Effects of some cardiotonic agents on contractility of skinned fibers from mammalian heart.

Nine cardiotonics of different chemical structure were investigated on their ability to influence calcium-induced isometric contractions of chemically skinned porcine myocardial fibers. It was found that at a concentration of 10(-4) mol/l amrinone, enoximone, imazodan, milrinone, piperanometozine and piroximone were without effect on calcium-induced tension development of skinned fibers. 3-Amino-6-methyl-5-phenyl-2(1H)-pyridinone (APP), pimobendan and sulmazole enhanced the isometric contractions induced by 0.66 mumol/l Ca++ concentration-dependently. The intrinsic activity of pimobendan was much higher than for sulmazole or APP. Comparing equieffective concentrations inducing 35% additional tension development, the rank order of potency was: pimobendan greater than APP greater than sulmazole.