Studies on the mechanism of positive inotropic effect of hymoquinolone

Mechanism of positive inotropic action of hymoquinolone (7-hydroxy-8-methoxy-4(1H)-quinolone) (Q), a new compound isolated from Chinese Soft Sinularia polydactyla and Sinularia lettoclados, was studied using radioimmunoassay. Q caused positive inotropic action accompanied by elevated cAMP level in left and right atria of guinea pig at the concentration of 0.34 mM. The evidence that Q inhibited phosphodiesterase activity and did not affect adenylate cyclase activity led to the conclusion that Q may be an inhibitor of phosphodiesterase, thereby increasing cAMP level and producing positive inotropic actions.