Autonomic control after blockade of the norepinephrine transporter: a model of orthostatic intolerance.
Orthostatic intolerance is a debilitating syndrome characterized by tachycardia on assumption of upright posture. The norepinephrine (NE) transporter (NET) has been implicated in a genetic form of the disorder. We assessed the combined central and peripheral effects of pharmacological NET blockade on cardiovascular regulation and baroreflex sensitivity in rats. NE reuptake was blocked chronically in female Sprague-Dawley rats by the NET antagonist desipramine (DMI). Treated animals demonstrated an elevated supine heart rate, reduced tyramine responsiveness, and a reduced plasma ratio of the intraneuronal NE metabolite dihydroxyphenylglycol relative to NE, all of which are consistent with observations in human NET deficiency. Spectral analysis revealed a dramatic decrease in low-frequency spectral power after DMI that was consistent with decreased sympathetic outflow. Stimulation of the baroreflex with the vasodilator nitroprusside revealed an attenuated tachycardia in DMI-treated animals. This indicated that the DMI-induced sympathoinhibitory effects of increased NE in the brain stem predominates over the functional elevation of NE stimulation of peripheral targets. Thus attenuated baroreflex function and reduced sympathetic outflow may contribute to the orthostatic intolerance of severe NET deficiency.
Carson
Robert P
RP
Autonomic Dysfunction Center, Vanderbilt University, Nashville, Tennessee 37232-2195, USA.
Diedrich
André
A
Robertson
David
D
D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000818:Animals; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001835:Body Weight; D003891:Desipramine / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives* / Q000097:blood; D009638:Norepinephrine / Q000097:blood; D050484:Norepinephrine Plasma Membrane Transport Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D012791:Shy-Drager Syndrome / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000187:drug effects*; D027981:Symporters / Q000037:antagonists & inhibitors*; D013610:Tachycardia / Q000503:physiopathology*
D018759:Adrenergic Uptake Inhibitors; D050484:Norepinephrine Plasma Membrane Transport Proteins; C493226:Slc6a2 protein, rat; D027981:Symporters; D008734:Methoxyhydroxyphenylglycol; D003891:Desipramine; C010117:3,4-dihydroxyphenylglycol; D009638:Norepinephrine