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
G. Radetti, M. Bozzola, C. Paganini, R. Valentini, L. Gentili, K. Tettoni and L. Tato
Department of Paediatrics, Regional Hospital, Bolzano, Italy.
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 radio-immunoassay (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 < .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 newborns and positively correlated with
gestational age (P < .001). The IGF-I levels were also low, with lower
values (than those found in the FT newborns) (P < .005) found in the
premature group and positively correlated with the GH-BP levels (P <
.001) and gestational age (P < .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 < .05) and negatively correlated with gestational age (P
< .005). The IGFBP-3 level was lower in the premature (P < .05) than
in the FT newborns and positively correlated with gestational age (P <
.005). During the first month of life, the GH-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 GH-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 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.
