title: Evidence for a peripheral component in the sympatholytic actions of clonidine and guanfacine in man.
abstract: 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, cross-over study. Plasma noradrenaline fell within 15 min of the commencement of drug administration, by 36 +/- 14% after clonidine (p less than 0.05) and by 32 +/- 11% (p less than 0.05) after guanfacine. Plasma growth hormone was not significantly elevated until the 30th minute to 12.0 +/- 4.7 lU/ml (p less than 0.05) after clonidine and 14.7 +/- 11.5 lU/ml (p less than 0.05) after guanfacine, having been undetectable prior to both drugs. The reduction in plasma noradrenaline by these alpha 2-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.
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D013006:Growth Hormone / Q000097:blood; D016316:Guanfacine; D006146:Guanidines / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006993:Hypnotics and Sedatives; D007263:Infusions, Parenteral; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010648:Phenylacetates / Q000494:pharmacology*; D013565:Sympatholytics
chemical_list: D006146:Guanidines; D006993:Hypnotics and Sedatives; D010648:Phenylacetates; D013565:Sympatholytics; D016316:Guanfacine; D013006:Growth Hormone; D003000:Clonidine; D009638:Norepinephrine