Abstract
We examined whether the chronic administration of selective κ-opioid agonists could produce antitussive tolerance, in a comparison with the μ-opioid morphine. A certain degree of tolerance to the antitussive effects of morphine appeared in rats treated chronically with this drug. However, chronic administration of U-50, 488H and U-62, 066E, highly selective agonists for the κ-opioid receptor, does not result in the development of tolerance to their respective antitussive effects. These results suggest that the ability of κ-opioid agonists to cause tolerance to their respective antitussive effects was lower than that of a μ-opioid agonist.
