Ultrastructural morphometry of membrane-bound intracytoplasmic collagen fibrils in tendon fibroblasts exposed to He:Ne laser beam.

Collagen fibrils are not found in fibroblast cytoplasm except in certain pathological conditions or in the presence of drugs and other agents that accelerate collagen turnover. Because low energy laser photostimulation is both a non-pathogenic and non-chemical accelerator of collagen synthesis, its effects were studied on four groups of calcaneal tendons from 18 rabbits (1) to test the hypothesis that vacuolar fibrils are not produced exclusively by diseases and chemical agents, and (2) to compare the morphometry of matrical and vacuolar fibrils. The right calcaneal tendons of nine rabbits were surgically tenotomized and repaired; six of these were transcutaneously irradiated with He:Ne laser everyday. The right calcaneal tendon of six of the remaining nine rabbits were similarly irradiated with laser, but without prior tenotomy and repair. 21 days later, all tendons were fixed in situ and processed for electron microscopy. Fibril-bearing vacuoles were found only in fibroblasts of tenotomized laser-irradiated tendons. Similar vacuoles were not seen in non-tenotomized laser-irradiated tendons nor in non-irradiated tendons whether tenotomized or not. Mann-Whitney U tests revealed no statistically significant differences in the cross-sectional areas or diameters of matrical and vacuolar fibrils. These findings suggest (a) that matrical and vacuolar fibrils have a common origin, and (b) that vacuolar fibrils can be induced by a non-pathologic, non-chemical accelerator of collagen synthesis.