219 Use of a genetically-engineered swine line to elucidate the role of GnRH-II and its receptor in gilts

Abstract

Abstract The second form of GnRH (GnRH-II) and its receptor (GnRHR-II) are produced in only one livestock species, the pig. Paradoxically, their interaction does not stimulate gonadotropin secretion. Instead, both have been implicated in autocrine/paracrine regulation of steroidogenesis. To elucidate their role in ovarian function, our laboratory generated transgenic swine with ubiquitous knockdown (KD) of GnRHR-II. Blood samples were collected from GnRHR-II KD (n = 8) and littermate control (n = 7) gilts at the onset of estrus (follicular) and 10 d later (luteal). Serum samples were subjected to HPLC-MS/MS to quantify concentrations of 16 steroid hormones. At euthanasia, ovarian weight, ovulation rate and weight of each excised corpus luteum (CL) were recorded; HPLC-MS/MS was also performed on CL tissue. A line (GnRHR-II KD versus control) x phase (follicular versus luteal) interaction was detected for serum progesterone concentrations; levels were reduced in transgenic compared with control gilts during the luteal phase (P = 0.0329). A tendency for a line effect was observed for 11-deoxycorticosterone and 11-deoxycortisol; transgenic females tended to produce less of these corticosteroids (P < 0.10). A phase effect was detected for cortisone, 11-deoxycortisol, cortisol, corticosterone, androstenedione, androsterone, testosterone, estrone and 17β-estradiol (P < 0.05); concentrations were greater in follicular versus luteal samples (P < 0.05). Conversely, 17α-hydroxyprogesterone concentrations were elevated in luteal samples (P < 0.05). Ovarian weight did not differ between lines, although ovulation rate was reduced in GnRHR-II KD versus control gilts (P = 0.0123). However, average CL weight was greater in GnRHR-II KD compared with control females (P < 0.0001); therefore, total CL weight tended to be reduced in transgenic gilts (P = 0.0958). In tissue samples, concentrations of progesterone and estrone tended to be reduced in transgenics females (P ≤ 0.10). Ultimately, these data suggest that GnRH-II and its receptor may help regulate ovulation rate, CL development and progesterone production in gilts. Supported by USDA/NIFA AFRI-ELI predoctoral fellowship (2017-67011-26036; ATD) and AFRI (2017-67015-26508; BRW) funds.