F. Pazos et al., Mechanisms of reduced body growth in the pubertal feminized male rat: Unbalanced estrogen and androgen action on the somatotropic axis, PEDIAT RES, 48(1), 2000, pp. 96-103
It is well known that the sex difference in body growth at puberty is modul
ated by a complex interplay between sex steroids and somatotropic axis; how
ever, the exact role played by sex steroids remains a matter of controversy
. The aim of this study was to assess the mechanisms by which sex steroids
regulate body growth during pubertal development. Flutamide, a non-steroid-
blocking androgen receptor, was subcutaneously administered to 30-d-old mal
e Wistar rats for 4 wk. The blockade of the androgen receptor led to a mark
ed elevation in serum testosterone and an increment in serum estradiol. Flu
tamide administration decreased body weight gain, serum IGF-I levels, hepat
ic IGF-I mRNA, and GH receptor mRNA content. There were no significant chan
ges in serum GH concentration, pituitary GH reserve, and pituitary GH mRNA
content. Flutamide lowered hypothalamic somatostatin mRNA content and augme
nted hypothalamic immunoreactive somatostatin stores, but did not alter hyp
othalamic immunoreactive GH-releasing factor stores. Our findings indicate
that during pubertal development of the male rat, the imbalance between and
rogen and estrogen actions determines an abnormal somatic growth, which is
at least partly exerted through the peripheral or hepatic modification of t
he somatotropic axis that occurs under the high or exclusive action of estr
ogens. Potential implication of coincident sex-specific regulated mode of p
ulsatile GH secretion cannot be excluded from this random serum GPI sample
study.