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Regulation of murine myocardial energy metabolism during adrenergic stress studied by in vivo ³¹P NMR spectroscopy

¹Department of Radiology, Division of Magnetic Resonance Research, The Johns Hopkins University School of Medicine, Baltimore 21205; and ²Department of Medicine, Division of Cardiology, The Johns Hopkins Hospital, Baltimore, Maryland 21287

Submitted 22 May 2003 ; accepted in final form 10 July 2003

Image-guided, spatially localized ³¹P magnetic resonance spectroscopy (MRS) was used to study in vivo murine cardiac metabolism under resting and dobutamine-induced stress conditions. Intravenous dobutamine infusion (24 µg · min^–1 · kg body wt^–1) increased the mean heart rate by 39% from 482 ± 46 per min at baseline to 669 ± 77 per min in adult mice. The myocardial phosphocreatine (PCr)-to-ATP (PCr/ATP) ratio remained unchanged at 2.1 ± 0.5 during dobutamine stress, compared with baseline conditions. Therefore, we conclude that a significant increase in heart rate does not result in a decline in the in vivo murine cardiac PCr/ATP ratio. These observations in very small mammals, viz., mice, at extremely high heart rates are consistent with studies in large animals demonstrating that global levels of high-energy phosphate metabolites do not regulate in vivo myocardial metabolism during physiologically relevant increases in cardiac work.

dobutamine stress; cardiac metabolism; magnetic resonance spectroscopy; PCr-to-ATP ratio

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