Effect of insulin-like growth factor (IGF)-1 and R3 IGF-1 (an analog of IGF-1 with a greatly reduced affinity for IGF-binding proteins) on total proteoglycan synthesis by human osteoarthritis chondrocytes. Cells were stimulated for 48 hours with 2.7 nM IGF-1 or R3 IGF-1 and total proteoglycan synthesis was measured. Data are expressed as the means and SEM of four replicates from a representative experiment (out of three independent cultures). Statistical differences from the control were measured using Student's t-test. ***P < 0.001.