Relaxant effects on tracheal and ileal smooth muscles of the guinea pig

The effects of volatile oils of 22 plants from 11 different families and of some of their constituents on tracheal and ileal smooth muscles were investigated. The results were compared with the relaxant effects of catecholamines and phosphodiesterase inhibitors. All of the oils had relaxant effects on the tracheal smooth muscle, the most potent were angelica root, clove, elecampane root, basil and balm leaves oil. 16 oils inhibited the phasic contractions of the ileal myenteric plexus-longitudinal muscle preparation, the most potent were elecampane root, clove, thyme, balm leaves and angelica root oil. 2 oils (anise and fennel) increased the phasic contractions, and 4 oils (bitter orange, caraway, mace, pepper) produced a marked increase in resting force (i.e. contracture). In regard to the relaxant effects, most of the 16 oils were more potent on the ileal than on the tracheal muscle. However, a small group of 4 oils (angelica root, clove, basil, black caraway) had a higher relaxant effect on the tracheal than on the ileal muscle. This was also found to be the case with eugenol, eugenol acetate and cinnamic aldehyde as well as with isoprenaline and phosphodiesterase inhibitors.