Coupling SFE to uterotonic bioassay: an on-line approach to analysing medicinal plants

Supercritical fluid extraction has been directly coupled on-line to a uterotonic bioassay, using guinea pig uterine smooth muscle in vitro. This technique was developed for the detection of uterotonic compounds present in medicinal plants used during pregnancy to induce or augment labour. The direct passage of CO2 into the muscle chamber led to adiabatic cooling of the physiological fluid and inhibition of muscle contraction. This was alleviated by the construction of a CO2 reduction interface together with the passage of carbogen which aided in the rapid displacement of excess CO2. The on-line system was evaluated with four plants (Clivia miniata (Lindl.) Regel, Ekebergia capensis Sparrm., Grewia occidentalis L. and Asclepias fruticosa L.) that are currently used during pregnancy by some black South African women. Extractions were performed with water modified supercritical CO2. Fractions of supercritical fluid extracts, obtained by sequentially increasing the pressure from 200 to 300 and 400 atm at constant temperature were transferred directly to the muscle chamber to identify the active fractions. The 400 atm extracts of C. miniata, A. fruticosa and E. capensis displayed maximum uterotonic activity while only the 300 atm extract of G. occidentalis induced uterine muscle contraction. This technique proved to be a safe and sensitive method for analyzing medicinal plants that contain uterotonic substances hence assisting in rapidly validating the uterotonic properties and detecting any toxic effects of these extracts.