INFLUENCE OF SEX STEROIDS ON DEVELOPMENT OF CULTURED FETAL-RAT METATARSAL BONES

The effects of 17 beta-estradiol (E), dihydrotestosterone (D, a non ar omatisable androgen), and progesterone (P) on osteogenesis were studie d on fetal rat cartilaginous anlagues cultivated in vitro. The three m edial metatarsal rudiments were harvested at day 19 of gestation and g rown in 1% BSA MEM medium (MO 643, Sigma) without serum nor antibiotic s. After a 18h preincubation period, hormones were added for 8 days. P aired controls were incubated in the same volume of medium. The length , the metacarpal thickness and the size of the mineralized zone were m easured every day, using a calibrated eyepiece (magnification X 40). D NA and protein synthesis, cartilage metabolism and mineralization were evaluated by monitoring the incorporation of H-3-Thymidine, H-3-Proli ne, S-35 and Ca-45 into anlagues for the last three hours of incubatio n, respectively. The dose/response effect of each steroid was studied at the concentrations of 10(-4) M, 10(-6) M, 10(-7) M and 10(-9) M. No difference was observed between male and female fetuses. A significan t positive effect on total length (% of length measured at harvesting day) was observed with the 10(-7) M dose of E (163% +/- 2 vs 148% +/- 4 in controls) or D (158% +/- 3). Endochondral growth was not modified by P treatment. The effect of the three steroids (given at a dose of 10(-7) M) alone or as combinations (E, D, P, EP, ED, PD, EPD) confirme d the positive effect off on endochondral growth and, to a lesser exte nd, of D and the association ED. Nevertheless, D had a better effect t han E on endomembranous growth. On the contrary, P did not affect grow th neither administrated alone nor in combination with E or D, while a positive effect of P on mineralization was demonstrated. The treatmen t associating the three steroids slowed down all the parameters concer ning growth but strongly stimulated calcification.