Growth hormone bioactivity and levels of growth hormone, growth hormone-binding protein, insulinlike growth factor I, and insulinlike growth factor-binding proteins in premature and full-term newborns during the first month of life

Objective: To assess the pattern of growth hormone bioactivity (GH-BIO) and the levels of GH-binding protein (GH-BP), insulin-like growth factor I (IGF-I), and insulin-like growth factor-binding proteins (IGFBPs) in the first month of life in premature and full-term (FT) newborns. Patients and Methods: Serum samples were collected from 9 premature newborns who were small for gestational age, 18 premature newborns who were of appropriate size for gestational age, and 20 FT newborns on the 4th and 30th days of life to evaluate the GH-BIO using the Nb2 cell bioassay, the GH levels using a radioimmunoassay (GH-RIA), and the levels of GH-BP, IGF-I, and IGFBPs. Results: On day 4, the GH-RIA and GH-BIO values were increased in all newborns (P lt .05) compared with values in the prepubertal control subjects. The GH-BP levels were low in all newborns, with the lowest values (P lt .05) found in the premature newborns and positively correlated with gestation age (P lt .001). The IGF-I levels were also low, with lower values (than those found in the FT newborns) (P lt .005) found in the premature group and positively correlated with the GH-BP levels (P lt .001) and gestational age (P lt .001). The levels of IGFBP-1 and IGFBP-2 were high, with higher values found in the premature newborns than in the FT newborns (P lt .05) and negatively correlated with gestational age (P lt .005). The IGFBP-3 level was lower in the premature (P lt .05) than in the FT newborns and positively correlated with gestational age (P lt .005). During the first month of life, the GH-RIA and GH-BIO values were significantly decreased in all newborns (P lt .001), while the IGF-I level was increased in the premature newborns (P lt .005). The GH-BP levels were increased only in the FT newborns (P lt .001). Conclusions: The elevated bioactive GH level seen in the first few days of life seemed to be attributable to a low IGF-I level secondary to a decreased number and/or function of the GH receptors. The decrease in the serum GH level observed thereafter seemed to be secondary to an increase in the IGF-I level in the premature newborns; however, other factors may have been involved in the FT newborns in whom no increase in the IGF-I level was observed.