Chronotropic and inotropic effects of neurotensin on spontaneously beating auricles

Synthetic neurotensin (NT) was shown to exert a potent positive inotropic and chronotropic action in spontaneoulsy beating guinea pig and rat auricles and to be inactive in the rabbit auricles. The positive inotropic effects of NT in guinea pig and rat auricles were detected at concentrations as low as 3.0--6.0 x 10-10 M. Maximal concentrations of NT (3.1 X 10-7 M) increased the amplitude of contractions by 135 and 55% in guinea pig and rat auricles, respectively. On the basis of ED50 values, NT was found to be 20--30 times more potent than epinephrine in increasing the force of contraction in guinea pig and rat auricles. The results suggested that the positive inotropic and chronotropic actions of NT are species dependent. The potential usefulness of NT in the treatment of experimentally induced heart failure is underlined.