Age-related Changes in GnRH-stimulated Peripheral Hormone Levels and Testicular Characteristics of the West African Dwarf Buck

Abstract

The testis in male domestic animals is charged with two primary functions: spermatogenesis and steroidogenesis. These functions are accomplished through a coordinated interaction of the testicular cells under the control of GnRH. The buck, like many male domestic animals, exhibits variations in concentrations of circulating hormones as a function of age, vis-a-vis their testicular mass or diameter and the number of testicular cells. However, it is unclear how age-related peripheral endocrine regulation of testicular size affected the endocrine control of testicular function in the West African dwarf buck. This study therefore examined the testicular features of the West African dwarf buck to ascertain the effects of peripheral and GnRH-stimulated levels of FSH, LH, T, and estradiol from 3 to 12 months of age. In order to achieve this objective, twelve 3-month-old bucks were obtained and randomly allocated into two groups: the GnRH-treated group (n = 6) and the control group (n = 6). Every month, the bucks were weighed, the testicular diameter was measured, and two blood samples were taken from the bucks (n = 12) at a 1-hour interval to establish peripheral concentrations. On the following day, bucks in the GnRH-treated group received 0.5μg/kg of GnRH, and those in the control group received an equivalent volume of saline. The bucks were bled 1 and 2 hours later to establish GnRH-stimulated levels. At 12 months of age, bucks were castrated, and testes were weighed and prepared for histological analysis. GnRH-stimulated concentration of T was correlated with yearling testicular diameter (r = 0.422, p<0.01). GnRH-stimulated FSH was found to be significantly (p<0.01) strongly positively associated (r=0.761, p<0.01) with the size of the yearling testis. Baseline FSH exhibited a negative association (r = -0.197, p<0.01) with Sertoli cells, and a weakly positive relationship (r = 0.235, p<0.01) with the amount of round spermatids. There was no discernible change (p<0.05) in their testes diameters: 24.52±0.43 mm (GnRH-treated group) and 25.92±0.45 mm (control group). Their yearling testicular mass varied significantly (p<0.05) between the GnRH-treated group (41.505.80 g), and the control group (38.807.58 g). The number and make-up of the seminiferous tubular cells (Sertoli cells, spermatogonia, spermatocytes, spermatids, and spermatozoa) indicate increased spermatogenesis in the GnRH-treated group. From this study, it is concluded that spermatozoa production in the West African dwarf buck is increased by GnRH superstimulation.