Spasmolytic Effect of Grewia asiatica Fruit Extract on Isolated Smooth Muscles is Mediated via Multiple Pathways

Grewia asiatica Linn, or phalsa, is a commonly consumed fruit in Pakistan. The fruit is employed in the traditional medicine practice of Pakistan as a smooth muscle relaxant in different gastrointestinal (GI) and cardiovascular diseases. In this investigation, we show the antispasmodic and vasorelaxant actions of Grewia asiatica fruit extract.

A 70% methanolic crude extract of the plant material was prepared (Ga.Cr). Different isolated GI tissue preparations and endothelium-intact aortas from rats were utilized to observe the pharmacological actions of the extract.

Ga.Cr, in increasing concentrations, inhibited the spontaneously contracting rabbit jejunum. In an effort to determine the mechanism of this relaxant action, contractions were induced in jejunum and ileum tissues with K⁺ (80 mM). Ga.Cr was able to only partially inhibit these induced contractions indicating that the mechanism might not be completely through a blockade of Ca²⁺ channels (CCB). When tested on low K⁺-(25 mM) sustained contractions, Ga.Cr cumulatively suppressed these contractions (0.1-10 mg/ml), indicating an opening of K⁺ channels (KCO) as the mechanism. Cromakalim, a standard KCO, was also more specific in blocking low K⁺-induced contractions. For the effect in aorta tissues, Ga.Cr suppressed the agonist-induced contractions from 0.3 mg/ml to 10 mg/ml. Upon challenge with L-NAME, a nitric oxide (NO) blocker, the extract response curve shifted right, indicating vasodilation was mediated via endothelial NO.

This study shows that GI antispasmodic and vasodilator activities of Ga.Cr may be mediated via a KCO mechanism in the GI tract and through the release of NO from vascular endothelium.