Receptor-mediated biological effects of extracts obtained from three species.

This study reports the effects of aqueous extracts obtained from three fern species of Bulgarian origin: L., L., and L. on the contractility and bioelectrogenesis of rat gastric smooth muscle tissues. In the concentration range 0.015-0.150 mg/mL the three extracts contracted smooth muscle tissues in a concentration-dependent manner. The contractions caused by L. and L. extracts (0.150 mg/mL) were reduced by ketanserin (5 × 10 and 5 × 10 mol/L), an antagonist of serotonin 5-HT2 receptor. The contraction evoked by L. (0.150 mg/mL) was significantly reduced by 1 × 10 mol/L atropine, an antagonist of muscarinic receptors, and turned into relaxation against the background of 3 × 10 mol/L galantamine. After combined pretreatment with galantamine and l-arginine (5 × 10 mol/L), this relaxation become more pronounced. The study demonstrates that constituents of L. and L. extracts act as agonists of 5-HT2 receptors and cause contraction by activating serotonergic signaling system. L.-induced reaction is an additive result of two opposite-in-character effects. The dominant contraction is initiated by inhibition of acetylcholinesterase activity. The relaxation develops with pre-inhibited acetylcholinesterase, it is significantly potentiated by l-arginine, and therefore associated with nitrergic signaling pathway.