Some observations on the effects of enantiomers of two benzomorphan narcotic antagonists and atropine on analgesia, tremor and hypothermia produced by oxotremorine.

The action of the benzomorphan narcotic antagonists Mr-1452 and Mr-2266 and their respective (+) isomers Mr-1453 and Mr-2267 as well as the antimuscarinic agent atropine upon oxotremorine (OTMN)-induced analgesia, tremor, and hypothermia were investigated in mice. The (+) isomers Mr-1453 (1.0 mg kg-1 i.p.) and Mr-2267 (2.0 mg kg-1 i.p.), but not the (-) isomers (Mr-1452 and Mr-2266) in doses up to 2.0 mg kg-1 i.p. after 30 min pretreatment produced a significant and parallel shift in OTMN's analgesic dose-response line, assessed by the hot plate test (55 degrees C). None of the isomers tested produced any significant change in OTMN induced tremor or hypothermia. This contrasted with atropine (0.5 mg kg-1 i.p.) which antagonized all three pharmacological parameters. The present data indicate that OTMN-induced analgesia in mice may involve a neuronal substrate which, at least partly, differs from those subserving tremor and hypothermia. In addition it supports the notion that cholinergic analgesia exhibits stereospecific sensitivity to the (+) isomers of narcotic antagonists.