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Chronic -agonist administration affects cardiac function of adult but not old rats, independent of -adrenoceptor density

¹Department of Physiology, The University of Melbourne, Melbourne, Victoria; and ²School of Agriculture, Charles Sturt University, Wagga Wagga, New South Wales, Australia

Submitted 13 December 2004 ; accepted in final form 18 February 2005

Although -adrenoceptor agonists have clinical merit for attenuating the age-related loss of skeletal muscle mass and strength (sarcopenia), potential cardiac-related side effects may limit their clinical application. The aim of this study was to determine whether chronic -agonist administration impairs cardiac function in adult or aged rats. Adult (16 mo) and aged (28 mo) Fischer 344 rats were treated with fenoterol (1.4 mg·kg^–1·day^–1 ip) or vehicle for 4 wk. Heart function was assessed in vitro before analyses of cardiac structure and -adrenoceptor density. Heart mass increased 17% and 25% in fenoterol-treated adult and aged rats, respectively. The increased heart mass in aged, but not adult, rats was associated with a relative increase in collagen content. Cardiac hypertrophy in adult rats was associated with an increase in left ventricular developed pressure, a marked reduction in cardiac output, and a reduction in coronary flow per unit heart mass. In contrast, negligible differences in ventricular function were observed in fenoterol-treated aged rats. The differential effect on contractile function was not associated with age-related differences in -adrenoceptor density but, rather, an age-related increase in downregulation after treatment. Our results show that chronic -agonist treatment impairs cardiac function to a greater extent in adult than in aged rats. These results provide important information regarding the potential effects of chronic -agonist use on cardiac function and the future development of safe and effective treatments for sarcopenia.

adrenergic agonists; aging; hypertrophy; ventricular function; receptors

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