Herbal Amara extract induces gastric fundus relaxation via inhibition of the M2 muscarinic receptor.

Abstract

Background: Impaired gastric accommodation is one of the most frequent symptoms of functional dyspepsia. The safety and efficacy of conventional treatments remain to be proven and alternative herbal therapies have been proposed to alleviate gastrointestinal symptoms. This preclinical study examined the role of herbal Amara extract (containing Artemisia absinthium, Centaurium erythraea, Cichorium intybus, Gentiana lutea, Juniperus communis, Achillea millefolium, Peucedanum ostruthium, Salvia officinalis, and Taraxacum extracts) on gastric (fundus) accommodation and the possible implication of muscarinic receptors in its regulation.

Methods: The effect of Amara extract on fundus motility was investigated in organ baths of smooth muscle strips isolated from the fundus of guinea pigs, and the role of the muscarinic receptor pathway was evaluated using functional and radioligand binding assays in cell lines expressing the M2 or M3 muscarinic receptor.

Key results: Amara extract inhibited carbachol-induced contraction of guinea pig smooth muscle strips in a dose-dependent manner. This relaxant effect was not affected by the M3 antagonist J-104129. Amara extract also inhibited M2, but not M3, receptor activity in CHO-K1 cells (IC₅₀ 219 μg mL^-1), and specifically bound the M2 receptor (IC₅₀ 294 μg mL^-1). Of the nine herbal components of Amara extract, Juniperus communis, P. ostruthium, and Salvia officinalis inhibited M2 receptor activity (IC₅₀ 32.0, 20.8, and 20.1 μg mL^-1, respectively), and P. ostruthium was sufficient to reverse carbachol-induced ex vivo contraction of guinea pig fundic smooth muscles.

Conclusion and inferences: Amara extract relaxes gastric smooth muscles by inhibiting the M2 muscarinic receptor. This study suggests the potential benefit of Amara extract for patients with impaired gastric accommodation.