Tumor necrosis factor α (TNFα) is a multifunctional cytokine present in oocytes and macrophages in the neonatal rat ovary. The presence of both TNFα and its receptors in the neonatal rat ovary suggests a potential role for it in follicle assembly or oocyte atresia. Previous studies have provided support for effects of TNFα on isolated granulosa and theca cells and intact follicles; however, to our knowledge, this is the first study to investigate the effects of TNFα on the earliest stages of follicular development. Effects of TNFα on oocyte/follicle number and apoptosis were investigated using an ovarian organ-culture system that supported assembly of primordial follicles in vitro. Ovaries were collected on the day of birth and treated with TNFα (0, 0.1, 1.0, 10, or 50 ng/ml), a function-blocking TNFα antibody (5 μg/ml), or control immunoglobulin (Ig) G. At 1 ng/ml, TNFα decreased follicle and oocyte numbers during 3 days of culture, whereas higher (10 and 50 ng/ml) or lower (0.1 ng/ml) doses had no effect. Treatment with TNFα antibodies increased the number of oocytes and follicles compared to nonspecific IgG control. To determine whether the decreased oocyte/follicle numbers were due to an apoptotic effect of TNFα, apoptosis was examined by DNA laddering. At 1 ng/ml, TNFα increased apoptotic DNA laddering twofold, with no significant effect from lower or higher doses. The cells undergoing apoptosis, as determined by in situ end-labeling, were oocytes, interstitial cells, and granulosa cells. These findings suggest that TNFα may be involved in oocyte atresia that normally occurs during the perinatal period.
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