Inhibitory effects of long-term repeated treatments of a sustainable GnRH antagonist, degarelix acetate, on caprine testicular functions

Abstract

We investigated the effects of long-term repeated treatments with a sustainable gonadotropin-releasing hormone (GnRH) antagonist, degarelix acetate, on testicular hormonal secretion, size, ultrasound images, histology and spermatogenesis in goats to assess its efficacy as a chemical castration method. Male Shiba goats (3-6 months of age) were treated subcutaneously with degarelix acetate every 4 weeks for 24 weeks. Plasma testosterone and insulin-like peptide 3 concentrations decreased (P < 0.05) within 2 days after the first treatment and remained low until 29 weeks (P < 0.05). Scrotal circumference and testicular pixel intensity were lower from 2-6 months and from 1-6 months, respectively, compared to the pretreatment values (P < 0.05). The testis and epididymis weights were lower at 24 weeks compared to those in untreated goats (P < 0.05). There were no sperm in the seminiferous tubules of testicular tissue sections or in homogenates of the epididymis at 24 weeks. These results suggest that repeated treatment with degarelix acetate is an effective chemical castration method for goats.

Keywords: Chemical castration; Male goat; Sperm; Sustainable GnRH antagonist; Testicular hormones.

Fig. 1.

Plasma testosterone (A) and insulin-like peptide 3 (INSL3) (B) concentrations in goats treated with a sustained gonadotropin-releasing hormone (GnRH) antagonist (4 mg/kg; subcutaneously). Data are expressed as mean ± SEM (n = 4). Asterisks indicate significant differences (P < 0.05) compared to the pretreatment (day 0). The arrow shows the days of GnRH antagonist treatment.

Fig. 2.

Scrotal circumference (A) and testicular pixel intensity (B) in goats treated with a sustained gonadotropin-releasing hormone (GnRH) antagonist (4 mg/kg; subcutaneously) or without treatments (control). Control animals are non-treated males at corresponding age to the GnRH antagonist-treated males. Data are expressed as mean ± SEM (n = 4). The different letters represent significantly different results (a, b, c, d, e; P < 0.05). The asterisks indicate significant differences compared with the control group (* P < 0.05).

Fig. 3.

Representative testicular histology stained with hematoxylin and eosin in goats treated with a sustained gonadotropin-releasing hormone (GnRH) antagonist (B, D) or without treatments (control) (A, C). Control animals are non-treated males at corresponding age to the GnRH antagonist-treated males. a, Sertoli cells; b, spermatozoa; c, spermatid; d, Leydig cells.

Fig. 4.

Diagrams of experimental designs. (A) The black arrows show days of gonadotropin-releasing hormone (GnRH) antagonist treatment. The open arrow indicates day of orchiectomy. (B) The black triangles show days of blood collection, and white triangles indicate days of scrotal circumference measurements and testicular ultrasonography.