Increased contractile potential of papillary muscles from exercise-trained rat hearts.
Female rats (n = 24) swam 6 h/day, 5 days/wk, for over 6 wk. Training increased both wet and dry weight of ventricles 15% above control. The active length-tension curve for trained left ventricular papillary muscles (LVPM) was elevated, with maximum tension (Tmax) at optimal length 37% higher than that of untrained LVPM. Training did not alter passive length-tension, time-to-peak tension (TPT), or half-relaxation time (1/2RT). The maximum rate of tension development (dT/dt), however, was increased 22% by training. The force-velocity curve of trained LVPM was shifted upward; both estimated Vmax and the minimum isometric load where shortening equals zero were greater than control. Exogenous isoproterenol (5.8 nM) did not affect Tmax but significantly decreased TPT and 1/2RT to the same extent for both groups of muscles. Maximum dT/dt was increased to a greater extent by isoproterenol for trained LVPM. These findings indicate hearts hypertrophied by exercise have an increased contractile potential per unit of myocardial mass.
D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006321:Heart / Q000033:anatomy & histology; D006352:Heart Ventricles; D009129:Muscle Tonus; D009200:Myocardial Contraction; D009929:Organ Size; D010210:Papillary Muscles / Q000502:physiology*; D010805:Physical Conditioning, Animal; D051381:Rats