Effects of tensile forces on the expression of type III collagen in rat interparietal suture

The aim was to investigate the direct contribution of mechanically induced stress to synthesized type III collagen in the interparietal suture. Twenty 4-week-old male rats were used as experimental animals. An activated expansion spring was placed across the interparietal suture. After expansion, the parietal bones including the suture were dissected and immunostained for type I and III collagens. Also, a three-dimensional model of the interparietal suture was developed to analyze stress during expansion. The localization of type III collagen in the suture was dependent upon the duration of expansion. Although the control suture exhibited no or little reactivity for type III collagen, it was observed as early as 15 h of expansion in the cambial layers, and was distributed throughout the suture at 50 h of expansion. The time-dependent distribution of type III collagen was fully consistent with that of tensile stresses calculated by the use of a three-dimensional finite-element model. It was concluded that the increases in tensile stress are associated with the synthesis of type III collagen in the suture.