Effect of crude extracts from Leonotis nepetaefolia (Labiatae) on rat and guinea-pig smooth muscle and rat cardiac muscle.

The actions of hydroalcoholic and tea extracts of stems of Leonotis nepetaefolia on agonist-induced and electrically-evoked contractions have been analysed in-vitro in rat uterus and left atrium and in guinea-pig ileum and trachea. The tea extract (500-2000 micrograms mL-1) caused parallel and graded rightward shifts of concentration-response curves to bradykinin and BaCl2 in the rat isolated uterus, but antagonized responses to prostaglandin F2 alpha in a typically non-competitive manner. The hydroalcoholic extract also caused rightward displacements of the curves to bradykinin, acetylcholine (ACh), angiotensin II, oxytocin and BaCl2 and reduced their maximal contractile effects. Both extracts (30-3000 micrograms mL-1) relaxed uterine preparations precontracted with KCl (80 mM), the hydroalcoholic extract being about 2-fold more potent than the tea extract. The relaxant response to the former was unaffected by propranolol (1 microM) or forskolin (10 nM), but was potentiated 2-fold by 3-isobutyl-1-methylxanthine (10 microM). In the guinea-pig ileum the hydroalcoholic extract shifted the ACh- and bradykinin-induced contractile curves to the right and markedly inhibited their maximal effects, whereas the tea extract caused a typical non-competitive antagonism of ACh-induced contractile responses. In field-stimulated ileal strips, both extracts (3-3000 micrograms mL-1) caused contractions and inhibited twitch responses. Guinea-pig tracheal rings precontracted with carbachol (0.3 microM) were relaxed only by concentrations of either extract in excess of 1000 micrograms mL-1, an action that was unaffected by propranolol (0.1 microM) or by offomethacin (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)