Bioassay-directed isolation of falcarindiol and isoacetovanillon from Pycnocycla caespitosa based on KCl-induced contraction in rat uterus smooth muscles

Hydroalcoholic extract and essential oil of aerial parts of Pycnocycla caespitosa have spasmolytic activity on rat ileum contractions. The objective of this research was to separate fractions of total hydroalcoholic extract of P. caespitosa guided by their spasmolytic activity on rat uterus. Aerial parts of P. caespitosa were extracted with ethanol. The concentrated extract was subjected to column chromatography and thin layer chromatography (TLC) for isolation fractions, then one of the bioactive fractions was subjected to further isolation to find its active components. Five fractions were obtained (Fr.1-Fr.5) and their anti-spasmodic activities were examined on uterus contraction induced by KCl (80 mM) and compared with ritodrine. In addition, spasmolytic effect of Fr.4 (one of the bioactive fractions) was determined on rat uterus induced by oxytocin (0.0005 IU/mL) and compared with ritodrine. Hydroalcoholic extract of P. caespitosa (0.032-2 mg/mL) reduced the responses to KCl but the inhibitory effect was not complete with 2 mg/mL extract in the bath. Four fractions (Fr.1, Fr.2, Fr.3 and Fr.4) (32-500 μg/mL) inhibited rat uterus contractions on the uterus while Fr.4 was slightly more active than others (IC₅₀ = 146 ± 23 μg/mL). Falcarindiol and isoacetovanillone were identified from Fr.4 using phytochemical methods including high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and TLC. In conclusion, in this research bioactivity guided technique was successfully used for separation of active fraction of P. caespitosa. Falcarindiol and isoacetovanillone were identified from the active fraction which inhibited both tonic and rhythmic contractile responses in rat isolated uterus.