Evaluation of muscarinic M-3-receptor antagonism of Solenostemma argel leaves

Solenostemma argel (Del.) Hayne is a perennial shrub widely distributed in the deserts of North Africa. The decoction of the leaves was used in folk medicine as a antispasmodic for the treatment of various colic [1]. Continuing our researches on S. argel [2], in the present study we investigated the implication of colinergic system, in particular of muscarinic receptors, in the spasmolytic action of S. argel leaves decoction and two kempferol glycodides (1, 2) isolated from methanol extract. Detailed phytochemical investigations were carried out on the decoction by HPLC-MSn. The evaluation of spasmolytic activity of the extract and two compounds has been performed on the guinea-pig ileum smooth muscles contracted by cholinergic agonist carbachol. In the same experimental conditions, papaverine has been tested for comparison. The decoction reduces the contraction to carbachol in a concentration-dependent manner. Moreover, the decoction reduced the maximum response to carbachol, defining a non-competitive antagonism. The flavonoid 1 has not elicited any antagonistic M3 activity, while 2 has shown a non-competitive and concentration-dependent antagonism toward M3 muscarinic receptors. The effects of 2 is similar to those induced by papaverine, but at a concentration about two order of magnitude lower. Concluding these preliminary results suggest that the spasmolytic and antispasmodic effects of S. argel phytocomplex might be mediated by M3-receptor antagonism and justify its use in folk medicine in several intestinal diseases.