Local anaesthetic activity of monoterpenes and phenylpropanes of essential oils

The local anaesthetic activity of a number of compounds with different structures, contained in essential oils, was studied. Anaesthetic activity was evaluated in vivo in the rabbit conjunctival reflex test and in vitro in a rat phrenic nerve-hemidiaphragm technique. Among the substances tested terpineol and trans-anethole (10(-3)-1 mug/ml) were able to drastically reduce the electrically evoked contractions of rat phrenic nerve-hemidiaphragm in a concentration-dependent manner, but not eugenol, (-)- and (+)-citronellal, (-)- and (+)-carvone, trans cinnamaldehyde and alpha -terpinene. In the rabbit conjunctival reflex test, the treatment with a solution of terpineol and trans-anethole (10-100 mug/ml) effected a concentration-dependent increase in the number of stimuli required to evoke the reflex, thus confirming in vivo the local anaesthetic activity observed in vitro. Eugenol, (-)- and (+)-citronelial, trans-cinnamaldehyde, (-)- and (+)-carvone and a-terpinene were as ineffective in the in vivo test as they were in the in vitro results.