The possible transport and exclusion mode of lipofuscin in rat myocardium under electron microscopy

Lipofuscin accumulation has been observed in human coronary arteries but whether or not myocardial tissue can release lipofuscin generated within cardiomyocytes must be clarified, as this may provide indicators for future anti-ageing research. The hearts of Sprague Dawley rats, aged 6-24 months, were embedded in resin and ultrathin sections cut for electron microscopy. Lipofuscin granules were abundant in cardiomyocytes. Cardiomyocytes were seen to release lipofuscin granules into the myocardial interstitium as cytoplasmic fragments with irregular protrusions on the sarcolemma surface. The cytoplasmic fragments entering the stroma fused directly with the endothelial cells of adjacent capillaries, delivering lipofuscin to the vessel wall. These fragments were also seen to be engulfed by stromal macrophages or fused with fibroblasts, which then combined with capillary endothelial cells to deliver lipofuscin to the vessel wall. Some cytoplasmic fragments disaggregated and formed membrane-like waste, which travelled to the vessel wall from the myocardial stroma as soluble fine particles via diffusion or pinocytosis of capillary endothelial cells. Lipofuscin entered the vascular wall and endothelial cells, forming large and small protrusions or folds that transported the lipofuscin to the vascular lumen and bloodstream.