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1 Department of Cardiovascular Division, Department of Internal Medicine, Washington University School of Medicine, Saint Louis, MO, USA
2 Division of Radiological Sciences, Edward Mallinkrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, MO, USA
3 Division of Biostatistics, Washington University School of Medicine, Saint Louis, MO, USA
4 Department of Cardiovascular Division, Department of Internal Medicine, Washington University School of Medicine, Saint Louis, MO, USA; Division of Radiological Sciences, Edward Mallinkrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, MO, USA
* To whom correspondence should be addressed. E-mail: sotop{at}mir.wustl.edu.
Under resting conditions there is an age-related decrease in myocardial fatty acid utilization (MFAU) and oxidation (MFAO) and a relative increase in myocardial glucose utilization (MGU). The impact of age on the myocardial metabolic response to catecholamines is not well defined. Sixteen younger (mean age 26 ± 5 years) and 14 older volunteers (mean age 69 ± 4 years) underwent positron emission tomography in order to measure myocardial blood flow, myocardial oxygen consumption (MVO2), MFAU, MFAO and MGU both under resting conditions and during dobutamine infusion. In response to dobutamine, the rate-pressure product, myocardial blood flow and MVO2 increased by similar amounts in both groups. No age-related differences were noted in the plasma insulin, glucose, fatty acid or lactate response to dobutamine. With dobutamine, MFAU and MFAO increased by a similar extent in both young and older volunteers (age/DOB interaction: p = 0.62, 0.75 respectively). In contrast, MGU increased with dobutamine in the younger (from 149 ± 71 to 209 ± 78 nmol.g-1.min-1, p = 0.04), but not in the older group (from 235 ± 147 to 176 ± 84 nmol.g-1.min-1, p = 0.23; age/DOB interaction: p = 0.03). With dobutamine, hearts in both young and older volunteers respond by increasing their MFAU and MFAO. While younger hearts also respond with an increase in MGU, older hearts do not. Although the clinical significance of these findings awaits further study, they may partially explain the impaired contractile reserve and the increased incidence of cardiovascular disease in older individuals.
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