Relationship between Amino Acid Metabolism and Bovine In Vitro Follicle Activation and Growth

SIMPLE SUMMARY: Bovine ovaries at all ages contain high numbers of immature eggs (oocytes) contained in follicles, but only a small proportion will ever be ovulated, with the rest destined to degenerate. In vitro growth (IVG) is a culture technique to support the development of immature oocytes/follicles in vitro. Bovine primordial follicles can be grown in vitro to the antral stage, but further optimization of the culture system is required to support development to maturity and fertilization. The present study focuses on the amino acid metabolism of early-stage bovine follicles during IVG to determine whether this can be correlated with development to provide a non-invasive marker of follicle health in vitro. The results indicate possible candidate amino acids and metabolites as potential markers of health status for in vitro-grown follicles. ABSTRACT: The amino acid metabolism of bovine follicles during in vitro growth (IVG) was evaluated to identify potential indicators of health during culture. The bovine ovarian cortex was sliced, prepared as strips, and cultured for 6 days. Tissue samples were examined histologically before and after 6 days of culture, and the degree of follicle activation was classified as either high or low based on the number of growing secondary follicles present (high: 7~11; low: 0~1). In a separate experiment, secondary follicles (diameter range: 100~200 μm) were manually isolated and cultured, and their growth was monitored for 6 days. Cultured follicles were classified as growth or degenerate based on diameter change during culture (growth: +60.5~74.1 μm; degenerate: −28~15.2 μm). Free amino acids and their metabolites were measured in the spent culture medium from each group. In cultured ovarian cortical strips, the concentration of α-aminoadipic acid was significantly higher in the low activation group than in the high group (p < 0.05), while those of methionine, lysine, and arginine were higher in the high activation group. In cultured isolated secondary follicles, concentrations of methionine, tyrosine, histidine, and hydroxyproline were higher in the degenerate group (p ≤ 0.05). In conclusion, amino acid metabolism has the potential to serve as an indicator of primordial follicle activation and subsequent growth rate during bovine IVG.