Sex-dependent endocrine and cellular effects of the GnRH antagonist degarelix in rabbits and cell models

Degarelix is a long-acting gonadotropin-releasing hormone (GnRH) antagonist that suppresses gonadotropin and sex steroid secretion via competitive blockade of the GnRH receptor (GnRHR). Although its systemic endocrine effects have been clearly identified, its direct effects on non-pituitary-derived cells, as well as the roles of sex and context-dependent pharmacological properties, remain largely unexplored.

Degarelix was profiled in vitro (HEK293T, CHO-K1 cells) and in vivo (male and female New Zealand rabbits). Cell viability was measured using a cell counting kit-8 (CCK-8) assay. Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E₂, in females), and testosterone (T, in males) were quantified by enzyme-linked immunosorbent assay (ELISA). Transcript levels were assessed by quantitative polymerase chain reaction (qPCR), and GnRHR protein abundance and localization were evaluated in hypothalamic-pituitary-gonadal (HPG) tissues using Western blot and immunohistochemistry (IHC).

In vitro, degarelix exerted direct, time-dependent, and concentration-dependent effects on the viability of non-pituitary-derived cells (P < 0.05), with differential responses observed between HEK293T and CHO-K1 cell lines. In vivo, degarelix induced a biphasic, sex-dependent endocrine response, characterized by a transient elevation (days 1-7) followed by sustained suppression (days 10-28) of gonadotropins and sex steroids, without affecting body weight (P > 0.05). qPCR revealed tissue- and sex-specific transcriptional changes, including upregulation of pituitary follicle-stimulating hormone beta subunit (FSHβ) mRNA in male rabbits and downregulation of hypothalamic GnRHR mRNA in female rabbits. Notably, Western blot and IHC analyses indicated that these mRNA alterations were not accompanied by significant changes in GnRHR protein abundance or localization.

This study systematically demonstrates that degarelix exhibits concentration-dependent, sexually dimorphic, and tissue-specific effects in the regulation of reproductive endocrine functions, as well as direct actions on non-pituitary cells. Furthermore, its direct regulation of non-pituitary cells does not depend on changes in GnRHR protein abundance. These findings provide insight into the mechanisms underlying the antagonistic effects of GnRH and lay a theoretical foundation for the personalized application of degarelix in both experimental and clinical settings.