title: Force and oxygen consumption in the immature rabbit heart.
abstract: We speculated that there are important age-related 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 approximately 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.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75335.
authors.forename: M D
authors.initials: MD
authors.lastname: Parrish
authors.forename: S
authors.initials: S
authors.lastname: Farrar
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D011817:Rabbits; D016276:Ventricular Function
chemical_list: D007545:Isoproterenol