title: Postnatal variations of growth hormone bioactivity and of growth hormone-dependent factors.
abstract: OBJECTIVE
  To evaluate whether the low insulinlike growth factor I (IGF-I) levels that are observed in the neonate depend on the biological inactivity of the molecular forms of growth hormone (GH) or on the immaturity of the hepatic GH receptors during the early postnatal period.
  
  
  METHODS
  Serum samples were collected from 60 normal full-term neonates on day 5 and at 1 and 4 months of age to evaluate the GH concentrations by using both an immunofluorometric assay and Nb2 cell bioassay, as well as the GH-binding protein, IGF-I, and IGF-binding protein 3 values by radioimmunoassay.
  
  
  RESULTS
  Five-day-old neonates showed significantly higher (P < .001) mean +/- SEM GH levels that were measured by using the immunofluorometric assay (27.22 +/- 1.62 micrograms/L) and Nb2 cell bioassay (3.56 +/- 0.14 U/mL) compared with those levels in 11 prepubertal children who were studied as control subjects (1.26 +/- 0.28 micrograms/L and 0.74 +/- 0.08 U/mL, respectively). At 1 and 4 months of age, GH values that were measured by using both the immunofluorometric assay (9.15 +/- 0.89 and 2.58 +/- 0.32 micrograms/L, respectively) and Nb2 cell bioassay (2.52 +/- 0.11 and 1.71 +/- 0.15 U/mL, respectively) were decreased significantly (P < .001). In 5-day-old neonates, we observed significantly lower (P < .001) serum GH-binding protein (9.73% +/- 0.42%), IGF-I (67.63 +/- 5.20 ng/mL), and IGF-binding protein 3 (1.46 +/- 0.17 mg/L) concentrations compared with those in the prepubertal children (30.74% +/- 2.01%, 210 +/- 25 ng/mL, and 3.08 +/- 0.22 mg/L, respectively). At 1 month of age, serum GH-binding protein (16.00% +/- 0.70%) and IGF-binding protein 3 (2.96 +/- 0.30 mg/L) values were increased significantly (P < .001), while IGF-I levels (72.55 +/- 7.6 ng/mL, P = .09) were not increased. Serum IGF-I values were increased significantly (P < .005) at 4 months of age (97.94 +/- 9.68 ng/mL).
  
  
  CONCLUSIONS
  The interaction of bioactive molecular forms of GH with the increased hepatic GH receptors induces the rise in postnatal IGF-I levels in early infancy.
authors.affiliation: Department of Pediatrics, University of Pavia, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Bozzola
authors.forename: K
authors.initials: K
authors.lastname: Tettoni
authors.forename: F
authors.initials: F
authors.lastname: Locatelli
authors.forename: G
authors.initials: G
authors.lastname: Radetti
authors.forename: C
authors.initials: C
authors.lastname: Belloni
authors.forename: M
authors.initials: M
authors.lastname: Autelli
authors.forename: M
authors.initials: M
authors.lastname: Zecca
authors.forename: R
authors.initials: R
authors.lastname: Valentini
authors.forename: F
authors.initials: F
authors.lastname: Severi
authors.forename: L
authors.initials: L
authors.lastname: Tatò
mesh_terms: D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005314:Embryonic and Fetal Development / Q000502:physiology; D005260:Female; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn / Q000097:blood*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood*; D008099:Liver / Q000502:physiology; D008297:Male; D011863:Radioimmunoassay; D011986:Receptors, Somatotropin / Q000502:physiology
chemical_list: D018969:Insulin-Like Growth Factor Binding Proteins; D011986:Receptors, Somatotropin; D019382:Human Growth Hormone