Norepinephrine Depletion in Idiopathic Orthostatic Hypotension

Five patients with idiopathic orthostatic hypotension and defective vasoconstrictor responses to the Valsalva maneuver and to application of ice to the forehead were found to have absent vasoconstriction in the forearm in response to intra-arterial administration of tyramine and enhanced vasoconstrictor responses in response to intra-arterial administration of norepinephrine. These findings strongly suggested norepinephrine depletion from the nerve endings and inability of the sympathetic nerve endings to take up norepinephrine. The depletion of norepinephrine from sympathetic nerve endings was confirmed in four patients by demonstrating histochemically the absence of catecholamine-specific fluorescence in sympathetic vasomotor nerves from deltoid muscle. It is suggested that depletion of norepinephrine from nerve endings was responsible for autonomic dysfunction and orthostatic hypotension in these patients.