Investigations on connective tissue metabolism: ageing of the human heart

In any given phase of the age process, the rates of synthesis and degradation of collagen and other macromolecules are diversely influenced by changes in the respective enzyme activities. This naturally affects and reflects the contents of the intracellular as well as extracellular macromolecules. In our studies, the total contents of desoxyribonucleic acid (DNA), hydroxyproline, hexosamines and uronic acids of the four compartments of the human heart were estimated and plotted against age. The results obtained for DNA showed an initial rapid decline in its content to about the middle of the third decade of life, i.e. around the end of the maturation period. Thereafter, the DNA curves showed a relatively slower decrease until the fifth decade, after which a slight increase was observed during senescence. This holds for both the left and the right sides of the heart. Hydroxyproline levels, on the other hand, remained unchanged in all the different compartments except in the left atrium, where the initial phase of the curve showed a significant drop until the middle of the fourth decade. Hydroxyproline values in the atria were twice as high as in the ventricles, which in turn showed higher levels of hexosamines than uronic acids. Both hexosamines and uronic acids in the atrial walls showed an initial decline followed by a gradual rise during ageing. Contents of uronic acids in the ventricles showed a gradual but steady rise throughout life.