325 VIABILITY AND GROWTH OF CATTLE PREANTRAL FOLLICLES AFTER IN VITRO CULTURE OF OVARIAN FRAGMENTS IN α-TOCOPHEROL

Abstract

The development of culture systems to support the initiation of growth of primordial follicles is important to the study of the factors that control the earliest stages of folliculogenesis. The aims of the present study were to investigate the effects of α-tocopherol on survival, activation, and growth of cattle preantral follicles using histological and immunohistochemistry proliferating cell nuclear antigen (PCNA) studies. The ovarian cortex was divided into small fragments; one fragment was immediately fixed in Bouin (control). The other fragments were cultured for 2, 4, 6, or 8 d in culture plates with Minimum Essential Medium supplemented with insulin-transferrin-selenium (ITS), pyruvate, glutamine, hypoxanthine, BSA, and antibiotics (MEM+); and MEM+ plus α-tocopherol (5, 25, 50, 100, or 200 ng mL^-1). Preantral follicles were classified according to their developmental stage (primordial, intermediate, primary, or secondary) and on the basis of morphological features (normal or degenerated). Pair-wise comparisons were done using Tukey’s procedure. Chi-square test was used to compare the percentage of follicles with PCNA-positive granulosa cells. All analyses were done with the SAS software (SAS Institute, Cary, NC, USA), and P < 0.05 was considered significant. The results showed that, compared with non-cultured cortical tissue (Day 0), the culture of ovarian tissue significantly reduced (P < 0.05) the percentage of normal follicles in all media tested, except for tissue cultured in the presence of 200 ng mL^-1 of a-tocopherol. Furthermore, in all media tested, the percentage of primordial follicles was significantly reduced (P < 0.05), with a concomitant increase in the percentage of developing follicles. The highest percentage of secondary follicles was observed after 6 days of culture in MEM plus 200 ng mL^-1 of a-tocopherol. The PCNA analysis confirmed the viability of follicles cultured with 200 ng mL^-1 of a-tocopherol after 6 d. After 8 days of in vitro culture, we observed severe follicular degeneration in all media tested, suggesting that other supplements are recommended for longer periods of culture. In conclusion, the results of the present study indicate that 200 ng mL^-1 of a-tocopherol maintains the survival of cattle preantral follicles and promotes activation of primordial follicles after 6 days of in vitro culture.

Financial support: L. A. Lisboa is a recipient of CAPES support; E. R. Andrade and A. A. Alfieri are recipients of PRODOC/CAPES fellowships.