Free and conjugated plasma catecholamines in hypertensive patients with and without pheochromocytoma.

SUMMARY A total of 17 hypertensive patients suspected of having a pheochromocytoma underwent venous catheterization to determine their free and conjugated plasma catecholamines (CA). Six of the patients were found to have a pheochromocytoma; the seventh, an adrenomedullary hyperplasia. The venous outflow from the site adjacent to toe tumor, when compared to the respective site of sampling in essential hypertensive patients, was characterized by a very high outflow of free (and sometimes an absence of conjugated) CA that resulted in an abnormally high ratio of free-to-conjugated CA; the CA conjugates themselves were rarely elevated. Venous sampling at the peripheral site showed that at the height of the paroxysms, the peripheral venous system in these patients was flooded by free norepinephrine (NE) or epinephrine (E); and by free dopamlne (DA) in another patient who had low blood pressure. The three patients with the most peripheral "flooding" by free CA at the height of the paroxysm had, even In toe normotensive phase, lower conjugated plasma NE + E (p < 0.01), DA (p < 0.05), and higher urinary vanillylmandelic add (VMA) excretion (p < 0.02) than the other three patients; one of the latter had only conjugated catecholamines, extremely elevated, during paroxysms. The subgroups with low and high conjugates could not be clearly separated clinically, but two of the three patients with high conjugates had less frequent crises. The patient with the adrenomedullary hyperplasia had unremarkable changes in free CA; only the finding of elevated conjugated CA suggested the possibility of adrenomedullary hyperfunction. Conjugation appears to be one of the major inactivation pathways of CA released from a pheochromocytoma. Patients with low levels of conjugates are more susceptible to a sudden overflow of free CA without a concomitant rise of conjugated CA and to have a higher VMA excretion than patients with high concentrations of conjugated CA. The type of CA, however, is eventually decisive for the clinical presentation, notwithstanding the extent of conjugation. The presence of high levels of conjugated CA may suggest adrenomedullary hyperfunction even in the absence of other diagnostic criteria.