Regulation of gonadal and somatotropic axis by chronic intraventricular infusion of insulin-like growth factor 1 antibody at the initiation of puberty in male rats

There has been increasing experimental evidence to suggest that insulin-lik e growth factor 1 (IGF-I) may be one of the essential regulators in the rep roductive system of the rat. IGF-I is synthesized in the hypothalamus and I GF-I immunoreactivity increases during puberty. Consequently we hypothesize d that centrally located IGF-I might contribute to the initiation of pubert y. Centrally located IGF-I was immunoneutralized to assess this hypothesis. Male Wistar rats, 28 days old, were infused intracerebroventricularly with specific purified IgGs from rabbit IGF-I antiserum (IGF-I-Ab). The intrace rebroventricular administration of IGF-I-Ab resulted in a reduction in test icular weight and consequently in delayed pubertal development. There was a lso a reduction in serum testosterone, pituitary immunoreactive (IR) lutein izing hormone (LH) and serum IR follicle-stimulating hormone (FSH). The acc umulation of beta LH mRNA was not modified, whereas beta FSH mRNA was incre ased. An increment in the serum growth hormone (GH) levels was also observe d. There were no significant alterations in hypothalamic IR growth hormone releasing factor content, although IR somatostatin (SRIH) content was incre ased by IGF-I-Ab. The body weight gain remained unaltered. As a whole, our study suggests that centrally located IGF-I influences pubertal development , production and release of gonadotropins and supports the finding that end ogenous centrally located IGF-I plays a role at the initiation of puberty i n the male rat. It also gives support to the physiological role of centrall y located IGF-I in the release of GH mediated by hypothalamic SRIH at the i nitiation of puberty.