Transmural differences of lipofuscin pigment accumulation in the left ventricule of rat heart during growth and aging.

In view of the higher metabolic rate in subendocardial heart tissue, the rate of age-related lipofuscin pigment accumulation was explored in different regions of the left ventricle heart wall of Sprague-Dawley rats. Hearts were removed from 2-, 6-, 12- and 24-month-old rats, and lipofuscin pigment accumulation was assessed in the subepicardial and subendocardial layers, either by measuring extractable fluorescent material, or by direct visualization with fluorescence microscopy. Findings showed that the amount of extractable fluorescent material and the number, size and brightness of the fluorescent lipofuscin granules increased with age in all the myocardial tissue layers. The rate of accumulation of extractable fluorescent material was higher in subendocardial compared to subepicardial tissue. At the microscope, fluorescent granules exhibited a different morphological appearance in the subendocardial and subepicardial tissue of the two older age-groups. These data support the hypothesis that liposoluble age-pigment deposition is linked to the rate of local oxidative metabolism.