Response to ouabain in acutely and chronically failed canine heart-lung preparations

The actions of ouabain were studied in canine heart-lung preparations (HLP) under four different sets of procedures and the therapeutic, irregularity and lethal doses of ouabain determined. Two different methods than those usually used for producing failure in HLP are presented. Acute heart failure was produced by either elevating Starling resistance or administering an excessive amount of the beta-adrenoceptive blocking agent, propranolol. Surgically induced heart-failure was produced by reducing the size of dogs aortae to 20–25% of its original diameter. Ouabain elicited a marked inotropic response in HLP in all three of these procedures, although the response was more rapid in onset in preparations failed acutely than in those which were normal or chronically failed. An increase of dp/dt was found to be a more sensitive criterion of ouabain's beneficial effect, than were criteria formerly used, i.e. an increase in cardiac output or a decrease in right atrial pressure. Our results are in agreement with the view that it is difficult to elicit a beneficial effect to ouabain in normal HLP, but that ouabain's effects may be easily demonstrated in failed preparations. This study demonstrated that the myocardium from chronically failed animals is more sensitive to ouabain in vitro than is the myocardium of normal animals.