Adenosine A1 but not A2a receptor agonist reduces hyperalgesia caused by a surgical incision in rats: a pertussis toxin-sensitive G protein-dependent process.
BACKGROUND
Activation of A1 adenosine receptors (A1Rs) causes antinociception after nerve injury and inflammation. However, the role of A2a adenosine receptors (A2aRs) for pain processing is less clear. In the current study, the authors investigated the role of spinal adenosine A1Rs and A2aRs for the maintenance of mechanical hyperalgesia in an animal model for postoperative pain.


METHODS
Rats with intrathecal catheters were anesthetized and underwent plantar incision. Spontaneous pain behavior and withdrawal threshold to punctuate stimulation were measured before and after administration of intrathecal R-phenylisopropyl-adenosine (R-PIA; A1R agonist), 2-w p-2-carbonyl-ethyl-phenylethylaminox-5X-N-ethylcarboxami-doadenosine (CGS21680; A2aR agonist), or vehicle. In separate groups of animals, the effects of pertussis toxin, forskolin, glibenclamide, 4-aminopyridine, tetraethylammonium, apamin, charybdotoxin, or margatoxin on R-PIA-induced antinociception were examined.


RESULTS
Intrathecal administration of 5 nmol R-PIA but not 10 nmol CGS21680 decreased nonevoked spontaneous pain behavior. Furthermore, intrathecal administration of R-PIA but not of CGS21680 increased withdrawal thresholds after incision. Pretreatment with pertussis toxin and administration of forskolin, glibenclamide, 4-aminopyridine, and tetraethylammonium inhibited R-PIA-induced antinociception. In addition, intrathecal administration of apamin, charybdotoxin, or margatoxin did not modify mechanical hypoalgesia mediated by R-PIA.


CONCLUSIONS
Spinal A1Rs but not A2aRs play an important role in the maintenance of nonevoked and evoked pain behaviors after an incision. Furthermore, A1R-induced spinal antinociception is mediated by interactions with pertussis toxin-sensitive G proteins. In addition, the opening of adenosine triphosphate-sensitive K channels but not of calcium-activated potassium channels and voltage-gated Kv1.3 or Kv1.6 channels contribute to the antinociceptive effect of A1R agonists.
Zahn
Peter K
PK
Department for Anaesthesiology and Operative Intensive Care, University of Muenster, Muenster, Germany. schmerz@uni-muenster.de
Straub
Heidrun
H
Wenk
Manuel
M
Pogatzki-Zahn
Esther M
EM
D000241:Adenosine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D058907:Adenosine A1 Receptor Agonists; D058908:Adenosine A2 Receptor Agonists; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000187:drug effects* / Q000378:metabolism; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology; D008297:Male; D010149:Postoperative Pain / Q000188:drug therapy; D037342:Pertussis Toxin / Q000494:pharmacology*; D010660:Phenylisopropyladenosine / Q000008:administration & dosage / Q000494:pharmacology; D010812:Physical Stimulation; D026902:Potassium Channel Blockers / Q000008:administration & dosage / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013514:Surgical Procedures, Operative / Q000009:adverse effects*; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology
D058907:Adenosine A1 Receptor Agonists; D058908:Adenosine A2 Receptor Agonists; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014665:Vasodilator Agents; D010660:Phenylisopropyladenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000241:Adenosine