The mechanisms that regulate the gradual exit of ovarian follicles from the nongrowing, primordial pool are poorly understood. The objective of this study was to evaluate the effects of adding ascorbic acid to the media for in vitro culture of cattle ovarian fragments and to determine the effects of this addition on the growth activation and viability of preantral follicles. The ovarian cortex was divided into small fragments; 1 fragment was immediately fixed in Bouin’s solution (control). The other fragments were cultured for 2, 4, 6, or 8 days on culture plates in minimum essential medium (MEM) supplemented with insulin-transferrin-selenium (ITS), pyruvate, glutamine, hypoxantine, BSA, and antibiotics (MEM+) or in MEM+ plus ascorbic acid (5, 25, 50, 100, or 200 μg mL-1). Ovarian tissue was processed for classical histology, TEM, and immunohistochemical demonstration of proliferating cell nuclear antigen (PCNA). Preantral follicles were classified according to their development stage (primordial, intermediate, primary, and 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 percentages of follicles with PCNA-positive granulosa cells. All analyses were done with Statistical Analysis System (SAS Institute, Cary, NC, USA); P ≤ 0.05 was considered significant. Compared with control fragments, the percentage of primordial follicles was reduced (P ≤ 0.05) and the percentage of growing follicles was increased (P ≤ 0.05) in cultured cortical fragments, independent of the tested medium or incubation time. Furthermore, compared with control tissue, culture of ovarian cortex for 8 days reduced the percentages of healthy, viable follicles (P ≤0.05), but not when cultures were supplemented with 25, 50, and 100 μg mL-1 of ascorbic acid. Ultrastructural and immunohistochemical analysis of ovarian cortical fragments cultured for 8 days, however, showed the integrity and viability of follicles only when fragments were cultured in the presence of 50 μg mL-1 of ascorbic acid. In conclusion, this study demonstrated that addition of ascorbic acid to MEM at a concentration of 50 μg mL-1 not only stimulates the activation and subsequent growth of cattle primordial follicles that are cultured in vitro for 8 days but also safeguards the viability of these preantral follicles.
E. R. Andrade and A. A. Alfieri are recipients of the PRODOC/CAPES fellowship.
Transforming growth factor-β (TGF-β) maintains follicular ultrastructure and stimulates preantral follicle growth in caprine ovarian tissue cultured in vitro
