Free IGF-I, IGFBP-1, and the binary complex of IGFBP-1 and IGF-I are increased during human pregnancy.
OBJECTIVE
To investigate changes in free insulin-like growth factor I (IGF-I) and IGF-binding protein 1 (IGFBP-1) complexed IGF-I during human pregnancy.


METHODS
Overnight fasting serum was obtained in a longitudinal design from 11 women with non-complicated pregnancy at gestation weeks 6-10, 16-20, 24-28 and 35-38 and, for comparison, 5 weeks post-partum. All samples were analyzed for total and free IGF-I and IGF-II, IGFBP-3 and IGFBP-3 proteolysis, total and non-phosphorylated (np-) IGFBP-1, and IGFBP-1 complexed IGF-I.


RESULTS
Total IGF-I was increased in late pregnancy (week 35-38) (p < 0.001), whereas free IGF-I was significantly increased by 77% already at week 6-10 (p = 0.004) and by 140% (p = 0.002) at week 34-38, when compared to post-partum levels. At weeks 16-20 and 24-28, levels of free IGF-I were not significantly different from post-partum levels. Significant IGFBP-3 proteolysis was detectable from week 6-10 and throughout pregnancy (p < 0.05). Total and np-IGFBP-1 were significantly increased from 16-20 weeks of pregnancy (both p < 0.05) and IGFBP-1 complexed IGF-I was increased 2-fold from week 16-20 and throughout pregnancy (p < 0.05). However, the saturation of IGFBP-1 remained constant at 27-29% during the study.


CONCLUSIONS
We found evidence of increased free IGF-I and increased IGF-I in binary complexes during pregnancy, possibly caused by IGFBP-3 proteolysis and decreased ternary complex formation.
Skjaerbaek
Christian
C
Medical Research Laboratories, Institute of Experimental Clinical Research, Aarhus University Hospital, Aarhus, Denmark. csk@dadlnet.dk
Frystyk
Jan
J
Orskov
Hans
H
Flyvbjerg
Allan
A
D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood* / Q000737:chemistry; D007334:Insulin-Like Growth Factor I / Q000737:chemistry / Q000378:metabolism*; D046912:Multiprotein Complexes; D011247:Pregnancy / Q000097:blood*; D011257:Pregnancy Proteins / Q000097:blood* / Q000737:chemistry; D013997:Time Factors
C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D018969:Insulin-Like Growth Factor Binding Proteins; D046912:Multiprotein Complexes; D011257:Pregnancy Proteins; D007334:Insulin-Like Growth Factor I