An increase in urinary catecholamines of renal origin in patients with "borderline" hypertension

Plasma and urinary catecholamines (norepinephrine and epinephrine) and urinary dopamine excretion were studied in 45 essential hypertensive patients subdivided into borderline (labile) and stable hypertension. Borderline hypertensive patients had a higher mean fractional renal clearance of catecholamines (the clearance of catecholamines relative to creatinine clearance) than both control subjects and stable hypertensive patients. A significantly positive correlation between the renal clearance of catecholamines and urinary dopamine excretion was also found in those with borderline hypertension, but not in control subjects or those with stable hypertension. These data indicate that patients with borderline hypertension have a relatively exaggerated renal catecholamine release. They probably reflect an increased sympathetic discharge to the kidney in "borderline" hypertension, occuring to a lesser degree in stable hypertension and control subjects. Thus, urinary catecholamine measurements do not specifically reflect the level of circulating catecholamines, particularly in borderline hypertension.