H Kiriazis1, C L Gibbs. 1. Department of Physiology, Monash University, Clayton, 3168, Victoria, Australia.
Abstract
OBJECTIVES: This study aimed to investigate the effect of aging on the work output and efficiency of rat papillary muscle. METHODS: The mechanical and energetic properties of left ventricular papillary muscle preparations isolated from 6-, 15-, and 27- to 32-month-old Sprague-Dawley rats were measured in myothermic experiments at 27 degrees C at a stimulus frequency of 0.167 Hz. RESULTS: We found that the basal metabolism measured in quiescent papillary muscles was significantly reduced in the 27- to 32-month-old group (4.9 mWg(-1) compared to 7.7 and 7.0 mWg(-1) in the 6- and 15-month groups). In isotonic experiments, the work output (at a range of afterloads) was significantly depressed for the 27- to 32-month group being only 52% of the work output of the 6-month group. This outcome was due to a decrease in both the extent of muscle shortening only, 66% of 6- and 15-month data, and in the maximum force developed. The reduced work was accompanied by a parallel decrease in energy consumption (enthalpy) and hence, the net mechanical efficiency (work/active enthalpyx100%) was not altered. A force-length- area (FLA) analysis was applied to the isotonic data and an energy: FLA regression line was obtained for each preparation. We found that there were no significant differences in either the intercept or slope of the energy: FLA relation with age. Contractile efficiency (39+/-3%) in the 27- to 32-month group was not significantly different to that found in the 6-month (43+/-4%) or 15-month (40+/-3% group). CONCLUSION: There are no changes in the mechanical performance or efficiency of cardiac muscle from young (6-month-old) or adult (15-month-old) rats but in the aged and senescent rats (27-32-month-old) there is a pronounced decline in stress development and shortening ability leading to a fall in work output. Mechanical and contractile efficiency however remain unchanged in old age and the data resembles that obtained in pressure overload hypertrophy.
OBJECTIVES: This study aimed to investigate the effect of aging on the work output and efficiency of rat papillary muscle. METHODS: The mechanical and energetic properties of left ventricular papillary muscle preparations isolated from 6-, 15-, and 27- to 32-month-old Sprague-Dawley rats were measured in myothermic experiments at 27 degrees C at a stimulus frequency of 0.167 Hz. RESULTS: We found that the basal metabolism measured in quiescent papillary muscles was significantly reduced in the 27- to 32-month-old group (4.9 mWg(-1) compared to 7.7 and 7.0 mWg(-1) in the 6- and 15-month groups). In isotonic experiments, the work output (at a range of afterloads) was significantly depressed for the 27- to 32-month group being only 52% of the work output of the 6-month group. This outcome was due to a decrease in both the extent of muscle shortening only, 66% of 6- and 15-month data, and in the maximum force developed. The reduced work was accompanied by a parallel decrease in energy consumption (enthalpy) and hence, the net mechanical efficiency (work/active enthalpyx100%) was not altered. A force-length- area (FLA) analysis was applied to the isotonic data and an energy: FLA regression line was obtained for each preparation. We found that there were no significant differences in either the intercept or slope of the energy: FLA relation with age. Contractile efficiency (39+/-3%) in the 27- to 32-month group was not significantly different to that found in the 6-month (43+/-4%) or 15-month (40+/-3% group). CONCLUSION: There are no changes in the mechanical performance or efficiency of cardiac muscle from young (6-month-old) or adult (15-month-old) rats but in the aged and senescent rats (27-32-month-old) there is a pronounced decline in stress development and shortening ability leading to a fall in work output. Mechanical and contractile efficiency however remain unchanged in old age and the data resembles that obtained in pressure overload hypertrophy.
Authors: J-C Han; A J Taberner; K Tran; S Goo; D P Nickerson; M P Nash; P M F Nielsen; E J Crampin; D S Loiselle Journal: J Appl Physiol (1985) Date: 2012-08-09
Authors: Nikita M Patel; Ze-Wei Tao; Mohamed A Mohamed; Matt K Hogan; Laura Gutierrez; Ravi K Birla Journal: ASAIO J Date: 2015 Jan-Feb Impact factor: 2.872