Interactions between steroid hormones and insulin-like growth factor-I in rabbit chondrocytes

The mechanism of action of steroid hormones on skeletal growth is not understood in detail. We examined the interactions of steroid hormones and insulin-like growth factor-I (IGF-I) during DNA and sulfated proteoglycan synthesis in rabbit costal chondrocytes. Progesterone at 0.05 nM stimulated the incorporation of [3H]thymidine into DNA by 30% above the control level in confluent cultures, but neither testosterone nor 17 beta-estradiol stimulated DNA synthesis. None of the hormones affected [3H]thymidine incorporation stimulated by IGF-I when chondrocytes were incubated with one of the hormones and IGF-I simultaneously. In contrast, when confluent cultures were incubated with one of the sex steroids for 24 h before the addition of IGF-I, stimulation of DNA synthesis by the growth factor was enhanced about 45% above the control value by 0.5 nM progesterone, 50% by 0.5 nM testosterone, and 80% by 50 nM 17 beta-estradiol. The effects of IGF-I on proteoglycan synthesis, as judged by the incorporation of [35S]sulfate, were stimulated by treatment with progesterone or testosterone. Dexamethasone at physiological concentrations inhibited chondrocyte DNA synthesis in confluent cultures to 10% of the control level. At 50 nM, dexamethasone suppressed IGF-I induction of DNA synthesis by 60%. This suppression was greater when dexamethasone was added before IGF-I than when the additions were simultaneous. When chondrocytes were treated with hydrocortisone or dexamethasone for 24 h before the addition of IGF-I, the glucocorticoids synergistically accelerated proteoglycan synthesis mediated by IGF-I. These findings suggest that steroid hormones have priming effects on the biological action of IGF-I in cartilage metabolism.