Effects of Exercise Training on Biochemical and Biomechanical Properties of Rat Aorta

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Abstract
The authors studied the effect of prolonged physical exercise on the mechanical properties of rat aorta in relation to the amounts and qualities of arterial connective tissue fibrous proteins. Twelve male rats were divided into two groups: 6 sedentary rats (S) and 6 training rats (T), which were forced to swim from nine weeks to twenty-five weeks of age. The ultimate tensile stress and the ultimate tensile extension ratio of ring specimens at the descending thoracic aorta were larger in T than in S (192.3 ± 47.9 g/mm2, mean ± SD, vs 147.8 ± 26.0, p < 0.05; 3.52 ± 0.13 vs 3.18 ± 0.27, p < 0.05; respectively). The elasticity parameter, calculated by fitting stress-strain curves to exponential function in the stress level of 0-20 g/mm2, was lower in T than in S (1.79±0.15 vs 2.13±0.24, p < 0.01). The contents of elastin (alkali-insoluble elastin preparation) and collagen were higher in T than in S (0.44 ± 0.11 g/g dry aorta vs 0.30 ± 0.06, p < 0.05; 0.15 ± 0.04 g/g dry aorta vs 0.11 ± 0.04, NS, respectively). Although the aortic calcium content did not significantly change in the training rats (T 1.17 ± 0.23 mg/g dry aorta, S 0.95 ± 0.34), the content of calcium in elastin was lower in T than in S (1.75 ± 0.51 mg/g dry elastin vs 2.63 ± 1.00, p < 0.05). Elastin isolated from the training rats showed significant decreases in some of the polar amino acids: arginine (3.18±1.00 residues/1000 residues vs 4.12 ± 0.40, p < 0.05), threonine (6.79 ± 1.91 vs 8.69 ± 1.51, p < 0.05), and serine (9.66 ± 1.56 vs 11.97± 1.41, p < 0.05). The authors conclude that prolonged physical exercise from an early age provides training rat with a strong and extensible aorta, which is related to the larger amount of elastin with probably fewer degenerative changes.