PRODUCTION OF INSULIN-LIKE GROWTH FACTOR-I (IGF-I) BY HUMAN PLACENTAL TISSUE

Abstract

Previous data revealed that a variety of mouse fetal tissues, with the exception of the placenta, are capable of producing IGF-I that may act locally to regulate fetal growth (D'Ercole, et al.,Dev. Biol. 75: 315, 1980). Although the placenta is essential for normal fetal development, little is known regarding the mechanisms controlling placental growth. Human placental explants were examined at various stages of gestation for the ability to produce IGF-I in organ culture. The placental explants were washed extensively and incubated in serum-free media. The media was acidified and chromatographed over a Sephadex G-50 column to separate the IGF-I from specific binding proteins. IGF-I was measured by specific radioimmunoassay (RIA). Placental tissue from all gestational ages secreted immunoreactive IGF-I, 2.19±.35 ng./mg. prot./48 hrs. (Mean±S.D.). There was no difference in IGF-I production between pre-term (9-19wk.) and term placentae under these conditions. The activity was reduced >60% by 50 uM cyclohexamide, suggesting that most of the activity was the result of de novo protein synthesis. The similarity of this material to authentic human IGF-I is supported by parallel displacement in the RIA and co-elution on a Sephadex G-50 column. The human placenta contains specific IGF receptors. These data demonstrate that the human placenta is also capable of producing IGF-I, that may act locally to regulate placental growth.