Ultrastructural cytology of regenerating tendon--an experimental study.

Cellular differentiations in regenerating tendon tissue of rats and guinea pigs were examined by the aid of the electron microscope. Fibroblasts with certain variations were found as basic cell types. Corresponding to the organelle composition classical fibroblasts, fibroblasts with histiocyte-like features and fibroblasts with myoide differentiations (comparable to the so-called myofibroblasts) were identified. Furthermore, proliferating capillaries with remarkable pericytic activities among other things producing fibroblast-like features must be mentioned. This fact led to the conclusion, that a part of fibroblasts in the proliferating connective tissue during tendon repair may derive from pericytes. Our ultrastructural investigations showed proof of the great plasticity of fibroblasts which function as stem cells in connective tissue regeneration.