RESUMO
The actions of mammalian insulin-like growth factors (IGF-I and IGF-II) and insulin on skeletal growth of the axolotl, Ambystoma mexicanum, were examined by monitoring the in vitro uptake of [35S]sulfate by cartilage. Both growth factors stimulated sulfate uptake significantly at a concentration of 13 nM. The increase after incubation with 130 nM insulin was similar (uptake ca. 160% of control), but the effect was not significant. Further, the binding of 125I-IGF-I and 125I-IGF-II was studied in the skeletal tissue by quantitative in vitro autoradiography. Specific binding sites for both growth factors were localized in the perichondrial tissue. 125I-IGF-II binding sites were saturated at the used doses. Scatchard and Hill plots demonstrate heterogeneous binding sites exhibiting positive cooperativity. IGF-II was more effective than IGF-I in competitively displacing both labeled ligands. Insulin only slightly affected the binding at the highest concentrations. These results indicate that the insulinlike growth factors regulate skeletal growth in urodeles as in mammals.