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Intermittent cardiac overload

n this issue of The Journal of Physiology, a group of researchers form Portugal performed a study to address the question of whether submitting the heart to intermittent and tolerable amounts of stress, independent of its nature, could induce a cardiac phenotype that would fit within the ‘physiological’ spectrum To answer their question the authors compared three groups of animals: (1) Sedentary+Placebo, (2) Exercise, and (3) Sedentary+Dobutamine (simulated exercise: similar haemodynamic demand to the exercise group). Following an 8 week protocol, the authors collected data at rest and during cardiac overload induced by banding of the aorta. The exercise and simulated exercise groups had lower body weight, faster cardiac relaxation, cardiomyocyte hypertrophy, and improved mitochondrial complex IV and V activity. The latter finding is of particular importance because it can indicate an enhanced capacity to support cardiomyocyte energetic cost without compromising the ATP that is needed to maintain intracellular homeostasis.

In summary, the authors’ results show that regardless of the nature of the controlled intermittent cardiac overload the heart responds favourably and undergoes adaptive hypertrophy. Importantly, the adaptive and ‘physiological’ hypertrophy in both the exercise and simulated exercise groups protected against an acute pressure overload insult. In conclusion, I am in full agreement with the authors’ statement that we need further research to fully elucidate why some cardiac overloading stimuli are beneficial while others are deleterious.