Effect of Age on the Collagen Content of the Normal Rat Myocardium

Abstract The development of the collagenous tissue in the myocardium was studied in rats aged one day to 18 months. During the first three weeks a rapid exponential increase of both the heart weight and the total amount of myocardial hydroxyproline occurred, although the concentration of total and insoluble hydroxyproline as estimated per mg of dry tissue showed no significant change. Thereafter the growth rates of the heart weight and total and insoluble hydroxyproline fell with increasing age. The growth rate of total hydroxyproline fell more slowly, however, and a slight increase in the content of total and insoluble hydroxyproline per dry tissue was noted with increasing age. The proportion of neutral salt‐soluble collagen hydroxyproline in the myocardium dropped from an initial value of 30 per cent of the total hydroxyproline in newborn rats to 10 per cent at the age of three weeks. After this the proportion of soluble hydroxyproline remained almost unchanged. At the same time the proportion of free hydroxyproline dropped from 25 per cent of the total hydroxyproline in newborn rats to 1.3 per cent at the age of 6 months. The results seem to suggest that during the postnatal period insoluble mature collagen develops rapidly, and therefore with increasing age constitutes a slowly rising proportion of the myocardial collagenous framework. This seems to be a response to the functional demand on the growing heart for increased tensile strength.