Effect of ageing and malnutrition on rat myocardium. II. The microvasculature.

The modulating effects of ageing and malnutrition on rat myocardium were studied morphometrically with respect to the microvasculature. An increase in capillary density together with a decrease in capillary lumen cross-sectional area was noted during starvation. The important changes seen in the myocyte T-system were paralleled by a decreased diffusion distance for oxygen from the capillary lumen to the mitochondrion. The changes described in the aged rat heart point to an altered inter-relationship between parenchyma and vascularization with a lower capillary volume fraction and a greater diffusion distance from the capillary lumen to the mitochondrion; this is caused by hypertrophy of the aged myocyte. This reduction in capacity to exchange substrates is further reduced by the less developed T-system in the older myocyte.