Natural resistance to effects of morphine in Octodon degus: A South American rodent

Octodon degus a South American caviomorph, presents a natural resistance to some effects of morphine. On respiratory rate none of the doses of morphine (i.v.) employed produced a significant modification of this parameter. The administration of morphine, leu-enkephalin and β-endorphin to isolated O. degus vas deferens did not change significantly the electrically induced muscular twitch. Brain concentration of ¹⁴C morphine in the rat, as compared to O. degus, showed statistically significant differences. Pentazocine modified the EEG of O. degus, while morphine had no effect. Pimozide produced only a partial change of the pentazocine effect on EEG. This result is consistent with the view that pentazocine interacts with different opiate receptors.