Decreased contractile efficiency and increased nonmechanical energy cost in hyperthyroid rabbit heart. Relation between O2 consumption and systolic pressure-volume area or force-time integral.
- 1 April 1990
- journal article
- research article
- Published by Ovid Technologies (Wolters Kluwer Health) in Circulation Research
- Vol. 66 (4), 999-1011
- https://doi.org/10.1161/01.res.66.4.999
Abstract
Both systolic pressure-volume area (PVA) and force-time integral (FTI) have been used as measures of oxygen consumption per beat (VO2) in the isolated left ventricle. The reciprocal of the slope of the VO2-PVA relation has been considered to reflect the chemomechanical energy transduction efficiency of the contractile machinery (contractile efficiency), whereas its VO2 intercept consists of energy cost of excitation-contraction coupling and basal metabolism. To examine whether the increase in myosin isoform V1/V3 ratio in hyperthyroid rabbits decreases contractile efficiency and to determine overall mechanisms of higher oxygen consumption in hyperthyroid hearts, the VO2-PVA and VO2-FTI relations as well as the end-systolic pressure-volume relation were assessed in cross-circulated, isovolumically beating hearts isolated from normal, hyperthyroid, and hypothyroid rabbits. Normalized initial slopes of the rising limb of the curvilinearly fitted end-systolic pressure-volume relation (E'max, ventricular contractility index) were similar for normal and hyperthyroid groups. However, the slopes and VO2 intercepts of the VO2-PVA and VO2-FTI relations were greater in hyperthyroid hearts than in normal hearts. Accordingly, in the hyperthyroid hearts, the contractile efficiency (27 +/- 6%) was lower and left ventricular VO2 for excitation-contraction coupling (0.028 +/- 0.004 ml O2/beat/100 g) was higher than in normal hearts (40 +/- 4% and 0.021 +/- 0.005 ml O2/beat/100 g, respectively). This decreased contractile efficiency in the hyperthyroid hearts was attributable to myosin isoform alteration rather than to increased beta-adrenoceptors because isoproterenol did not affect the slope of the VO2-PVA relation in all groups. In contrast, the slope of the VO2-FTI relation was significantly increased by isoproterenol in all groups. Neither the VO2-PVA nor the VO2-FTI relations in hypothyroid hearts were different from those in normal hearts except for significantly lower VO2 for basal metabolism. We conclude that in hyperthyroid rabbits, the left ventricle has decreased contractile efficiency and increased energy cost of excitation-contraction coupling and that the decreased contractile efficiency in hyperthyroid hearts is probably due to the increased V1/V3 ratio of the myosin isoform component. In addition, this study demonstrates that the VO2-PVA and VO2-FTI relations dissociate depending on the intervention, even in the same isovolumic contraction mode.This publication has 34 references indexed in Scilit:
- Influence of ventricular contractility on non-work-related myocardial oxygen consumptionHeart and Vessels, 1987
- Tension-pCa relations of saponin-skinned rabbit and human heart muscleJournal of Molecular and Cellular Cardiology, 1986
- The economy of isometric force development, myosin isoenzyme pattern and myofibrillar ATPase activity in normal and hypothyroid rat myocardium.Circulation Research, 1985
- Normalization of end-systolic pressure-volume relation and emax of different sized hearts.Japanese Circulation Journal, 1984
- The effects of muscle length on intracellular calcium transients in mammalian cardiac muscle.The Journal of Physiology, 1982
- Functional significance of altered myosin adenosine triphosphatase activity in enlarged heartsThe American Journal of Cardiology, 1979
- Isoprenaline, propranolol, and the energy output of rabbit cardiac muscleCardiovascular Research, 1972
- Energy Production in Cardiac Isotonic ContractionsThe Journal of general physiology, 1970
- Influence of the thyroid state on left ventricular tension-velocity relations in the intact, sedated dogJCI Insight, 1969
- Influence of the Thyroid State on the Intrinsic Contractile Properties and Energy Stores of the Myocardium*JCI Insight, 1967