title: The effect of clonidine on plasma MHPG: evidence against tonic alpha 2-adrenoceptor control of noradrenergic function.
abstract: The effect of the alpha 2-adrenoceptor agonist clonidine on plasma free MHPG levels was assessed in 12 normal volunteers. A significant fall in MHPG was produced by 1.5 microgram X kg-1 clonidine IV whereas saline had no effect. The peak fall in MHPG correlated strongly with the area under the curve (AUC). In addition, a strong correlation was seen between basal MHPG and the extent of the clonidine-induced fall. This suggests that plasma MHPG levels are not simply a reflection of central alpha 2-adrenoceptor function and argues against tonic alpha 2-adrenoceptor-mediated inhibitory control of noradrenergic output.
mesh_terms: D000328:Adult; D003000:Clonidine / Q000494:pharmacology*; D006018:Glycols / Q000097:blood*; D006801:Humans; D007700:Kinetics; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000097:blood*; D009638:Norepinephrine / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology
chemical_list: D006018:Glycols; D011942:Receptors, Adrenergic, alpha; D008734:Methoxyhydroxyphenylglycol; D003000:Clonidine; D009638:Norepinephrine