[The positive inotropic activity of 5-bromoisatin (5-bromo-indoline-2,3-dione)].

The inotropic activity of 5-bromisatin (5-bromindolyn-2,3-dion) which possesses antihypoxic properties was studied on rhythmically stimulated papillary muscles of guinea pigs, and the changes in the force of their contractions were recorded. The inotropic efficacy (calculated according to ED50 value) of 5-bromisatin was approximately 5 times less than that of milprinon. The activity of the isatin drug was inhibited by about 30% by carbachol and prazosin and relieved by nifedipin. 5-bromisatin increases sharply (by 160%) the second component (P2) of the biphase contraction and its effect is independent of the receptor beta-adrenergic blocking agent dl-propanolol. On the basis of the obtained data it is concluded that Ca2+ ions entering by way of the slow (L-type) calcium channels both the cAMP-dependent and cAMP-independent routes are involved in the mechanism of 5-bromisatin activity.