Regional adaptations in three rat tendons

Although detailed histological and immunocytochemical studies have been pub lished for the rat calcanear tendon (CT), little is known of the structure, composition and biomechanics of the deep (DFT) and superficial (SIFT) flex or tendons. In this study, we examined the structural specialization of the se three tendons in 90-day-old rats by applying histochemical and biochemic al assays to different tendon regions (proximal, intermediate and distal re gions of the DFT and SFT, and proximal and distal regions of the CT). There were regional differences in tissue structure, glycosaminoglycan type and content, swelling properties and in the amount and distribution of elastic fibers. Dermatan sulfate occurred in all regions, but chondroitin sulfate p redominated in the intermediate region of the DFT and in the distal region of the CT. These two chondroitin sulfate-bearing regions showed swelling in water, while all other regions lost fluid in water. Fibrocartilaginous sit es were observed on the CT, one at the insertion to the bone and another di stally at the innermost area of the tendon. The intermediate region of the DFT showed round cells disposed in lacunae, while the proximal and distal r egions were typically fibrous: The intermediate region of the SFT showed a wavy array of Collagen bundles but neither toluidine blue staining in the m atrix nor round cells. Elastic fibers were present in each region of the th ree tendons, but were more prominent in the intermediate zone of the SFT. T hese results demonstrate regional variation in the three tendons. Tendon di fferentiation may occur by an increase in the number of elastic fibers and by variations in the arrangement of Collagen fibers, without fibrocartilage formation. (C) 2001 Harcourt Publishers Ltd.