The main circulating insulin-like growth factor-binding protein (IGFBP) in human, IGFBP-3, markedly decreases during pregnancy, as determined by Western ligand blotting, and its decrease is due to an endogenous pregnancy-related serum IGFBP-3 proteolytic activity. Proteolysis of IGFBP-3 may result in the free form of IGF-I (fIGF-I) being liberated from or weakly bound to IGFBP-3 fragments. The purpose of this study was to determine the plasma concentration of fIGF-I and the mechanism of fIGF-I regulation during normal human pregnancy. We studied 19 normal pregnant women at 6–8 weeks gestation, 24 normal pregnant women at 28–30 weeks gestation, and 25 nonpregnant women. We measured plasma fIGF-I using a recently established immunoradiometric assay. We also measured plasma total IGF-I (free plus complexed forms of IGF-I) using immunoradiometric assay, and IGFBP-3 proteolytic activity using a IGFBP-3 protease assay. fIGF-I levels at 6–8 weeks gestation (4.11 ± 0.23 ng/mL) and at 28-30 weeks gestation (3.67 ± 0.21 ng/mL) were significantly higher than that in nonpregnant women (2.48 ± 0.12 ng/mL; P < 0.001 in both). Total IGF-I levels at 6–8 weeks gestation (168.0 ± 9.1 ng/mL) and at 28–30 weeks gestation (241.5 ± 19.0 ng/mL) were significantly lower than that in nonpregnant women (283.9 ± 12.3 ng/mL; P < 0.001 at 6–8 weeks gestation and P < 0.05 at 28–30 weeks gestation). All pregnant serum studied had IGFBP-3 proteolytic activity. These data indicate that during normal human pregnancy, circulatory fIGF-I increases, probably due to IGFBP-3 proteolytic activity.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical