Epinephrine, phenylephrine, and methoxamine induce infiltrative anesthesia via alpha1-adrenoceptors in rats.
OBJECTIVE
To assess whether epinephrine, phenylephrine, and methoxamine act via certain subtypes of adrenoceptors to exert their local anesthetic activity.


METHODS
We investigated cutaneous anesthesia from adrenoceptor agonists and/or antagonists in conscious, unanesthetized Sprague-Dawley male rats (weight 200-250 g). Cutaneous anesthesia was evidenced by a block of the cutaneous trunci muscle reflex, which is characterized by reflex movement of the skin over the back produced by twitches of lateral thoracispinal muscles in response to local dorsal cutaneous noxious pinprick.


RESULTS
Local infiltration of epinephrine, L-phenylephrine, or methoxamine alone induces cutaneous anesthesia in rats in a dose-dependent way. Epinephrine is found to be 19 and 29 times more potent than those of methoxamine and L-phenylephrine, respectively. The cutaneous anesthesia induced by epinephrine, phenylephrine, or methoxamine can be significantly reduced by alpha(1)-adrenoceptor antagonists (eg, prazosin), alpha1, alpha2-adrenoceptor antagonist, alpha(1A)-adrenoceptor antagonist (eg, 5-methylurapdil), alpha(1B)-adrenoceptor antagonist (eg, chloroethylclonidine), or alpha(1D)-adrenoceptor antagonist (eg, BMY7873).


CONCLUSIONS
Our results indicate that epinephrine, phenylephrine and methoxamine all act mainly via mixed subtypes of alpha(1)-adrenoceptors to induce cutaneous anesthesia in the rat.
Shieh
Ja-ping
JP
Department of Anesthesiology, Chi Mei Medical Center, Tainan, Taiwan, China.
Chu
Chin-chen
CC
Wang
Jhi-joung
JJ
Lin
Mao-tsun
MT
D058668:Adrenergic alpha-1 Receptor Antagonists; D000772:Anesthesia, Local; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D005996:Nitroglycerin / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects*
D058668:Adrenergic alpha-1 Receptor Antagonists; D000779:Anesthetics, Local; D010879:Piperazines; D018340:Receptors, Adrenergic, alpha-1; C057446:5-methylurapidil; D010656:Phenylephrine; C051731:chlorethylclonidine; D005996:Nitroglycerin; D008729:Methoxamine; D009543:Nifedipine; C053428:BMY 7378; D003000:Clonidine; D011224:Prazosin; D004837:Epinephrine; D010646:Phentolamine