Diagnostic use of metoclopramide in hypertension caused by pheochromocytoma

We studied 5-mg metoclopramide provocation in six pheochromocytomatous patients with different tumor locations, varying secretory patterns and large tumor sizes (> 12 g or equivalently) and in 14 patients with essential hypertension as part of diagnostic work-up, usually after screening with vanillylmandelic acid assay by the colorimetric method. Antihypertensive medication continued in three and five patients, respectively. Despite similar basal blood pressures patients with pheochromocytomas developed more prominent pressor responses in five of six patients than the nonpheochromocytomatous patients (P < 0.01), most (10) of the latter with negligible pressor responses. Basal plasma catecholamines were higher in each of the pheochromocytomatous patients of different secretory patterns. Further rises after provocation were seen in all pheochromocytomatous patients except one with early pressor response, and also in one nonpheochromocytomatous patient. All tests were well tolerated. Thus, we concluded that the metoclopramide test based upon joint pressor response and plasma catecholamine response can be safely used in the diagnosis of pheochromocytoma. A less stringent protocol including a short drug-off preparatory period may be a warranted compromise between feasibility and diagnostic accuracy.