INSULIN-LIKE GROWTH-FACTORS (IGFS), IGF-BINDING PROTEINS (IGFBPS), AND PROTEOLYZED IGFBP-3 IN EMBRYONIC CAVITIES IN EARLY HUMAN-PREGNANCY -THEIR POTENTIAL RELEVANCE TO MATERNAL-EMBRYONIC AND FETAL INTERACTIONS

insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are believed to be important in fetal growth and development. In the current study, the developmental changes in the IGF and IGFBP axis wer e examined in 23 paired samples of human amniotic fluid (AF), extraemb ryonic coelomic (EEC) fluid, and maternal serum (MS) between 9 and 12 weeks gestation. Levels of IGF-I were very low in AF (7 +/- 3 ng/mL) a nd EEC (10 +/- 3 ng/mL) compared to those in MS (237 +/- 42 ng/mL). In contrast, IGF-II concentrations were 210 +/- 36 and 174 +/- 22 ng/mL in AF and EEC, respectively, and were approximately 25% of MS serum le vels (884 +/- 122 ng/mL). There was no dependence on gestational age f or either peptide in AF or EEC during the period of gestation examined . IGFBP-1 levels in AF increased about 20-fold (1.6 +/- 0.3 to 33.0 +/ - 0.1 ng/mL) between 9 and 12 weeks of pregnancy, and IGFBP-1 levels w ere nearly 2 orders of magnitude higher in EEC, increasing about 100-f old (365 +/- 119 to 3014 +/- 100.0 ng/mL) by the end of the first trim ester. In contrast, IGFBP-1 levels were low in MS (24.9 +/- 3.5 ng/mL) and showed no gestational age dependence. Using RIA, high levels of I GFBP-3 were found in EEC (2062 +/- 177 ng/mL) and MS (6590 +/- 357 ng/ mL) compared to those in AF (152 +/- 24 ng/mL). Levels of IGFBP-3 in M S and EEC did not change significantly with gestational age, whereas a n increase in IGFBP-1 was observed in AF after the tenth week of pregn ancy. In contrast to high levels of IGFBP-3 in MS and EEC, determined by RIA, the 37- to 43-kilodalton IGFBP-3 doublet was barely detectable by Western ligand blot analysis. This discrepancy suggested the prese nce of an IGFBP-3 protease in EEC, as has been found in MS, that decre ases the affinity of this BP for IGF peptides and, therefore, renders it less readily detectable by Western ligand blot analysis. Using [I-1 25]IGFBP-3 as substrate, lower levels of IGFBP-8 protease activity wer e detected in EEC compared to MS, and nearly undetectable levels were found in AF. By Western immunoblotting, a smaller (28-kilodalton) immu noreactive form of IGFBP-3 was detected only in MS and EEC, suggesting proteolyzed IGFBP-3 in MS and EEC, but not in AF, during this gestati onal period. These data show that IGF-II is the predominant IGF in ext raembryonic cavities of the developing human embryo/fetus. In addition , the high levels of IGFBP-3 and IGFBP-1 present in EEC compared to AF suggest that the amnion serves as an effective barrier for transport of the higher mol wt IGFBPs from EEC to AF. Although the sites of synt hesis of IGF-II, the IGFBPs, and IGFBP-3 protease are uncertain, the m aternal decidua and chorion laeve are likely sources. As the chorionic cavity (EEC) is compressed by the expanding amnion as the first trime ster proceeds, and the chorion itself comes into contact with the mate rnal decidua parietalis at the end of this period, it is likely that c omponents from the maternal decidua are transported into the EEC befor e 12 weeks gestation, and then directly into AF thereafter. Synthesis of some of the components of the IGF system by the extraembryonic memb ranes is also possible. We propose that the relative affinities of par tially proteolyzed IGFBP-3 and IGFBP-1 for IGF-II in EEC regulate the amount of bioavailable IGF-II for action on target cells within the ch orion and/or amnion. The presence of IGFs, IGFBPs, and lower mol wt fo rms of IGFBP-3 in human extraembryonic cavities that may be both mater nally and fetally derived suggests that crosstalk between the maternal host and the early developing embryo/fetus is an important process in early fetal development.