Exercise training improves lusitropy by isoproterenol in papillary muscles from aged rats.
Aging is associated with a decreased cardiac responsiveness to beta-adrenergic stimulation. We examined the effect of endurance exercise training of old Fischer 344 male rates on beta-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 beta-adrenergic stimulation, there were no group differences for peak tension, maximum rate of tension development (+dP/dt), or maximum rate of tension dissipation (-dP/dt). 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 beta-adrenergic stimulation by isoproterenol of peak tension, -dP/dt, time to peak tension, or contraction duration. The inotropic response (+dP/dt) 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.
Section of Cardiovascular Sciences, Baylor College of Medicine, Houston, Texas 77030, USA.
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Taffet
L A
LA
Michael
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CA
Tate
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology; D010805:Physical Conditioning, Animal; D051381:Rats; D011916:Rats, Inbred F344
D000318:Adrenergic beta-Agonists; D007545:Isoproterenol; D002118:Calcium