Impact of Thymol in Thyme Extracts on Their Antispasmodic Action and Ciliary Clearance

Abstract

Thyme is a herb with broncholytic und secretomotoric effects. Its activity on β₂ receptors as a possible mechanism of action was demonstrated. Major components are thymol and carvacrol which are claimed to be responsible for its effects and, therefore, used for standardization in the German pharmacopoeia (0.03 % phenols calculated as thymol). Our aim was to investigate the impact of thymol by using thyme extracts with either normal or extremely low thymol concentrations (< 0.005 % or > 0.038 %). The antispasmodic effect on smooth muscles of the trachea and the ileum and the effect on ciliary activity (respiratory clearance) were investigated. In addition, pure thymol and carvacrol were investigated separately and in spiking experiments. Thymol and carvacrol had a concentration-dependent antispasmodic effect in the rat trachea either being stimulated by acetylcholine, K⁺ or Ba⁺⁺. The same result was observed with respect to the increase of mucociliary transport in mice. Extracts with very low thymol contents are effective in all models used except acetylcholine-induced rat ileum contraction. When thyme extracts with normal thymol contents or with very low thymol contents were compared, the extract with normal thymol contents was more effective, both as a relaxant (rat ileum) and as an antispasmodic compound (rat trachea contraction induced by either acetylcholine, Ba⁺⁺ or K⁺) and in ciliary transport experiments. Thyme extracts with very low thymol contents (practically free of volatile oil) were equally effective with respect to endothelin effects. When an extract with very low thymol contents is spiked with increasing concentrations of thymol, a concentration-dependent increase concerning the antispasmodic effect (Ba⁺⁺-induced trachea contraction) is observed. In conclusion, the data show that in various models of antispasmodic effect (ileum and trachea) and by measuring ciliary activity, thymol (and carvacrol) is (are) active, although other not identified components of thyme extract appear to be very important as well, since extracts with very low thymol contents are active. On the basis of these results the standardization on thymol alone appears not to be justified.

Key words

Thymus vulgaris L. - Lamiaceae - thyme extract - thymol - antispasmodic effect - mucociliary clearance - trachea

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