Mechanisms of reduced body growth in the pubertal feminized male rat: Unbalanced estrogen and androgen action on the somatotropic axis

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.