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Evidence for a peripheral component in the sympatholytic actions of clonidine and guanfacine in man

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The time courses of the changes in plasma growth hormone and noradrenaline concentrations in response to 15 min infusions of clonidine 0.2 mgs and guanfacine 2 mgs, were studied in six normal volunteers, in a double-blind, randomised, crossover study. Plasma noradrenaline fell within 15 min of the commencement of drug administration, by 36±14% after clonidine (p<0.05) and by 32±11% (p<0.05) after guanfacine. Plasma growth hormone was not significantly elevated until the 30th minute to 12.0±4.7 lU/ml (p<0.05) after clonidine and 14.7±11.5 lU/ml (p<0.05) after guanfacine, having been undetectable prior to both drugs. The reduction in plasma noradrenaline by these α2-adrenergic agonists, prior to activation of central adrenoceptors as detected by changes in plasma growth hormone, is evidence for a peripheral component in their sympatholytic effect.

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Murphy, M.B., Brown, M.J. & Dollery, C.T. Evidence for a peripheral component in the sympatholytic actions of clonidine and guanfacine in man. Eur J Clin Pharmacol 27, 23–27 (1984).

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Key words

  • hypertension
  • alpha2-adrenoceptors
  • blood pressure
  • clonidine
  • guanfacine
  • healthy volunteers