Central sympatholysis as a novel countermeasure for cocaine-induced sympathetic activation and vasoconstriction in humans.
OBJECTIVE
The aim of this study was to determine whether cocaine's sympathomimetic actions can be reversed by a potent centrally acting alpha2 adrenergic receptor (AR) agonist (dexmedetomidine).


BACKGROUND
We recently showed that cocaine stimulates the human cardiovascular system primarily by acting in the brain to increase sympathetic nerve activity (SNA), the neural stimulus to norepinephrine release. Thus, SNA constitutes a putative new drug target to block cocaine's adverse cardiovascular effects at their origin.


METHODS
In 22 healthy cocaine-naïve humans, we measured skin SNA (microneurography) and skin blood flow (laser Doppler velocimetry) as well as heart rate and blood pressure before and after intranasal cocaine (2 mg/kg) alone and in combination with dexmedetomidine or saline.


RESULTS
During intranasal cocaine alone, SNA increased by 2-fold and skin vascular resistance increased from 13.2 +/- 2.3 to 20.1 +/- 2.2 resistance units while mean arterial pressure increased by 14 +/- 3 mm Hg and heart rate by 18 +/- 3 beats/min (p < 0.01). Dexmedetomidine abolished these increases, whereas intravenous saline was without effect. Dexmedetomidine was effective in blocking these sympathomimetic actions of cocaine even in all 7 subjects who were homozygous for the Del322-325 polymorphism in the alpha2C AR, a loss-of-function mutation that is highly enriched in blacks.


CONCLUSIONS
The data advance the novel hypothesis that central sympatholysis with dexmedetomidine constitutes a highly effective countermeasure for cocaine's sympathomimetic actions on the human cardiovascular system, even in individuals carrying the alpha2CDel322-325 polymorphism. (Study to Improve Scientific Understanding of the Cardiovascular Actions of Cocaine; http://clinicaltrials.gov/ct/show/NCT00338546?order=1; NCT00338546).
Menon
Dileep V
DV
Hypertension Division and the Donald W. Reynolds Cardiovascular Clinical Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8586, USA.
Wang
Zhongyun
Z
Fadel
Paul J
PJ
Arbique
Debbie
D
Leonard
David
D
Li
Jia-Ling
JL
Victor
Ronald G
RG
Vongpatanasin
Wanpen
W
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000328:Adult; D003042:Cocaine / Q000494:pharmacology*; D020927:Dexmedetomidine / Q000494:pharmacology*; D005260:Female; D006720:Homozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics; D012867:Skin / Q000098:blood supply / Q000187:drug effects* / Q000294:innervation; D014655:Vascular Resistance / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014666:Vasomotor System / Q000187:drug effects*
C547774:ADRA2C protein, human; D000316:Adrenergic alpha-Agonists; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D020927:Dexmedetomidine; D003042:Cocaine