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Sequential changes in androgen receptor (AR) distribution were investigated in rat ovarian follicles during their physiological development. Mature female Wistar rats, exhibiting a regular 4-day oestrous cycle, were killed in succession on the day of oestrus, metoestrus, dioestrus, and pro-oestrus. Excised ovaries were submitted to immunohistochemical procedure in which polyclonal androgen receptor antibody, avidin-biotin-peroxidase complex, and DAB were used. Strong AR immunostaining was located predominantly in the nuclei of the granulosa layer of preantral and very early antral follicles, present in the ovaries at all stages of the oestrous cycle. At early oestrus a decline in AR was noted in the mural granulosa cells of presumably recruited early antral follicles. The decline involved the area of appearing pseudostratification. During metoestrus and dioestrus AR decline proceeded towards the antrum, but the antral regions connected with COC by strings of granulosa cells or lying in close proximity to COC were always strongly AR-positive. It was only on the day of pro-oestrus that AR was confined to COCs and a few antral cells bordering the antrum. These findings indicate that during the oestrous cycle AR decline starts in the mural granulosa cells of oestrous antral follicles beginning to differentiate and is completed at pro-oestrus, but even before ovulation it does not extend to COC. The persistence of AR immunostaining in the latter region suggests that androgens can play here a paracrine role especially before ovulation. Atretic follicles showed a different pattern of AR distribution, dependent on their stage of development and the advancement of this process.

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