GROWTH-HORMONE BIOACTIVITY AND LEVELS OF GROWTH-HORMONE, GROWTH HORMONE-BINDING PROTEIN, INSULIN-LIKE GROWTH-FACTOR-I, AND INSULIN-LIKE GROWTH FACTOR-BINDING PROTEINS IN PREMATURE AND FULL-TERM NEWBORNS DURINGTHE FIRST MONTH OF LIFE

Objective: To assess the pattern of growth hormone bioactivity (GH-BIO ) and the levels of GH-binding protein (GH-BP), insulinlike growth fac tor I (IGF-I), and insulinlike 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 ne wborns who were small for gestational age, 18 premature newborns who w ere 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 b ioassay, the GH levels using a radio-immunoassay (GH-RTA), and the lev els of GH-BP, IGF-I, and IGFBPs. Results: On day 4, the GH-RIA and GH- BIO values were increased in all newborns (P<.05) compared with values in the prepubertal control subjects. The GH-BP levels were low in all newborns, with the lowest values (P<.05) found in the premature newbo rns and positively correlated with gestational age (P<.001). The IGF-I levels were also low, with lower values (than those found in the FT n ewborns) (P<.005) found in the premature group and positively correlat ed with the GH-BP levels (P<.001) and gestational age (P<.001). The le vels of IGFBP-1 and IGFBP-2 were high, with higher values found in the premature newborns than in the FT newborns (P<.05) and negatively cor related with gestational age (P<.005). The IGFBP-3 level was lower in the premature (P<.05) than in the FT newborns and positively correlate d with gestational age (P<.005). During the first month of life, the G H-RIA and GH-BIO values were significantly decreased in all newborns ( P<.001),while the IGF-I level was increased in the premature newborns (P<.005). The GPI-BP levels were increased only in the FT newborns (P< .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 second ary to a decreased number and/or function of the GH receptors. The dec rease in the serum GH level observed thereafter seemed to be secondary to an increase in the IGF-I lever in the premature newborns; however, other factors may have been involved in the FT newborns in whom no in crease in the IGF-I level was observed.