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

The effects of endurance run training on oc-adrenergic responsiveness of ra t left ventricle (LV) were examined in cardiomyocytes and isovolumic LV. Fe male 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 mu M phenylephrine (PE) while paced at 0.5 Hz in 2 mM extracellular Ca2+ concentration at 29 degre es C. Cardiomyocyte shortening and shortening velocity increased with PE, a nd these effects were more pronounced in the Sed group. The rate of cytosol ic Ca2+ concentration removal was reduced by PE in the Sed cardiomyocytes, but was unaffected in the Tr. Isovolumic LV pressure was recorded immediate ly before and during 5-min perfusion with 5 mu M PE during pacing at 280 be ats/min and 37 degrees C, and positive inotropy due to PE was more pronounc ed in the Sed than in the Tr. These data demonstrated that the effects of a lpha-adrenergic stimulation on myocardial positive inotropy and calcium reg ulation were reduced in this rat model of run training at both the cellular and whole organ levels.