Developmental regulation of placental insulin-like growth factor (IGF)-II and IGF-binding protein-1 and-2 messenger RNA expression during primate pregnancy

The present study was conducted to determine the developmental expression o f placental insulin-like growth factor (IGF)-II, IGF-binding protein (IGFBP )-1 and -2, and IGF-II receptor mRNA expression during baboon pregnancy and whether estrogen, the levels of which increase with advancing pregnancy, r egulates placental trophoblast IGF-II mRNA expression. Levels of the IGF-II 6.1-kilobase (kb) and 4.9-kb mRNA transcripts determined by Northern blot analysis progressively increased three-to fourfold in placental syncytiotro phoblast and whole-villous tissue between early (Day 60), mid (Day 100), an d late (Day 170) baboon gestation (term = 184 days). In contrast, syncytiot rophoblast IGFBP-1 and -2 mRNA levels decreased, and IGF-II receptor mRNA e xpression remained relatively constant, with advancing baboon pregnancy. Pl acental cytotrophoblast IGF-II mRNA levels determined by competitive revers e transcription-polymerase chain reaction on Day 54 of gestation were incre ased (P < 0.05) almost twofold at 18 h after acute administration of estrad iol to baboons, whereas long-term estrogen treatment had no effect. We prop ose that these changes in trophoblast IGF expression would provide a mechan ism for enhancing net bioavailability and bioreactivity of IGF-II locally t o promote the growth and development of the placenta and, consequently, of the fetus during primate pregnancy.