Abstract
The reserve power of myocardial muscle depressed by Ethrane was determined by means of changes in time interval of stimulation in seven isolated cat papillary muscles. Ethrane (average concentration of 6.5 ± 0.1 mg/100 ml) decreaesd maximal isometric forces to 56 per cent of the control value at the “rested-state contraction” (RSC). Ethrane also decreased maximal isometric force (Fm) and rate of force development (dF/dt) at any given time interval of stimulation. Slopes of both time interval-force and time intcrval-dF/dt curves were unaffected by Ethrane. The percentage depressions in Fm and dF/dt were reduced from 44 and 37 to 25 and 21 per cent by decreasing the time interval from 240 sec to 3.2 sec. The ability of heart muscle to respond to changes in time interval of stimulation was, therefore, maintained during administration of Ethrane. Possible mechanisms of myocardial depression induced by Ethrane are discussed.
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