Effect of cardiac glycosides on the coronaries: physiologic and morphologic studies in the dog heart.

The effect of K- strophanthoside on coronary blood flow (CBF) was studied in open chest dogs anaesthetized with pentobarbital sodium. K- strophanthoside (3.5 and 7.0 X 10(-8) mol X kg-1 i.v.) elicited a dose-dependent decrease of CBF and an increase of late diastolic coronary resistance. Intracoronary injections of the drug (1.2 X 10(-8) mol) produced selective coronary constriction. The haemodynamic pattern indicated a direct vasoconstrictor effect, independent of the extracoronary (cardiotonic) action of the drug. In the polarization microscope Romh anyi 's aldehyde bisulphite-toluidine blue (ABT) reaction as adapted for the detection of cardiac glycosides showed profuse binding of strophanthoside to the coronary vessel wall. K- strophanthoside significantly reduced the CBF increase elicited by adenosine infusion (2 X 10(-7) mol X kg-1) into the left heart. Verapamil (4 X 10(-7) mol X kg-1, i.v.), on the other hand, counteracted the strophanthoside action on CBF. The results suggest that restricted intracellular availability of Ca2+, a prerequisite of physiologic CBF increase, is opposed by cardiac glycosides.