OBJECTIVE: To investigate the effects of 17beta-estradiol (E(2)) and progesterone (P) on the expression of IRS in human osteoblast cells (HOBs) and further study the mechanism of E(2) and P on postmenopausal osteoporosis (PMOP). METHODS: Osteoblasts from cancellous bones of normal adults were cultured and underwent intervention of E(2) and P respectively. Semi-quantitative RT-PCR was used to measure the expression of mRNAs of IRS-1 and IRS-2. The expression of the proteins of IRS-1 and IRS-2 were detected by Western blotting. The expressions of phosphorylated IRS protein (P-IRS) was examined by immunocoprecipitation/Western blotting. RESULTS: The expression level of IRS-2 mRNA in the HOBs undergoing intervention of E(2) and P were 421% +/- 68% and 327% +/- 54% that of the control group respectively (P < 0.05 and P < 0.01). The expression level of IRS-2 mRNA in the HOBs undergoing intervention of E(2) combined with P was 496% +/- 54% that of the control group (P < 0.01). However, the expression level of IRS-1 was not significantly influenced by E(2) and/or P (all P > 0.05). The expression level of IRS-2 protein and phophorylated IRS-2 protein in the HOBs undergoing intervention of E(2), P, and E(2) combined with P were 487% +/- 65%, 507% +/- 54%, 552% +/- 47% and 483% +/- 52%, 527% +/- 76%, and 717% +/- 86% that of the control group (P < 0.05, P < 0.01, and P < 0.05). The P-IRS-1 protein level of the HOBs undergoing intervention of E(2), P, and E(2) combined with P were 54% +/- 7.6%, 37% +/- 4.2%, and 21.2% +/- 3.0% that of the control group (P < 0.05, P < 0.01, and P < 0.01). CONCLUSION: E(2) and P up-regulate the expression of IRS-2 mRNA in HOBs. Combined intervention of E(2) and P positively creates a synergistic effect on the up-regulation of IRS-2 mRNA. E(2) and P have no effects on the expression of IRS-1 mRNA. E(2) and P increase the expression of IRS-2 protein and P-IRS-2. Combined intervention of E(2) and P presents a positive synergistic effect on the up-regulation of P-IRS-2. However, they show no effect on the expression of IRS-1 protein, and down regulate the phosphorylation of IRS-1 protein.