of all other catechols combined. Catechol excretion rates were po sitively inter-correlated in both subject groups-especially DA with DO PA (r=0.71 across all subjects, p<0.001). Excretion rates of catechols were also positively correlated with the excretion rate of sodium in both groups (for DOPA r=0.70 across all subjects, p<0.001; for DA r-0. 54, p<0.001; for DOPAC r=0.46, p<0.001; for NE r=0.47, p<0.001; and fo r EPI r=0.29, p<0.01), but not with urine volume. DA and DOPA excretio n rates were higher in Black Americans than in Caucasian Americans (2. 50 +/- (SEM) 0.19 vs 1.86 +/- 0.10 mu moles/d, p<0.01; 0.21 +/- 0.02 v s 0.16 +/- 0.01 mu moles/d, p<0.01); DA excretion decreased with incre asing subject age (r=-0.24); and excretion rates of DOPA were negative ly correlated with MAP (r=0.33, p<0.01). The high rate of urinary excr etion of DOPAC probably mainly reflects glomerular filtration or tubul ar secretion of plasma DOPAC. The multiple positive correlations among excretion rates of catechols indicate a common source, such as couple d synthesis and turnover of catecholamines in the sympathoadrenal syst em. Positive correlations of excretion rates of DOPA, DA, and DOPAC wi th ad libitum dietary salt intake are consistent with salt-induced act ivation of a renal DOPA-DA natriuretic system.