The local anaesthetic activity of a number of compounds with different stru
ctures, 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 terp
ineol 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 r
abbit conjunctival reflex test, the treatment with a solution of terpineol
and trans-anethole (10-100 mug/ml) effected a concentration-dependent incre
ase 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-terpinen
e were as ineffective in the in vivo test as they were in the in vitro resu
lts.