EFFECTS OF INSULIN AND INSULIN-LIKE GROWTH-FACTOR-I AND GROWTH-FACTOR-II ON THE GROWTH OF EQUINE FETAL AND NEONATAL CHONDROCYTES

The effects of insulin and insulin-like growth factors (IGFs) I and II on fetal and foal chondrocytes were investigated in vitro. Chondrocyt es from the lateral trochlear ridge of the distal femur were obtained from 2 fetuses (280 and 320 days gestation) and one 4-day-old foal and cultured, Membrane proteins consistent with type 1 and type 2 IGF rec eptors were demonstrated by radioligand cross linking and equilibrium binding analysis, It was demonstrated that both IGF-I and IGF-II acted as mitogens for isolated equine chondrocytes when present as the sole mitogenic factor in monolayer culture, It was further shown that wher eas insulin was able to promote the survival and expansion of cell pop ulations of chondrocytes in culture there was significantly reduced mi togenic stimulation compared to the IGFs, These results suggest that t he role of insulin in growth cartilage may be to promote chondrocyte s urvival, or to suppress differentiation/apoptosis. This supports the h ypothesis that relative hyperinsulinaemia may be a contributory factor to equine dyschondroplasia (osteochondrosis). Understanding of contri butory, and possibly triggering factors such as this may allow the dev elopment of modified methods of husbandry which minimise the risk of d isease in populations with a known predisposition.