[Inhibitory effect of 6 beta-acetoxy nortropane on respiration]

6 beta-AN (6 beta-acetoxy nortropane), a novel selective M2-receptor agonist, caused decrease in FR, TV, MVV and pO2 and increase of pCO2 when intravenous injection of 10 micrograms.kg-1 in conscious rabbits or 2, 5, 20 micrograms.kg-1 in conscious dogs was given (P < 0.05 or 0.01). The inhibitory effect on MVV exhibited a dose-dependent relationship. Small doses of 6 beta-AN icv (0.5, 1, 2, 4 micrograms.kg-1 in the conscious rabbits) and iva (0.25, 0.5 and 1.0 micrograms.kg-1 in anesthetized dogs) decreased FR, TV, MVV and pO2 and increased pCO2 as well. These results were reversed after administration of AF-DX116 and enhanced after administration of pirenzepine. Thus, it appears that the inhibitory action of 6 beta-AN on respiration might be related to stimulation of the inhibitory M2 cholinergic receptor in respiratory center.