THE ACTIONS OF DIGITALIS LEAF PREPARATIONS AND OF CARDIAC GLYCOSIDES ON THE ISOLATED RIGHT VENTRICLE OF THE GUINEA PIG

Abstract A method is described for recording kymographically the systolic contraction and the resting length of the electrically stimulated, isolated right ventricle of the guinea pig. Two samples of Digitalis purpurea leaf and a sample of Digitalis lanata have been assayed in terms of the Third International Standard of D. purpurea using metameters dependent on changes in the systolic contractions and resting length of the muscle and the time elapsing before the changes occur. In a similar manner digitoxin and ouabain have been assayed in terms of digoxin. The results are compared with those obtained by slow intravenous infusion of the preparations into guinea pigs. The potencies derived from the two methods are in close agreement in the case of the digitalis leaf preparations. Digitoxin, however, is more active than digoxin on the ventricle preparation irrespective of the metameter used and less active by the slow infusion method, while ouabain has the same activity as digoxin on the ventricle and twice the activity by the infusion method. The results for ouabain on the ventricle using the different metameters, are homogenous, those for digitoxin are not. There is little difference between the general actions of the three glycosides on the ventricle but each glycoside is capable of producing different effects on systolic contraction and resting length depending on the dose employed. The possible mechanisms responsible for these effects are discussed.