Insulin-like growth factor-I (IGF-I) and IGF-binding proteins both decline in the rat during late pregnancy

J Endocrinol. 1990 Dec;127(3):383-90. doi: 10.1677/joe.0.1270383.

Abstract

Insulin-like growth factor-I (IGF-I), IGF-II and IGF-binding proteins (IGFBP) were examined in rat serum during pregnancy and lactation. IGF-I concentrations determined after acid column chromatography of serum were low during the last third of pregnancy. IGF-II was undetectable in pregnant and non-pregnant rats. IGF-binding protein (IGFBP) concentrations, measured as high molecular mass activity in the IGF-I RIA and the IGF-II RRA of acid column fractions, paralleled the changes observed with IGF-I. Western ligand blot analysis of serum from non-pregnant rats revealed a 40-50 kDa IGFBP aligning with IGFBP-3, a smaller 28-30 kDa doublet and 24 kDa IGFBP. Serum from rats in late pregnancy lacked IGFBP-3, whereas the smaller IGFBP persisted during late pregnancy. IGFBP-3 reappeared in postpartum animals. The fall in serum IGF-I is consistent with a maternal catabolic state during late pregnancy which may maximize substrate availability for the developing fetus.

MeSH terms

  • Animals
  • Blotting, Western
  • Carrier Proteins / blood*
  • Chromatography
  • Female
  • Insulin-Like Growth Factor Binding Proteins
  • Insulin-Like Growth Factor I / metabolism*
  • Lactation / blood
  • Pregnancy
  • Pregnancy, Animal / blood*
  • Radioimmunoassay
  • Radioligand Assay
  • Rats
  • Rats, Inbred Strains
  • Somatomedins / metabolism*

Substances

  • Carrier Proteins
  • Insulin-Like Growth Factor Binding Proteins
  • Somatomedins
  • Insulin-Like Growth Factor I