Exercise training improves lusitropy by isoproterenol in papillary muscles from aged rats

Abstract

Taffet, George E., Lloyd A. Michael, and Charlotte A. Tate.Exercise training improves lusitropy by isoproterenol in papillary muscles from aged rats. J. Appl. Physiol. 81(4): 1488–1494, 1996.—Aging is associated with a decreased cardiac responsiveness to β-adrenergic stimulation. We examined the effect of endurance exercise training of old Fischer 344 male rats on β-adrenergic stimulation of the function of isolated left ventricular papillary muscle. Three groups were examined: sedentary mature (SM; 12-mo old), sedentary old (SO; 23–24 mo old), and exercised old (EO; 23–24 mo old) that were treadmill trained for 4–8 wk. The isometric contractile properties were studied at 0.2 Hz and 0.75 mM calcium. Without β-adrenergic stimulation, there were no group differences for peak tension, maximum rate of tension development (+dP/d t), or maximum rate of tension dissipation (−dP/d t). The time to peak tension was longer ( P < 0.05) for both EO and SO than for SM rats. Half relaxation time (RT1/2) was prolonged ( P < 0.05) for SO compared with SM and EO (which did not differ). The three groups did not differ in the β-adrenergic stimulation by isoproterenol of peak tension, −dP/d t, time to peak tension, or contraction duration. The inotropic response (+dP/d t) of SM was greater ( P < 0.05) than that in SO or EO rats (which did not differ); however, the lusitropic response (RT1/2) was lesser ( P < 0.05) in SO than in SM or EO rats (which did not differ). Thus exercise training of old rats improved the lusitropic response to isoproterenol without altering the age-associated impairment in inotropic response.