Cardioactivity of 2mg/ml Leonotis leonurus in the Langendorf rat heart not due to [K+] and [Mg2+]

Dried crude aqueous extracts of the leaves of the medicinal plant Leonotis leonurus (Ll) in Krebs–Henseleit perfusion buffer (K-H) showed cardiovascular effects at a concentration of 2mg/ml (2mgLL) in isolated constant pressure (74mmHg) Langendorf perfused Wistar rat hearts. Results are shown throughout as mean±SD, n=6 and significance was taken as P<0,05. 2mgLL did not have significantly increased [Na⁺], [Cl^-], [Ca²⁺]& [PO₄ ^2-]. In 2mgLL [K⁺] increased significantly (from 6.0±0.1 to 10.625±0.3mg/ml) and [Mg²⁺] (from 0.415±0.095 to 1.707±0.037mg/ml). Effects of K-H with [K⁺] equal to 2mgLL (HighK), and K-H with both [K⁺] and [Mg²⁺] equal to that of 2mgLL (HighMgK) was compared to that of 2mgLL. Test solutions were applied for 5min. Cardiac work (CW)=heart rate (HR) x developed pressure (P _dev). Interventricular septal temperature was kept at 37°C. A water-filled PVC balloon in the left ventricle and a transducer coupled to an A/D converter in a PC monitored left ventricular pressure. 2mgLL significantly increased diastolic pressure (301±85%) and coronary perfusion (58.9±11.4%) but decreased HR (-96.1±29.9%), P_dev (-96.9±3.7%) and CW (-95±11.2%) significantly. HighK had no significant effect on any of the parameters while the HighMgK had effects opposite in direction to that of the 2mgLL. Neither the HighK, nor the HighMgK therefore mimicked the changes caused by 2mgLL. The effects of the 2mgLL is therefore not due to the altered ionic composition of the perfusion fluid caused by adding 2mg/ml Leonotis leonurus extract to the K-H.