Repeated development and regression of exercise-induced cardiac hypertrophy in rats

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Abstract
Adult female rats were exercised by swimming 6 h/day, 6 days/wk for 3 wk. This was followed by a detraining period of inactivity of 50 days. Subsequently the animals underwent 2 additional 4-wk periods of swimming and two 50-day periods of detraining. Following each training phase, both wet and dry ventricular weights were increased between 19 and 29% above those of the sedentary controls. Ventricular weights of the exswimmers returned within control levels after each detraining phase. The activity of citrate synthase, a mitochondrial marker and myoglobin concentration remained relatively constant in ventricular muscle of all groups. Hydroxyproline, a collagen marker, decreased in concentration as ventricular weight increased after each training phase and increased as a ventricular weight regressed in detraining. There was an overall pattern for total hydroxyproline per heart to be 10-12% higher in the swimmers-exswimmers than in the controls throughout each training-detraining phase, but these effects were not statistically significant. Apparently, the development and regression of cardiac hypertrophy are reversible with successive phases of training detraining, and the accumulation of collagen does not become additive with repeated changes in cardiac size.