Location: Livestock Bio-SystemsTitle: GnRHR-II knockdown swine have constitutively lower serum testosterone concentrations, impaired senstitivity to GnRH analogues and reduced semen quality
|DESAULNIERS, A - University Of Nebraska|
|CEDERBERG, R - University Of Nebraska|
|KNOX, R - University Of Illinois|
|WHITE, B - University Of Nebraska|
Submitted to: Pig Reproduction National Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2017
Publication Date: 6/11/2017
Citation: Desaulniers, A.T., Cederberg, R.A., Knox, R.V., Lents, C.A., White, B.R. 2017. GnRHR-II knockdown swine have constitutively lower serum testosterone concentrations, impaired senstitivity to GnRH analogues and reduced semen quality. [Abstract] In: Proceedings of the 10th International Conference on Pig Reproduction, University of Missouri, Columbia, MO. 11-14 June 2017. Poster. p. 94-95. Available: http://muconf.missouri.edu/ICPR2017.
Technical Abstract: The second mammalian GnRH isoform (GnRH-II) and its specific receptor (GnRHR-II) are abundantly produced within swine testes. GnRHR-II localizes to porcine Leydig cells and exogenous GnRH-II treatment robustly stimulates testosterone production in vivo, despite minimal secretion of luteinizing hormone (LH). These data indicate that GnRH-II directly effects testicular steroidogenesis. To explore this hypothesis, we produced a line of GnRHR-II knockdown (KD) swine that expresses 70% less testicular GNRHR2 mRNA than littermate controls. During pubertal development, testosterone concentrations were reduced in transgenic males whereas LH was unaffected. In addition, testosterone secretion was constitutively lower in adult GnRHR-II KD animals during an 8 h sampling period. The responsiveness of mature GnRHR-II KD (n = 5) and littermate control (n = 5) males to GnRH analogues was compared using boars surgically fit with indwelling jugular cannulae. In the first trial, blood was serially collected prior to intramuscular injection with the GnRHR antagonist, SB-75 (10 µm/kg BW). Blood was sampled for 36 h after treatment and serum testosterone concentrations were quantified by radioimmunoassay. A time by treatment interaction (P = 0.012) was observed. Prior to treatment, testosterone levels were lower (P < 0.05) in transgenic boars. Testosterone levels were suppressed below basal concentrations in both transgenic and control boars at 1.5, 2, 2.5, 3 and 12 h after SB-75 treatment. However, testosterone levels in transgenic males remained lower (P < 0.05) than controls during SB-75-induced testosterone suppression. Given that testosterone levels were lower in transgenics at the initiation of the trial, these data indicate that SB-75 was less effective at suppressing testosterone secretion from the testes of GnRHR-II KD animals. In the next trial, blood was serially collected prior to treatment with either D-Ala6 GnRH-I or D-Ala6 GnRH-II (150 ng/kg of body weight) and for 310 min thereafter, in a crossover design with 1 wk between treatments. There was a line by time by treatment interaction (P < 0.05). At the initiation of the trial, testosterone levels were lower in transgenic boars (P < 0.05). After treatment with either D-ala6 GnRH-I or -II, testosterone concentrations began to increase, although the response was not uniform. Control boars treated with D-ala6 GnRH-I were most responsive to treatment whereas GnRHR-II KD boars treated with GnRH-II were least responsive. In order to determine if reduced testosterone secretion in GnRHR-II KD boars has a biological consequence on fertility, ejaculates were collected from GnRHR-II KD (n = 6) and littermate control (n = 5) males and subjected to computer-assisted semen analysis (CASA; IVOS; Hamilton Thorne, Beverly, MA). Both sperm concentration (87.9 ± 13.4 million cells/ml) and percent motility (64.8 ± 7.6%) tended (P = 0.10) to be reduced in GnRHR-II KD compared to littermate control boars (118.6 ± 14.3 million cells/ml and 86.2 ± 8.35%, respectively). These data: 1) confirm that GnRHR-II KD boars constitutively produce less serum testosterone; 2) demonstrate that GnRHR-II KD boars are less responsive to GnRH analogues; and 3) further highlight the importance of GnRH-II and its receptor in the regulation of steroidogenesis within the boar testis.