A preliminary study of the effect of essential oils on skeletal and smooth muscle in vitro.

The pharmacological activity of nine commercial essential oils was studied on the rat isolated phrenic nerve diaphragm preparation and compared with activity on field-stimulated guinea-pig ileum preparations. The essential oils at final bath concentrations of 2 x 10(-5) and 2 x 10(-4) g/ml produced four different effects on skeletal muscle, whilst only a contracture with or without a decrease in response to field stimulation in smooth muscle. The first type of effect on skeletal muscle involved a contracture and inhibition of the twitch response to nerve stimulation shown by a sample of clary sage, dill, fennel, frankincense and nutmeg; a second, shown by thyme produced a contracture without a change in the twitch response; a third, shown by lavender reduced the twitch response alone and the fourth, shown by camphor, increased the size of the twitch response. Angelica root oil at the highest concentration studied showed no response on skeletal muscle.