Abstract
Helenalin, a pseudoguaianolide sesquiterpene lactone which has hitherto been known as a potent antitumor and cytotoxic substance was found in this study to have a positive inotropic effect (PIE) on the myocardium. Left atrial strips and papillary muscles isolated from the guinea-pig heart were driven at a frequency of 1.0 Hz in Krebs-Henseleit solution at 30°C. Helenalin produced an increase in the force of contraction (Fc) depending on its concentration in the range between 10-5-10-3M. The potency of helenalin, expressed as pD2 value, was 4.69 and 4.11 in the left atria and papillary muscle, respectively. The PIE of 3×10-4M helenalin was equivalent to 78% of that of 10-5M norepinephrine. The PIE of a higher concentration of helenalin (above 3×10-4M) was neither affected by reserpinization nor by propranolol (3×10-5M), but the PIE at lower concentrations was inhibited by reserpinization or propranolol. We conclude that the PIE of helenalin is produced in two different ways ; one is catecholamine-mediated and the other is an unknown direct effect.
