Alpha1-adrenergic receptors augment P2X3 receptor-mediated nociceptive responses in the uninjured state.
In the present study, the adrenergic receptor (AR) subtype mediating adrenergic augmentation of P2X(3) receptor-mediated nociceptive responses on sensory nerve endings was examined by using selective AR receptor agonists and antagonists in Sprague Dawley rats in the uninjured state. Local administration of alphabeta-methyleneATP (ligand for P2X3/P2X2/3 receptors) into the plantar hind paw produced few pain behaviors when given alone in this strain of rats; combination with adrenaline (alpha1- and alpha2-AR agonist) and phenylephrine (alpha1-AR agonist) but not clonidine or UK 14,304 (alpha2-AR agonists) increased flinching behaviors. Flinching produced by noradrenaline (NA)/alphabeta-methyleneATP was suppressed by low doses of prazosin (alpha1-AR antagonist), and this reduction was selective compared with yohimbine (alpha2-AR antagonist). Prazosin also reduced flinching produced by phenylephrine/alphabeta-methyleneATP. Using thermal threshold determinations, adrenaline and phenylephrine but not clonidine or UK 14,304, mimicked the action of NA in augmenting reductions in thermal thresholds produced by alphabeta-methyleneATP. Terazosin (another alpha1-AR antagonist) inhibited hyperalgesia produced by NA/alphabeta-methyleneATP. These results provide evidence for alpha1-AR involvement in adrenergic augmentation of P2X3/P2X2/3 receptor-mediated responses on sensory nerve endings in the uninjured state in Sprague Dawley rats.


CONCLUSIONS
This study indicates the alpha1-adrenergic receptor subtype mediates adrenergic augmentation of the activation of sensory nerves by purinergic P2X3 receptors (respond to ATP) in the periphery. Observations are potentially relevant to chronic pain conditions in which sympathetic nerves influence sensory nerves.
Meisner
Jason G
JG
Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.
Waldron
James B
JB
Sawynok
Jana
J
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D004347:Drug Interactions / Q000502:physiology; D004357:Drug Synergism; D005528:Foot / Q000503:physiopathology; D006930:Hyperalgesia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D010146:Pain / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism*; D058477:Receptors, Purinergic P2X3; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism*; D017779:Sympathetic Fibers, Postganglionic / Q000187:drug effects / Q000378:metabolism
D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018340:Receptors, Adrenergic, alpha-1; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; D000255:Adenosine Triphosphate