Age-related changes in cardiac muscle of rat.

Study of the age-related changes in cardiac muscle of 5, 10, 15, 20, and 25 months old albino rats showed that the muscle mass decreased by 10% while the ratio of the weight of cardiac muscle to body weight decreased by 30% between 5 and 25 months. Autolytic and proteolytic activity of sarcoplasmic proteins increased remarkably (70% and 200%, respectively) between 5 and 25 months of age. Although the total protein content decreased, the amount of fibrous protein (collagen) increased by 50%. Levels of salt soluble and labile collagen (free hydroxyproline released at 65 degrees C in Ringer solution) decreased by 65% and 50%, respectively, while insoluble collagen increased by 180% with advance in age from 5 to 25 months. Increase in acid soluble collagen was seen only up to 20 months of age. The acid mucopolysaccharide content decreased, whereas the activity of beta-glucuronidase showed an increase from 110-148 units between 10 and 15 months of age. beta-N-acetylglucosaminidase increased by 25% as the age increased from 5 to 25 months.