Mouse serum facilitates the expansion of the follicular cavity regardless of the estrous cycle phase.

OBJECTIVE: In investigating the effect of alcohol intake on the in vitro development of preantral follicles, physiological differences across estrous cycle phases in mice probably affect the results; therefore, it is necessary to determine whether serum effects vary depending on the estrous cycle phase. DESIGN: Serum derived from different estrous phases was used as a treatment group, and fetal bovine serum (FBS) was used as a control group for comparison. Samples containing 10% mice serum from different estrous phases and FBS in medium were used to culture preantral follicles. The development of preantral follicles was assessed by morphology and at the cellular and molecular levels. SUBJECTS: KM adult female mice and female mice at 10 d of age. Mouse sera were collected at different phases (proestrus, estrus, metestrus, and diestrus) during the estrous cycle. MAIN OUTCOME: Measurement of follicular growth and development, including the follicular cavity area, granularity, and cell viability. Assessment of reactive oxygen species (ROS) levels and the mitochondrial membrane potential. Comparison of the chemical compositions of mouse sera and FBS by GC‒MS. RESULTS: Compared with FBS, mouse serum did not significantly affect in vitro development of preantral follicles at any of the four phases of the estrous cycle. However, serum derived from different estrous cycle phases significantly increased the follicular cavity area, whereas the level of reactive oxygen species increased and the mitochondrial membrane potential decreased. GC‒MS detection revealed that both mouse serum and FBS contained more than 800 substances, among which 14 components with mass‒charge ratios exceeding 80 were identical. The fatty acid content in mouse serum was greater than that in the FBS group, and cholesterol components were not detected in the FBS group. CONCLUSION: The in vitro development of preantral follicles was not affected by the estrous cycle phase. However, serum from each phase of the estrous cycle plays an important role in regulating the formation of the follicular cavity, and this process is likely executed by cholesterol, which provides a reference for future studies on the in vitro development of follicles.