Insulin-like growth factors (IGF) I and II and IGF binding proteins (IGFBPs) in human colostrum/transitory milk during the first week postpartum: comparison with neonatal and maternal serum.

Day 1 human colostrum contains 5 times more IGF I than IGF II. By day 3 postpartum, IGF I drops by 80% to constant levels whereas IGF II increases 3-fold up to day 7. Colostrum contains mainly IGFBP-2, little IGFBP-3 and no detectable IGFBP-1 or IGFBP-4. IGFBP-2 rises 20-fold up to day 6 of lactation. The major IGFBPs of newborn serum are IGFBP-2, -3 and -4. Early maternal serum contains only small amounts of IGFBP-2 and -3 and no detectable IGFBP-4. The pronounced differences between the IGFBP patterns of colostrum and early maternal serum suggest that IGFBP-2 does not pass from maternal blood into colostrum but is produced and secreted by mammary tissue itself. On the other hand, most of the IGF I, but not IGF II, in day 1 colostrum appears to stem from the maternal circulation.