OBJECTIVE: The pathogenesis of osteoarthritis centers on the imbalance between catabolic and anabolic processes in cartilage metabolism. Insulin growth factor 1 (IGF-1) has been shown to have anabolic effects in cartilage in vitro. This study aim to determine whether IGF-1 on cartilage is associated with loss of chondrocyte and extracellular matrix breakdown using the Hartley guinea pig model. MATERIALS AND METHODS: Cartilage from the medial and lateral tibial plateau of 6-month and 12-month old Hartley guinea pigs were used for this study. Histological analysis was performed with hematoxylin-eosin (HE) and toluidine blue staining. Safranin-O staining was used to quantify proteoglycan (PG) loss and the extent of cartilage damage by Modified Mankin score. Distribution of IGF-1 was demonstrated with in situ hybridization techniques. IGF-1 mRNA levels were assessed using Real-time PCR. RESULTS: Histological loss of chondrocytes, and cartilage matrix and decreased IGF-1 distribution were demonstrated in a temporal and spatial manner. Compared to the 6-month old samples, the 12-month specimens had significantly cartilage degeneration and less cartilage matrix and PGs staining. Decreased level of IGF-1 was also observed in the 12-month samples. These observations were more pronounced in the medial tibial plateau when compared to the lateral plateau. CONCLUSIONS: The decreased level of IGF-1 may play a critical role for maintaining the balance between catabolic and anabolic processes in cartilage metabolism during the development of osteoarthritis. Thus, the increase of IGF-1 may be applicable to developing OA therapy.