Some pharmacological, toxicological and phytochemical investigations on Centaurea phyllocephala

Abstract

Centaurea phyllocephala Boiss. has been used in folkloric medicine as an antidiabetic agent. Present investigations on various extracts of C. phyllocephala revealed that basal plasma glucose concentration and plasma glucose response to glucose load were either elevated or unchanged by the i.v. administration of these extracts in anaesthetized rats or by i.p. or oral administration of the extracts in conscious rats. The predominant effect of C. phyllocephala is the toxicity in rats and mice and this indicates the presence of some toxic or active compounds which merit phytochemical isolation. Further, C. phyllocephala extracts also caused either an initial brief hypotension followed by a delayed hypertension or produced no changes when injected i.v. in the rats. The hypotensive effect was inhibited by atropine whereas the hypertensive effect was prevented by phentolamine or guanethidine but not by hexamethonium. The alcoholic extract also induced an initial brief negative inotropic effect, followed by delayed prolonged positive inotropic and negative chronotropic effects on the spontaneous inotropic and negative chronotropic effects on the spontaneous contractions of the guinea pig right atrium. The initial depressing effect and the delayed positive inotropic effect were inhibited by pretreatment with atropine. The extract of C. phyllocephala also produced a contractile activity on guinea pig ileum strips and this could be prevented by atropine. No significant diuretic effect was produced by the extract. Phytochemical screening revealed that C. phyllocephala contains tertiary and quaternary alkaloids, sesquiterpenic lactones, methylated flavones and their glycosides, as well as leuco- and proanthocyanidines. Further studies on sesquiterpenic lactones and methylated flavones resulted in the isolation of lactones with α-methylene γ-lactone and methylene side chain on the cyclopentyl ring as well as of four methylated flavones (hispidulin, nepetin, cirsiliol, jaceosidin) structurally closely related to the cytotoxic flavonoids of other Compositae plants.