Journal article
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
Circulation research, Vol.66(4), pp.999-1011
04/1990
Handle:
https://hdl.handle.net/2376/118258
PMID: 2317899
Abstract
Both systolic pressure-volume area (PVA) and force-time integral (FM1) have been used as measures of oxygen consumption per beat ( 2) in the isolated left ventricle. The reciprocal of the slope of the 2-PVA relation has been considered to reflect the chemomechanical energy transduction efficiency of the contractile machinery (contractile efficiency), whereas its 2 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 2-PVA and 2-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 (Eʼmax, ventricular contractility index) were similar for normal and hyperthyroid groups. However, the slopes and 2 intercepts of the 2-PVA and 2-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 2 for excitation-contraction coupling (0.028±0.004 ml O2/beat/100g) 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 β-adrenoceptors because isoproterenol did not affect the slope of the 2-PVA relation in all groups. In contrast, the slope of the 2-FTI relation was significantly increased by isoproterenol in all groups. Neither the 2-PVA nor the 2-FTI relations in hypothyroid hearts were different from those in normal hearts except for significantly lower 2 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 2-PVA and 2-FTI relations dissociate depending on the intervention, even in the same isovolumic contraction mode.
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Details
- Title
- 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
- Creators
- Yoichi Goto - Cardiology Unit, Department of Medicine, University of Vermont, Burlington, VermontBryan SlinkerMartin LeWinter
- Publication Details
- Circulation research, Vol.66(4), pp.999-1011
- Academic Unit
- Integrative Physiology and Neuroscience, Department of
- Publisher
- American Heart Association, Inc
- Identifiers
- 99900548282501842
- Language
- English
- Resource Type
- Journal article