Tritium excretion after intravenous administration of tritium labelled adrenaline and noradrenaline and digital vascular reactivity to adrenaline and noradrenaline in normotensive and labile hypertensive subjects.

1. The 24-h urinary excretion of tritium after tritiated adrenaline administration and digital vascular reactivity to exogenously administered adrenaline and noradrenaline were measured in ten normotensive and in twenty-eight labile essential hypertensive subjects. Tritiated noradrenaline excretion and apparent noradrenaline secretion rate were also measured in ten and eleven of these subjects, respectively. 2. Despite overlapping, the mean 24-h tritium excretion after 3H-adrenaline administration as well as reactivity to adrenaline were significantly greater in the hypertensive than in the normotensive subjects, whether or not they had increased responsiveness to noradrenaline. Significant correlation, however, was observed between tritium excretion of adrenaline and reactivity to adrenaline in both labile hypertensive and normotensive subjects. These measurements were also both significantly correlated with percentage variability in systolic and diastolic blood pressure in the labile hypertensive subjects. 3. No significant correlation was observed between adrenaline as against noradrenaline measurements, whether physiological or biochemical, in either hypertensive or normotensive subjects.