Effects of glucocorticoids on cartilage growth and response to IGF-I in the Tilapia (Oreochromis mossambicus)

To study the effects of glucocorticoids and IGF-I on the modulation of grow th in the tilapia Oreochromis mossambicus, we employed an epiceratobranchia l cartilage radioisotope incorporation assay, wherein radiolabeled sulfate and thymidine uptakes are measured in vitro to indicate proteoglycan synthe sis and cell proliferation, respectively. Cartilage explants were cultured with cortisol or dexamethasone with or without recombinant bovine insulin-l ike growth factor-I. Cortisol directly inhibited sulfate uptake at 100 and 1000 ng/mL concentrations in a concentration-dependent manner but inhibited thymidine uptake significantly only at the 1000 ng/mL concentration. Dexam ethasone inhibited sulfate and thymidine uptake at concentrations similar t o the effective concentrations of cortisol. Cortisol did not inhibit IGF-I stimulation of sulfate uptake at any of the concentrations tested. Furtherm ore, cortisol did not inhibit thymidine uptake when IGF-I was present in th e medium. Cortisol appears to act directly on cartilage and not by interact ing with the IGF-I system. However, the physiologically significant role of cortisol is mainly an inhibitory one on cartilage metabolism. The data gen erally indicate an inhibitory role for glucocorticoids on cartilage growth but an inability to counter the stimulation of sulfate uptake by IGF-I. (C) 2001 Academic Press.