Clonidine suppression test

Pheochromocytoma diagnosis (overnight clonidine suppression test) 0.3 mg... 

A problem with the clonidine suppression test is that patients with normal or mildly increased plasma levels of norepinephrine may have clonidine-induced decreases in plasma norepinephrine, despite the presence of a pheochro-... 

Bravo EL, Tarazi RC, Fouad PM, Vidt DG, Gifford RW, Jr. Clonidine-suppression test a useful aid in the diagnosis of pheochromocytoma. N Engl J Med 1981 305 623-6. 

Taylor HC, Mayes D, Anton AH. Clonidine suppression test for pheochromocytoma examples of misleading results. J Clin Endocrinol Metab 1986 63 238-42. 

Clonidine (Catapres) is an imidazoline which is an agonist to ctj-adrenoceptors (postsynaptic) in the brain, stimulation of which suppresses S5unpathetic outflow and reduces blood pressure. At high doses it also activates peripheral a -adrenoceptors (pre-synaptic autoreceptors) on the adrenergic nerve ending these mediate negative feedback suppression of noradrenaline release. In overdose clonidine can stimulate peripheral Oj-adrenoceptors (postsynaptic) and thus cause hypertension by vasoconstriction. Clonidine was discovered to be hypotensive, not by the pharmacologists who tested it in the laboratory but by a physician who used it on himself as nose drops for a common cold. The tl is 6 h. 

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