Effects of antiandrogens and ethane dimethane sulphonate (EDS) on gene expression, free subunits, bioactivity and secretion of pituitary gonadotrophins in male rats

Abstract

In the male rat, testosterone has been shown to regulate gonadotrophin synthesis and secretion under experimental conditions such as castration or gonadotrophin-releasing hormone (GnRH) antagonist with or without testosterone. The present study aims at clarifying the effects of non-steroidal antiandrogens, Casodex and flutamide, and ethane dimethane sulphonate (EDS) on the regulation of gonadotrophin synthesis and secretion. To enable a direct comparison within this study to expected effects of testosterone, a GnRH antagonist-treated group and a castrated group were included. The gene expression of the subunits was correlated with changes in the pituitary and plasma content of immunoreactive luteinizing hormone (LH) and follicle-stimulating hormone (FSH), free subunits and pituitary content of in vitro bioactive LH and FSH. Groups of ten male rats each received the following treatments for 7 days: (1) vehicle; (2) castration; (3) EDS (75 mg/kg); (4) GnRH antagonist (Cetrorelix 250 μg/kg/day), (5) Casodex (20 mg/kg/day) or (6) flutamide (20 mg/kg/day). The effectiveness of testosterone deprivation was demonstrated by the reduction of weight in androgen-dependent organs such as epididymides and seminal vesicles in the treated groups. Treatment with flutamide, EDS or castration significantly increased ( p < 0.05) serum levels of LH, FSH and α-subunit, whereas serum gonadotrophin levels were decreased in the GnRH antagonist-treated group. α-Subunit mRNA levels were elevated in the castrated, EDS and flutamide group and LH-β mRNA levels were increased in the castrated and EDS group. FSH-β mRNA levels were increased in the castrated group and decreased in the GnRH antagonist group, but remained unchanged in the flutamide and EDS group. In the flutamide and EDS group an overall decrease of pituitary content of free FSH-β subunit, immunoreactive FSH and bioactive FSH was observed after 7 days of treatment. This effect was not seen for LH. Casodex neither changed mRNA levels nor serum levels of the gonadotrophins, although the pituitary content of free LH-β subunit and bioactive LH and, in addition, testosterone serum levels were elevated. In summary: (1) Selective testosterone blockade/deprivation induced by flutamide and EDS uncoupled the gene expression of FSH-β subunit and secretion of FSH in vivo; (2) antiandrogens and EDS did not affect FSH-β mRNA levels; (3) in the EDS- and flutamide-treated group pituitary free FSH-β, immunoreactive and bioactive FSH were depleted; (4) Casodex seems to have a specific effect on pituitary LH bioactivity and free LH-β subunit, without altering FSH. These findings might indicate that testosterone exerts divergent effects at the pituitary level, namely increasing FSH-β mRNA availability and decreasing pituitary responsiveness to GnRH, thereby lowering FSH secretion. Furthermore, a steady-state level of FSH-β mRNA is maintained by GnRH and testicular factors other than testosterone. Treatment with antiandrogens might provide a useful tool to study the regulation of synthesis and secretion of FSH in vivo.