Luteinizing hormone secretion in GnRHR-II knockdown boars

Authors: DESAULNIERS, AMY - University Of Nebraska; CEDERBERG, REBECCA - University Of Nebraska; Lents, Clay; WHITE, BRETT - University Of Nebraska

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/28/2020
Publication Date: 7/1/2020
Citation: Desaulniers, A.T., Cederberg, R.A., Lents, C.A., White, B.R. 2020. Luteinizing hormone secretion in GnRHR-II knockdown boars [abstract]. Society for the Study of Reproduction Annual Meeting. Abstract Program p. 51, No.2348. Available: https://higherlogicdownload.s3.amazonaws.com/SSR/fbd87d69-d53f-458a-8220-829febdf990b/UploadedImages/Abstract_Book_Complete_Final_2.pdf

Interpretive Summary:

Technical Abstract: The second mammalian form of GnRH (GnRH-II) and its receptor (GnRHR-II) are produced in only one livestock species, the pig. Paradoxically, the physiological interaction of GnRH-II with its receptor does not stimulate gonadotropin secretion. Instead, both are abundantly produced within the testis and have been implicated in autocrine/paracrine regulation of steroidogenesis. To further study the role of GnRH-II and its receptor, our laboratory generated a transgenic swine line with ubiquitous knockdown (KD) of GnRHR-II; expression is reduced by 70% within the testes of transgenic males and serum concentrations of 10 gonadal steroids (2 proestogens, 2 estrogens and 6 androgens) are reduced by 60-98%. The objective of this study was to assess luteinizing hormone (LH) secretion in mature GnRHR-II KD (n = 5) and littermate control (n = 5) males via a series of in vivo endocrine trials. In all experiments, blood was collected via indwelling jugular cannulae and serum concentrations of LH were measured via radioimmunoassay. In the first trial, diurnal secretory patterns of LH were assessed by sampling every 15 min for 8 h. There was an effect of time (P = 0.0008) but no effects for line (GnRHR-II KD versus control) or line by time interaction (P > 0.05). Pulse analysis of LH data revealed no differences between lines (P > 0.05); baseline, minimum and maximal concentrations as well as pulse frequency, pulse amplitude, pulse duration and area under the curve were similar between lines (P > 0.05). In the next trial, blood was serially collected prior to and after intravenous treatment with either D-Ala6 GnRH-I or D-Ala6 GnRH-II (150 ng/kg BW). A time by treatment interaction was detected (P = 0.0004); however, there was no line by time by treatment interaction (P = 0.6654). In control and transgenic animals treated with D-Ala6 GnRH-I, LH concentrations rose dramatically above baseline within 10 min post-treatment and remained elevated throughout the duration of sampling (270 min). In control and GnRHR-II KD boars treated with D-Ala6 GnRH-II, however, LH levels rose slightly above pretreatment concentrations within 10 min post-treatment and remained elevated for 40 min before returning to basal levels. In the third trial, blood was serially collected prior to and after intramuscular injection with the GnRHR antagonist, SB-75 (cetrorelix; 10 µm/kg BW). An effect of time was detected (P < 0.0001) but no effects of line or line by time interaction were evident (P > 0.05). In both transgenic and control males, LH levels were suppressed below baseline concentrations at 2, 2.5, 3, 6, 9 and 24 h post-injection (P < 0.05). These results provide further evidence that GnRH-II and its receptor are not physiological regulators of gonadotropin secretion in mammals; instead, attenuation of gonadal steroidogenesis in transgenic boars is likely due to reduced testicular expression of GnRHR-II. Supported by USDA/NIFA AFRI-ELI predoctoral fellowship (2017-67011-26036; ATD) and AFRI (2017-67015-26508; BRW) funds.