Force and Oxygen Consumption in the Immature Rabbit Heart

Abstract

ABSTRACT. We speculated that there are important agerelated differences in the economy of left ventricular force development in the isolated heart. To assess this, we evaluated oxygen consumption and force development in newborn (less than 1 wk old) (n = 26), juvenile (4-6 wk old) (n = 26), and adult (5-7 mo old) (n = 26) isolated, isovolumic rabbit hearts. Measurements were obtained with three different interventions, including 1 ) changes in heart rate, 2) inotropic stimulation with isoproterenol, and 3) changes in end-diastolic pressure. We found no significant baseline differences in the economy of force development. However, when heart rate was increased by 20%, the force/oxygen consumption ratio (economy) increased in newborn hearts by approximately 37%, whereas there was a decrease in juvenile and adult hearts of -27%. In addition, with increases in end-diastolic pressure above 10 mm Hg, newborn hearts increased their force/myocardial oxygen consumption ratio to 300% of the baseline value, whereas adults increased to only 160% of baseline. Isoproterenol produced no significant age-related differences in the force/myocardial oxygen consumption ratio. We conclude that there are important age-related differences in the economy of left ventricular force development in this model, but these differences are apparent only at higher heart rates and end-diastolic pressures. (Pediatr Res 27: 476-482,1990) of myosin isozyme V, was greatest in the newborn and lowest in the adult (3). Furthermore, Kissling and Rupp (5) have demonstrated in rats that the degree of catecholamine-induced increase in myocardial oxygen consumption depends on the isoenzyme pattern of myosin. Perhaps the force/oxygen consumption ratio also changes with alterations in myocardial isoenzymes, although there are no data to confirm this.We know that the newborn heart has a less mature sarcoplasmic reticulum than the adult. Mahony (6) demonstrated that there was a marked increase in the coupling of sarcoplasmic reticulum Ca2+ transport to ATP hydrolysis during maturation of the heart. In sheep, this maturational process seems to continue through the 8th wk of life. We speculated that this maturation of calcium coupling ratio might manifest as a developmental increase in the economy of myocardial force development.Thus, there are fundamental biochemical differences between the newborn and adult myocardium. Differences in myosin isozyme or sarcoplasmic reticulum could conceivably alter the coupling of ATP hydrolysis to force generation. Therefore, we hypothesized that there might be important maturational changes in the economy of myocardial force generation independent of changes in ventricular pressure or volume. To further assess this, we evaluated oxygen consumption and force development in newborn, juvenile, and adult isolated, isovolumic rabbit hearts. Abbreviations MATERIALS AND METHODSdP/dt, change in pressure per unit time Methods. Standard techniques for an isolated, isovolumic rabbit heart preparation were modified primarily to isolat...

Oxidative and Glycogenolytic Capacities within the Developing Chick Heart

“…Such a relationship between energy expenditure and cardiac frequency is also illustrated in Figure 2b. As in our preparation, increasing HR does not alter myocardial suprabasal O 2 consumption in isolated immature rabbit heart perfused in the presence of glucose (49). Thus, during the embryonic/fetal life, the capability of the working myocardium to use preferentially energy derived from glycolysis could also protect the cardiovascular function against occasional hypoxic stress.…”

“…In the loaded heart at stage 24HH, the ratio of basal to total ventricular O 2 consumption was rather large (68%) compared with the ratio of 30 to 50% found in neonatal (49) and adult hearts (50 -52). This could be partly explained by the important energy consumed by biosynthetic activity in the rapidly growing heart.…”

Values of T/QRS ratio in pregnancies complicated by intrauterine growth restriction

“…In addition, as shown by the studies on the fetal heart physiology, the fetal heart muscle consumes much less oxygen than the adult heart muscle to cause contraction of the same strength [27] . Fetal myocardial cells are immature and have better tolerance to hypoxia [28] .…”