243 Relationship Among Granulosa Cell Gnrh-i, -II, and Receptor Mrna Abundance and Follicular Fluid Steroid Hormone Concentrations of Bovine Antral Follicles at Specific Stages of Follicular Development

Abstract

Abstract Transcript abundance of two forms of GnRH and its receptor have been characterized in bovine ovaries. The objective was to investigate the relationship of GnRH-1, GnRH-2, GnRH-R, intrafollicular estradiol (E2) and progesterone (P4) during follicular development. Ovaries were collected from beef cows at specific stages of follicular development [pre-selection (PRE, n = 9), post-selection (POST, n = 9), and post-selection 24h after luteal regression (PG, n = 9)]. The largest follicle per stage was aspirated to obtain granulosa cells (GC) and follicular fluid (FF). Total cellular RNA was extracted from GC and RT-PCR was performed for GnRH-1, GnRH-2, GnRH-R and GAPDH. Radioimmunoassays were performed to determine FF concentrations of E2 and P4. Data were analyzed using the MIXED and REG procedures in SAS. There was no difference (P ≥ 0.23) in mRNA abundance of GnRH-2, GnRH-R or FF concentrations of P4 across follicular stages. There was an effect of stage on FF E2 (PRE: 17,925±20,273, POST: 28,458±21,503, and PG: 252,616±21,503 pg/mL; P < 0.01). Stage affected GnRH-1 mRNA abundance (PRE: 2.28±0.55, POST: 0.92±0.55, and PG: 0.11±0.55; P = 0.03). There was no relationship of GnRH-1 and GnRH-2 mRNA abundance or effect of FF P4 on GnRH-R mRNA abundance (P ≥ 0.23). There was no effect of FF P4 on GnRH-1 mRNA abundance (P = 0.68). There was no effect of FF E2 on GnRH-2 mRNA abundance (P = 0.66). As FF E2 increased GnRH-R mRNA abundance tended to increase (P = 0.10;r2=0.13). As FF P4 concentrations increased GnRH-2 mRNA abundance tended to decrease (P = 0.09;r2=0.12). As FF E2 increased GnRH-1 mRNA abundance decreased (P = 0.02;r2=0.20). In conclusion, there were differences in peptide and receptor mRNA abundance of GnRH in relation to FF E2 and P4 at specific stages of follicular development. This is supportive of a regulatory relationship between ovarian GnRH and steroidogenesis. This work is supported by AFRI Grant No.2018-67016-27578 from USDA. USDA is an equal opportunity provider and employer.