Effects of yohimbine on naloxone-induced antinociception in a rat model of inflammatory hyperalgesia.
Effects of the alpha2-adrenoceptor antagonist yohimbine on the antinociception produced by a low dose of naloxone were examined in a rat model of carrageenan-induced inflammation. In rats receiving saline prior to naloxone injection, the low dose of naloxone (5 microg/kg, i.p.) significantly prolonged paw withdrawal latency in response to noxious thermal stimuli for both the inflamed and the non-inflamed paws 4 h after carrageenan injection (6.0 mg in 0.15 ml saline). In rats receiving yohimbine, the low dose of naloxone failed to produce prolongation of paw withdrawal latencies 4 h after carrageenan, whereas naloxone produced antinociception 7 days after carrageenan. The results suggest that noradrenergic mechanisms are involved in naloxone-induced antinociception only in the early phase of carrageenan-induced inflammation.
Tsuruoka
M
M
Department of Physiology, Showa University School of Dentistry, Tokyo, Japan.
Hiruma
Y
Y
Matsutani
K
K
Matsui
Y
Y
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000627:therapeutic use*; D000818:Animals; D002351:Carrageenan; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy*; D007249:Inflammation / Q000139:chemically induced / Q000188:drug therapy*; D007274:Injections, Intraperitoneal; D008297:Male; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015016:Yohimbine / Q000008:administration & dosage / Q000627:therapeutic use*
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D009292:Narcotic Antagonists; D015016:Yohimbine; D009270:Naloxone; D002351:Carrageenan