Effects of Follicular Fluid and Serum Supplementation on Cumulus Cell Expansion and Nuclear Progression of Guinea Pig Oocytes, Using a Baseline Medium Established with Bovine Oocytes

Abstract

This study evaluated the effects of serum (egpS) and follicular fluid (egpFF) from estrus guinea pigs as in vitro maturation (IVM) supplements for natural cycle guinea pig oocytes. Two experiments were conducted: the first assessed three IVM media, a commercial medium (CMOM) and two homemade media (HMOM-P and HMOM-S), for oocyte in vitro maturation using 615 bovine oocytes, while the second evaluated the incorporation of 5%, 10%, and 20% egpFF or egpS into IVM media for 1744 guinea pig oocytes. Initially, we optimized the IVM base medium using bovine oocytes to determine the most suitable culture conditions. The results obtained from these experiments served as a critical foundation for subsequent supplementation trials conducted with guinea pig oocytes. The oocytes were cultured in 70 μL drops under controlled atmospheric conditions, and maturation rates were assessed based on cumulus cell expansion and nuclear progression. The HMOM-S medium significantly enhanced cumulus cell expansion (72.5 ± 2.88%) compared with the CMOM medium (57.7 ± 5.33%; p < 0.05). Supplementation with egpFF at 5% (68.8 ± 6.22%), 10% (76.3 ± 5.39%), and 20% (80.9 ± 6.22%) significantly improved both cumulus cell expansion and nuclear progression in high-quality oocytes (types A and B), compared to the control group (43.3 ± 4.82%). Conversely, supplementation with egpS did not have a significant effect on cumulus cell expansion (p > 0.05); however, it notably improved nuclear maturation in low-quality oocytes (type C) at concentrations of 10% and 20% (p < 0.05). This resulted in an overall improvement in maturation outcomes, particularly for oocytes with compromised initial quality. These findings demonstrated that the IVM of guinea pig oocytes using HMOM-S medium was significantly enhanced by the presence of egpFF, whereas egpS supplementation exhibited a less pronounced effect on IVM outcomes.

Keywords: estrous guinea pig follicular fluid (egpFF); estrous guinea pig serum (egpS); guinea pig; in vitro maturation; oocyte.

Figure 1

Different degrees of expansion of cumulus cells of bovine oocytes matured in vitro for 24 h. The degree of cumulus cell expansion was classified into three grades: (A) non-expanded cumulus (N-EC), (B) partially expanded cumulus (P-EC), and (C) totally expanded cumulus (T-EC).

Figure 2

Evaluation of cumulus cell expansion of oocyte bovine based on the classification of the degree of expansion achieved 24 h after treatment with three in vitro maturation media: CMOM (Commercial Medium for Oocyte Maturation), HMOM-P (Homemade Medium for Oocyte Maturation—Primary), and HMOM-S (Homemade Medium for Oocyte Maturation—Secondary). The degree of cumulus cell expansion was classified according to three grades: N-EC (non-expanded cumulus), P-EC (partially expanded cumulus), and T-EC (totally expanded cumulus). Different lowercase letters (a, b) indicate significant differences between treatment for each degree of expansion of cumulus cells (p < 0.05).

Figure 3

Evaluation of bovine oocyte in vitro maturation rates based on the progression from the germinal vesicle stage (GV) to metaphase II (M-II), assessed 24 h post-treatment with three distinct in vitro maturation media: CMOM (Commercial Medium for Oocyte Maturation), HMOM-P (Homemade Medium for Oocyte Maturation—Primary), and HMOM-S (Homemade Medium for Oocyte Maturation—Secondary).