Immunohistochemical assessment of cellular proliferation in multioocyte follicles from Bos indicus ovaries

The objective of this study was to evaluate by immunohistochemistry cellular proliferation in multioocyte follicles from bovine adult ovaries. Ovaries (n=12) from Nelore heifers obtained at a slaughterhouse were fixed in Bouin and submitted to histological processing. Slides were prepared in duplicate (PAS staining-Schiff and Immunohistochemistry) with sections of 5 µm. Screening for multioocyte follicles was performed on PAS stained slides. All multioocyte follicles were submitted to immunohistochemistry with anti-PCNA (Clone PC1O, ZYMED® Laboratories). The level of PCNA-positive cell proliferation was assessed in granulosa cells (score ranging from one to four) and oocytes (qualitative assessment). Data were evaluated only for qualitative aspects and therefore will not be expressed numerically. Data were subjected to ANOVA (p ≤ 0.05). From 12 ovaries examined, we found 12 multioocyte follicles, containing from two to three oocytes. These structures were found predominantly in primordial follicles (n = 10) and primary follicles. There was no difference (p > 0.05) in cell proliferation of granulosa cells from primordial and primary follicles. However, there was a trend of increase in mitotic activity of granulosa cells from follicles multioocyte compared to other follicles. For the mitotic activity in oocytes, PCNA immunostaining was positive in follicles at different stages of development. Immunostaining was stronger in oocytes from multioocyte follicles (p < 0.05), reinforcing the proposition that multioocyte follicles are in constant proliferation. Based on these results, we concluded that adult Bos taurus indicus cattle present multioocyte follicles in early stages of development. The oocytes enclosed in multioocyte follicles do not display the same pattern of PCNA immunostaining, suggesting they are in different stages of development and/or there is some kind of competition or dominance between them.