Aging and hydroxproline content in human heart muscle

Hydroxproline content was chemically determined in 45 human hearts obtained at autopsy, in order to know possible correlations between aging and hydroxyproline content in the heart muscle. There were no significant differences in the mean total hydroxyproline content between the epicardium and the endocardium, between left and right ventricles, nor between young, middle and old age groups. The hydroxyproline content in NaCl-soluble fraction decreased, and that in TCA-soluble fraction and in residue fraction increased with age. There were significant differences in the mean hydroxyproline content in NaCl-soluble fraction between middle and old age groups, and in residue fraction between young and old age groups in the endocardium of the left ventricle. Accordingly, the ratio of the content in NaCl-soluble fraction to that in TCA-soluble fraction decreases with age. This tendency was more evident in the epicardium than in the endocardium on the left ventricle. These results indicate that total hydroxyproline content per 1 mg of lyophilized material does not show any quantitative changes, but does show qualitative changes with age.