Ultrastructural changes of collagen fibers in the anterior cruciate ligament of bipedal rats after enforced running.

: The effect of enforced running on the morphological characteristics of the fibroblasts and on the distribution of the collagen fibril diameter in the anterior cruciate ligament of bipedal rats was examined by electron microscopy. Twelve bipedal rats were divided into two groups of equal numbers: (1) those without exercise, and (2) those with enforced exercise on a treadmill for four weeks. Ninety percent of the fibroblasts in the rats without exercise were ovoid-shaped with a round nucleus, whereas eighty-one percent of those in the rats with exercise were spindle-shaped with indented nucleus. There was a significant difference in the ratios of ovoid-shaped to spindle-shaped cells between the two groups (p < 0.05). There was an increased number of rough surfaced endoplasmic reticula and lysosomal vesicles in the fibroblasts of the rats with exercise. The collagen fibril diameters of the rats with exercise varied in size from 20 to 120 nm, while those of the rats without exercise were uniform in size, mostly between 50-80 nm. Mean collagen fibril diameter was 70.8 +/- 16.6 nm in the rats without exercise, and 66.6 +/- 21.9 nm in the exercised rats. This difference was significant (p < 0.05). These electron-microscopical findings indicate an increased collagen metabolism in the anterior cruciate ligament of rats with enforced running.