The effect of calcium on the inotropy of catecholamine and paired electrical stimulation in the newborn and adult myocardium.

Abstract

This study was designed to determine the age-related difference in the inotropic effect of isoproterenol and paired electrical stimulation in newborn and adult rabbits, and to explore the influence of calcium on the inotropic effect of these interventions. Baseline myocardial contractility in the newborn was significantly less than that in the adult. The sensitivity to the inotropic effect of isoproterenol was similar in the two age groups. Both time to peak tension and half-relaxation time were equally shortened by isoproterenol in both age groups. The maximal inotropic effect of calcium in the newborn was significantly greater than that in the adult. The net inotropic effect of isoproterenol and paired electrical stimulation expressed as % of control [+dTdt(max)] in the newborn was significantly greater than that in the adult. However, the absolute increase in +dT/dt(max)/g tissue during these interventions was similar in both age groups. Higher calcium concentration was required in the newborn to abolish the net inotropic effect of both isoproterenol and paired electrical stimulation. These data suggest that: (1) the biochemical responsiveness to isoproterenol was similar in the two age groups and (2) the lower intracellular calcium concentration in the newborn might be responsible for the greater inotropic effect of calcium, isoproterenol, and paired electrical stimulation in this age group.