Opioid‐like antinociceptive effects of oral administration of a lectin purified from the seeds of Canavalia brasiliensis

The objective of this study was to evaluate the antinociceptive effects of a lectin from Canavalia brasiliensis (ConBr) when administered orally to murine models of chemical and thermal nociception. ConBr up to 100 mg/kg produced significant and dose‐dependent antinociceptive effects: 81% reduction in abdominal writhing induced by 0.6% acetic acid; 26 and 52% reduction in early‐ and late‐stage paw licking, respectively, induced by 2.5% formalin; and 155% increase in reaction latency (heightened thermal pain threshold). In all models, the antinociceptive effect was reversed by the lectin‐binding carbohydrate α‐d‐methyl‐mannoside and by the nonselective opioid antagonist naloxone. The antinociceptive effect observed in the formalin test was inhibited by the δ‐selective antagonist naltrindole and the κ‐selective antagonist nor‐binaltorphimine but not by the μ‐selective antagonist cyprodime. In conclusion, when administered orally to Swiss mice, the ConBr lectin displayed antinociceptive activity, both peripheral and central, mediated by the opioid system and involving δ‐and κ‐receptors and the lectin domain.