Selective Norepinephrine Reuptake Inhibition as a Human Model of Orthostatic Intolerance

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Abstract
Background — Observations in patients with functional mutations of the norepinephrine transporter (NET) gene suggest that impaired norepinephrine uptake may contribute to idiopathic orthostatic intolerance. Methods and Results — We studied the effect of the selective NET blocker reboxetine and placebo in a randomized, double-blind, crossover fashion on cardiovascular responses to cold pressor testing, handgrip testing, and a graded head-up tilt test (HUT) in 18 healthy subjects. In a subset, we determined isoproterenol and phenylephrine sensitivities. Subjects ingested 8 mg reboxetine or placebo 12 hours and 1 hour before testing. In the supine position, heart rate was 65±2 bpm with placebo and 71±3 bpm with reboxetine. At 75° HUT, heart rate was 84±3 and 119±4 bpm with placebo and with reboxetine ( P P Conclusions — Selective NET blockade creates a phenotype that resembles idiopathic orthostatic intolerance. This observation supports the hypothesis that disordered norepinephrine uptake mechanisms can contribute to human cardiovascular disease. Our study also suggests that NET inhibition might be useful in preventing vasovagal reactions.