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Title: Effect of gonadotropin-releasing hormone II receptor (GnRHR-II) knockdown on testosterone secretion in the boar

item DESAULNIERS, AMY - University Of Nebraska
item CEDERBERG, REBECCA - University Of Nebraska
item MILLS, GINGER - University Of Nebraska
item WHITE, BRETT - University Of Nebraska
item Lents, Clay

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/6/2016
Publication Date: 7/16/2016
Citation: Desaulniers, A., Cederberg, R., Mills, G., White, B., Lents, C. 2016. Effect of gonadotropin-releasing hormone II receptor (GnRHR-II) knockdown on testosterone secretion in the boar [abstract]. Society for the Study of Reproduction Annual Meeting. Abstract # 483 (Scientific Program p. 86). Available:

Interpretive Summary:

Technical Abstract: Unlike the classical gonadotropin-releasing hormone (GnRH-I), the second mammalian GnRH isoform (GnRH-II; His5, Trp7, Tyr8) is a poor stimulator of gonadotropin secretion. In addition, GnRH-II is ubiquitously expressed, with transcript levels highest in tissues outside of the brain. A receptor specific to GnRH-II (GnRHR-II) has been identified in mammals; however, gene coding errors prevent the production of a full-length protein in many species. Instead, GnRH-II acts through the GnRH-I receptor in these species. In contrast, GnRHR-II is functional in swine, allowing our laboratory to examine its role in porcine testicular function. We observed that GnRH-II and its receptor are most abundant within the testis compared to the hypothalamus and anterior pituitary gland, respectively, suggesting a key role in porcine testicular function via autocrine/paracrine interactions. Further, immunoreactive GnRHR-II was detected on porcine Leydig cells and GnRH-II treatment stimulated testosterone secretion from testicular cultures. Moreover, GnRH-II stimulated testosterone synthesis as effectively as GnRH-I in vivo, despite minimal secretion of the classical androgen stimulator, luteinizing hormone (LH). Thus, we hypothesized that GnRH-II acts directly on Leydig cells to stimulate steroidogenesis, independent of LH secretion. To further examine the function of GnRH-II and its receptor within the porcine testis, we produced a GnRHR-II knockdown (KD) swine line. The objective of this study was to compare testis volume and serum testosterone levels in transgenic and littermate control males during pubertal development. GnRHR-II KD (n = 10) and littermate control (n = 7) boars were monitored throughout development; blood was collected and testis size measured using calipers at 40, 100, 150, 190, 225 and 300 d of age. Predicted testis volume was calculated [volume = 3/4(pi)(L/2)(W/2)**2, where L = testis length and W = testis width] and serum testosterone concentrations were quantified by radioimmunoassay. No line (transgenic or control) x age interaction (P = 0.6110) or line (P = 0.1406) effects on body weight were observed, indicating that transgenic and littermate control boars had a similar body weight. Interestingly, there was an effect of line (P = 0.0466) for predicted testis volume; GNRHR2 KD boars had smaller testes (331.8 ± 13.9 cm**3) than littermate controls (374.8 ± 17.2 cm**3) overall. There was an age effect (P < 0.0001) for testes volume, but no line x age interaction (P = 0.3910). Although there was no line x age interaction (P = 0.3872) for serum testosterone concentrations, there was a tendency (P = 0.0586) for an effect of line as well as an age effect (P < 0.0001). Overall, transgenic boars tended (P = 0.0586) to have lower serum testosterone concentrations (1.6 ± 0.9 ng/ml) than littermate control boars (4.2 ± 1.0 ng/ml). These data indicate that GnRHR-II KD reduces testis volume and decreases serum testosterone levels in the boar, supporting the hypothesis that GnRHR-II is involved in regulating steroidogenesis within the porcine testis. Partially supported by NIFA Hatch (NEB-26-199; BRW) and AFRI (2011-67015; CAL) funds.