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Am J Physiol Heart Circ Physiol 277: H2136-H2144, 1999;
0363-6135/99 $5.00
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Vol. 277, Issue 6, H2136-H2144, December 1999

Chronic run training suppresses alpha -adrenergic response of rat cardiomyocytes and isovolumic left ventricle

Bradley M. Palmer1, M. Charlotte Olsson1, Joshua M. Lynch1, Lisa C. Mace1, Steven M. Snyder1, Scott Valent2, and Russell L. Moore1,2

1 Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder 80309; and 2 Cardiology Division, University of Colorado Health Sciences Center, Denver, Colorado 80262

The effects of endurance run training on alpha -adrenergic responsiveness of rat left ventricle (LV) were examined in cardiomyocytes and isovolumic LV. Female Sprague-Dawley rats were sedentary (Sed) or trained (Tr) for >20 wk by treadmill running. Cardiomyocyte shortening and fura 2 fluorescence ratio were recorded before and during 5-min exposure to 5 µM phenylephrine (PE) while paced at 0.5 Hz in 2 mM extracellular Ca2+ concentration at 29°C. Cardiomyocyte shortening and shortening velocity increased with PE, and these effects were more pronounced in the Sed group. The rate of cytosolic Ca2+ concentration removal was reduced by PE in the Sed cardiomyocytes, but was unaffected in the Tr. Isovolumic LV pressure was recorded immediately before and during 5-min perfusion with 5 µM PE during pacing at 280 beats/min and 37°C, and positive inotropy due to PE was more pronounced in the Sed than in the Tr. These data demonstrated that the effects of alpha -adrenergic stimulation on myocardial positive inotropy and calcium regulation were reduced in this rat model of run training at both the cellular and whole organ levels.

phenylephrine; propranolol; phentolamine; fura 2


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