Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein 3 during the First Year in Term and Preterm Infants

Abstract

Plasma IGF-I and IGF-binding protein 3 (IGFBP-3) were determined by radioimmunoassay in term infants (n = 51) at 0, 2,4, 6, and 12 mo and preterm infants (n = 51) at -3 (28.4 wk postconceptional age), -2, -1.5, -1,0,2,4,6,9, and 12 rna from expected term. The effects of gestational age at birth (term or preterm) and study age were determined by repeated measures analysis of variance and Fisher's least squares difference. In preterm infants, IGF-I increased between -3 and 2 mo from 0.75 to 10.4 nM, decreased between 2 and 9 mo to 7.3 nM, and increased again between 9 and 12 mo to 10.1 nM (p < 0.0001), whereas IGFBP-3 increased relatively little from -3 to 0 rna (14.2 to 30.2 nM, p < 0.05) and plateaued from 2 to 12 mo (49.8 to 62.3 nM). At 0 rna, IGF-I and IGFBP-3 were the same in term and preterm infants, but preterm infants had higher IGF-I from 2 IGF mediate the growth-promoting actions of growth hormone in regulating the proliferation and differentiation of different cell types (1). These polypeptides which are structurally homologous to insulin also exert insulin-like metabolic effects. Both these effects are mediated through target cell surface receptors (2). Most tissues in the body produce IGF, and they are present in serum mostly bound to specific high molecular weight binding proteins (3). Of the six IGFBP that have been identified so far, IGFBP-3 is the major form present in the serum (1, 2) and demonstrates a high affinity for both IGF-I and IGF-II. IGFBP-3 can exhibit either an inhibitory (4) or a potentiating (5) effect on IGF-I bioactivity in vitro, depending on its ability to alter the equilibrium between IGF-I and its receptor (5).

Onset of Significant GH Dependence of Serum IGF-I and IGF-Binding Protein 3 Concentrations in Early Life

“…The marked variations in the serum concentrations of IGF-I in the first 18 mo of life will limit its usefulness in the assessment of growth disorder in early life. Contrary to our study, two previous studies reported little variation in the serum IGF-I concentration in the first 1-2 y of life (10,24). The reasons behind this difference in the reported developmental serum growth factors profile are not immediately apparent.…”

“…Significant correlation between serum IGF-I and IGFBP-3 concentration was demonstrated in infants from birth to 18 mo of age, consistent with findings from previous studies (10,24,30). A significant increase in serum IGFBP-3 concentration with age was noted in our babies, with a significant rise occurring first at 10 mo of age.…”

Physical Growth and Retinopathy in Preterm Infants: Involvement of IGF-I and GH

“…Newborns show a state of GH resistance, characterized by GH hypersecretion and a low serum IGF-I level (11,12). We observed that this unique profile was more prominent in extremely preterm infants and continued for 3 mo after birth.…”

“…GH levels are higher in fetuses and newborns than in children and adults (9). Especially in preterm infants, remarkably high GH and low IGF-I values in serum continue until 1 y of age (10)(11)(12). However, the growth effect of GH does not become apparent until about 18 mo of age, and the clinical significance of GH for perinatal growth has not been well understood (1).…”

The Role of Maternal Factors, Postnatal Nutrition, Weight Gain, and Gender in Regulation of Serum IGF-I among Preterm Infants

“…AGA infants who are born preterm have increasing serum IGF-I and reach the same values at an age corresponding to term as infants born AGA at term (38). Thus, it seems that weight appropriate for age is as important at birth as during the neonatal period for increasing the serum IGF-I to the levels in AGA infants, and that postnatal growth retardation might be as harmful as intrauterine growth retardation.…”