Free and conjugated catecholamines in plasma and red blood cells of normotensive and hypertensive patients.

Plasma free and conjugated norepinephrine levels were found to be significantly increased in patients with labile and sustained hypertension whereas epinephrine levels were normal in these patients. While free NE and E levels increased significantly during postural change, conjugated NE and E levels were not altered by this stimulus suggesting that conjugated NE levels could be an index of chronic rather than acute changes in the sympathetic tone. In hypertensive patients, plasma free dopamine levels increased during postural change and conjugated DA levels tended to be higher suggesting a dysfunction in the dopamine metabolism. Red blood cells were also found to contain free and conjugated CA. While conjugated CA levels in red blood cells (RBC) were equal or lower than in the plasma, free CA were found in larger concentrations than in the plasma. In hypertensive patients conjugated CA levels in RBC were similar to those found in normotensive subjects but free NE and E levels were significantly higher in hypertensive patients. These studies demonstrate various abnormalities in the metabolism of CA in hypertensive patients. Each of these could contribute to the maintenance of hypertension by an alteration of the biological expression of the sympathetic tone at the cellular level of these patients.