The Effect of Thyme Extract on β₂-Receptors and Mucociliary Clearance

Abstract

Thyme is a broncholytic und secretomotoric agent. Thus, our aim was to investigate the influence of a thyme extract on β₂-receptors in competition binding experiments and relaxation experiments on rat uteri and trachea. Furthermore, the influence of the extract on respiratory clearance was of interest. Binding experiments were performed using purified rat lung membranes with the β₂-receptor ligand [¹²⁵I]-CYP {[¹²⁵I]-(±)-Iodocyanopindolol}. The transport of the fluorescence dye rhodamin 123 concerning ciliary action in the tracheal area of a mouse was investigated using a microdialysis technique. The thyme extract reduces only slightly [¹²⁵I]-CYP binding and amplifies the displacement of [¹²⁵I]-CYP by propranolol (non-specific β-receptor antagonist): the displacement curve in the concentration range representing β₂-receptors (nM) is shifted to the left. Thyme extract had relaxing effects on organs possessing β₂-receptors (uterus and trachea). The propranolol-induced antagonism to isoprenaline is reverted concentration-dependently by the extract. A duplication of the rate of ciliary clearance by the extract was observed. In conclusion: 1) There is evidence for an influence of a thyme extract on β₂-receptors by both binding studies and biological effects: As can be derived from the shift of the propranolol displacement curve (nM), ingredients of the thyme extract slightly interact with β₂-receptors in rat lung tissue. This effect is indirect since no full range competition curve was reached. 2) An at least indirect interaction with β₂-receptors in rat uteri and trachea is revealed by a decreased antagonism of propranolol on the relaxing effect of isoprenaline by the plant extract. 3) An additional mechanism is presumed because at high extract concentrations isoprenaline-induced relaxation is complete, whereas the displacement of propranolol at β₂-receptors is only weak. 4) Thyme extract has an indirect (modulatory) effect on the β₂-receptor system. 5) Mucociliary clearance is improved in vivo. Its mechanism has still to be elucidated.

Key words

Thymus vulgaris - Lamiaceae - thyme extract - β₂-receptors - mucociliary clearance - trachea

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