The time dependence of training-induced increase in skeletal muscle capillarization and the spatial capillary to fibre relationship in normal and neovascularized skeletal muscle of rats.

One hundred and eighty-four rats of different ages were investigated regarding the basic capillary-fibre array and the array resulting from capillary proliferation induced by swimming training and dipyridamole treatment. The time dependence of the training-induced capillary increase in the muscle was also investigated. Sections of the medial portion of the quadriceps femoris muscle were evaluated in light microscope for total capillarization, fibre area and fibre type composition. After 4 and 8 weeks of swimming training, increases in capillary density, capillary to fibre ratio and mean number of capillaries in contact with each fibre were recorded. No changes in muscle fibre area or fibre composition were seen. In all groups the majority of the capillaries was in contact with three muscle fibres. The capillary proliferation induced by training and dipyridamole treatment was confined to the capillaries in contact with two and three fibres. The results indicate a basic hexagonal capillary-fibre array with a possible position for a capillary in each corner of the hexagon. This pattern is retained in the increased vascularity induced by swimming training and dipyridamole treatment.