FREQUENCY-FORCE RELATIONSHIP IN THE RABBIT AURICLE AND ITS MODIFICATION BY SOME METABOLIC INHIBITORS’

The effect of previous activity or quiescence on myocardial contractility was first described by Bowditch (1871). Working with the frog heart, he noted that following a period of rest, stimulation resulted in a staircase-like series of beats of increasing force of contraction. He called this phenomenon “treppe”, and its existence has been confirmed by many authors (reviewed by Szent-Gyorgyi, 1953). Most authors have observed that any increase in contraction frequency results in increased contractility. On the other hand, a few authors have observed in mammalian myocardium the opposite effect, i.e., a temporary potentiation of contractility following rest (rest potentiation) (Rosin and Farah, 1955; Brooks et al., 1955; Katzung and Farah, 1956). A similar and probably related reversal of the classical Bowditch treppe has been observed at very low rates in rat ven-tricle by McDowall et al. (1955) and in turtle myocardium by Katzung and Farah (1956). Another reversal of the Bowditch treppe occurs at high frequencies of contraction, where a further increase in frequency results in decreased con-tractility. One purpose of the present study was to further define the inotropi