Antinociceptive effects of the 6-O-sulfate ester of morphine in normal and diabetic rats: Comparative role of mu- and delta-opioid receptors

In vivo analysis of morphine- and M6S-induced (i.p.) antinociception was examined by hot water tail flick latency test in naive and diabetic rats. In vitro experiments to determine opioid receptor affinity and activation of post-receptor events utilized Chinese hamster ovary (CHO) cells transfected with human mu- or delta-ORs. M6S produced more potent antinociception than morphine in both naïve and diabetic rats. The data imply that the improved analgesic and tolerance profile of M6S over morphine may be due to the ability of M6S to act at both mu- and delta-ORs.