Introduction: Insulin like growth factor I and II (IGF I and II) play an important role in the regulation of human fetal growth and development and elicit their biological actions mainly via the IGF-I receptor.

Methods: In order to elucidate IGF-brinding in human fetal tissues and placenta we incubated cryosections of placenta and fetal tissues with [125I]IGF-I in the presence and absence of unlabeled IGF-I and performed in-situ hybridzation with a digoxigenin-labeled cRNA probe for IGF-I receptor. The aim of the study was firstly to provide a detailed assessment of IGF-I binding in human fetal tissues by IGF-I receptor macro- and microautoradiography and secondly to localize IGF-I binding at the cellular level.

Results: Binding of [125I]IGF-I to cryosections of human term placenta and fetal tissues at 15 °C was specific and halfmaximally inhibited by unlabeled IGF-I at 2.1 ± 1.2 × 10-9 M. Unlabeled IGF-II was 15-18-fold, and insulin 900-940-fold respectively, less potent in inhibiting binding of [125I]IGF-I to the two tissues. Findings were in accordance with in-situ hybridization studies for IGF-I-receptor mRNA.

Conclusion: We conclude that both methods serve as an accurate tool in the identification of IGF-I receptors in human fetal tissues and placenta, specific binding of IGF-I can be localized to growtsensitive areas and is in accordance with preliminary studies of IGF expression in the human fetus and placenta. Our results indicate a possible relationship between IGF-binding and fetal growth and development, which may be an important tool for developmental and nutritional status in the future.