Differential analgesic activity of the enantiomers of atropine derivatives does not correlate with their muscarinic subtype selectivity

Article abstract of DOI:10.1016/S0223-5234(97)83285-0

The enantiomers of several tropic and p-substituted tropic acid esters related to atropine obtained by esterification under non-racemizing conditions after resolution of the corresponding racemic acids [(+)- and (-)-18, (+)- and (-)-19] are reported. They were tested in vitro on muscarinic subtype receptors and in vivo for their analgesic activity on mice. As in the case of the lead compound, R-(+)-hyoscyamine, these substances show enantioselectivity in analgesic tests, the eutomers being the R-(+) or R-(+)-p-substituted tropic acid derivatives. However, this property, which is a consequence of increased central release of ACh, seems unrelated to muscarinic subtype selectivity insofar as the compounds are unable to discriminate muscarinic subtype receptors. A possible explanation of these results which does not involve subtype selectivity is proposed, based on the recently developed concept of inverse agonism.