A comparison of the antinociceptive and adverse effects of the mu-opioid agonist morphine and the delta-opioid agonist SNC80.

Abstract

delta-Opioid receptor agonists have been postulated to induce analgesia without the adverse effects commonly associated with mu-opioids e.g. morphine. In the present study, we evaluated the occurrence of antinociceptive and opioid-like side effects in rats (n=5-7) treated with a single dose of subcutaneous morphine (0.01 to 40 mg/kg) or SNC80 (0.63 to 80 mg/kg). The antinociceptive effects of morphine and SNC80 were compared using a range of nociceptive tests including the tail withdrawal test, the acetic acid-induced abdominal constriction (writhing) assay, the automated formalin test and a model of inflammation-induced thermal hyperalgesia. The adverse effects of both drugs were examined in animal models for gastrointestinal (GI) inhibition (charcoal test; ricinus oil test), respiratory depression (blood-gas analysis), motor disturbances (automated rotarod model) and abuse liability (drug discrimination learning). Morphine displayed significant antinociceptive and adverse effects in all the animal models employed. SNC80 exhibited a significant effect in the writhing test and limited efficacy in a model of inflammation-induced thermal hypersensitivity. A delay in the occurrence of diarrhoea and some limited increases in PCO(2) were observed with the higher doses of SNC80 (> or =40 mg/kg). In conclusion, the delta-opioid agonist SNC80 lacks both the analgesic efficacy and adverse effects of mu-opioids. However, the activity of SNC80 in the inflammatory model suggests delta-opioid agonists may be useful analgesics in the treatment of some forms of inflammatory pain.

• Authors: Elizabeth L Gallantine, Theo F Meert
• Journal: Basic & clinical pharmacology & toxicology (Basic Clin Pharmacol Toxicol) Vol. 97 Issue 1 Pg. 39-51 (Jul 2005) ISSN: 1742-7835 [Print] England
• PMID: 15943758 (Publication Type: Comparative Study, Journal Article)

Chemical References

• Benzamides
• Piperazines
• Receptors, Opioid, delta
• Receptors, Opioid, mu
• Carbon Dioxide
• 4-(alpha-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide
• Morphine

Topics

• Animals
• Benzamides (pharmacology, toxicity)
• Carbon Dioxide (blood)
• Discrimination Learning (drug effects)
• Hyperalgesia (drug therapy)
• Male
• Morphine (pharmacology, toxicity)
• Motor Activity (drug effects)
• Pain (drug therapy)
• Piperazines (pharmacology, toxicity)
• Rats
• Rats, Sprague-Dawley
• Receptors, Opioid, delta (agonists)
• Receptors, Opioid, mu (agonists)