phenylephrine , the least potent , had only about one-sixtieth of the activity of clonidine.2 the antinociceptive action appears to occur within the peritoneum , since it was apparent almost immediately after the drugs were injected and was produced by doses far smaller than were effective by the subcutaneous route.3 alpha-adrenoceptors appear to be involved in the reaction , since noradrenaline showed stereospecificity , and the alpha-adrenoceptor antagonists phentolamine and piperoxan both shifted the dose-response curves of the alpha-adrenoceptor agonist drugs to the right , usually parallel to the control curves.4 the high antinociceptive potency of clonidine and oxymetazoline , indicate the importance of alpha ( 2 ) -adrenoceptors and this was supported by the finding that piperoxan was a more effective antagonist than phentolamine .
C0034784
alpha-adrenoceptors
C0001639
alpha ( 2