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High proliferative activity in the ovarian surface epithelial (OSE) layer, sometimes leading to cancerous growth, is believed to be associated with multiple ovulation and the resultant mitogenic effect of hormones at the site of ovulation. Estrous (cycling), anoestrous and pregnant ewes were selected in this study to evaluate whether OSE and follicular granulocyte cells’ proliferation is affected by the reproductive stages of the animal.
For this purpose, the level of proliferation was tested immunohistochemically using two nuclear protein markers, PCNA and Ki-67. Further, based on the morphological appearance of granulosa cells, the frequency of primordial, transitory, primary, preantral, and antral follicles was determined in the three groups of animals. Photomicrographs of the OSE layer revealed disorganized cells only in estrous ewes over corpus luteum. The same group also presented high Ki-67 immunoreactivity in the OSE layer indicative of high proliferative response. PCNA staining was also detectable in the OSE layer but at all follicular developmental stages, which suggests that, unlike the Ki-67 marker, this marker does not necessarily recognize the cell multiplication-related DNA synthesis activity.
In all the reproductive groups, the granulosa cells of primary, preantral and antral but not the primordial and transitory follicles exhibited a varying degree of immunostaining with PCNA, the maximum being in cycling animals. When the Ki-67 marker was used, granulosa cells of primary follicles in the cycling, and more differentiated follicles in all the groups reacted positively. The frequency of different follicles also varied in the three groups.
While primordial and transitory follicle counts were nearly similar in each group of the animals, the frequency of preantral and antral follicles was lower in the pregnant than in the anoestrous and cycling groups. Within this low percentage to the size of the antral follicle also varied significantly in the three groups. The small antrum (<2 mm and 2-3 mm) were uniformly present in all the animals but the larger ones (3-4 and 4-5 mm) were nearly absent in the pregnant ewes.
We discussed the role of progesterone produced in the corpus luteum in suppressing follicular development during pregnancy. The antrum before maturing becomes atretic. In anoestrous ewes, estrogen may have an overriding effect on progesterone and follicular development goes on normal, especially the antrum attains normal size. It is in the cycling animals, were due to frequent ovulation, the OSE cells in proximity to ovulating follicle or post-ovulating corpus luteum exhibit massive proliferative activity and disorganized colonization. In the normal course, this may lead to epithelial regeneration in the wounded site, but if exposed to mitogenic or inflammatory agents, these cells may transform neoplastic.
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