Evaluation of increased norepinephrine excretion in hypertension using L-dopa-3H.

Four hypertensive patients with features of sympathoadrenal hyperactivity similar to those of patients with pheochromocytoma had rates of excretion of norepinephrine plus epinephrine (̂ u,g/day) of 135 ± 13 (mean ± SE) compared with 441 ± 59 in five patients with pheochromocytoma and 53 ± 7 in six patients with primary hypertension. The specific activities of urinary norepinephrine and the half-life of the rate of their decline were determined for each patient for 24 hours after intraneuronal labeling of norepinephrine using L-dopa-H. The initial specific activities of norepinephrine (dpm/m/j,mole) and the half-life of the rate of their decline (hours) for the three groups were 2,920 ± 670 and 3.8; 291 ±89 and 4.2; and 6.782 ± 1,003 and 6.0, respectively. However, the observed differences in the half-life values were not significant. The findings indicated that the rate of release and excretion of newly synthesized norepinephrine was increased in patients with hypertension and sympathoadrenal hyperactivity. Less than 1% of the infused L-dopa-H was converted to norepinephrine in the chromaffin tumors of patients with pheochromocytoma, resulting in low specific activities of urinary norepinephrine; this may be of diagnostic value in hypertensive patients who have equivocally increased rates of norepinephrine excretion. The autonomic hyperactivity, hypertension, and excessive norepinephrine excretion in the four patients without pheochromocytoma may have been related to unidentified forms of stress.