A Granulosa Cell Differentiation-Stage-Specific Cytotoxic Activity in Bovine and Rat Sera1

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Abstract
Heat-inactivated serum is cytotoxic to granulosa cells from preantral follicles but not to cells from preovulatory follicles. A dominant feature of the granulosa cells of preovulatory follicles is the presence of luteinizing hormone (LH) receptors on the surface of the cells. In the present study, we have examined the relationship between the process of LH receptor induction and the acquisition of serum tolerance in granulosa cells in vitro. Granulosa cells from the ovaries of immature rats primed with diethylstilbestrol (DES) were cultured in a 1:1 mixture of Ham''s F-12 and Dulbecco''s modified Eagle''s medium containing 30 ng of ovine follicle-stimulating hormone (oFSH; NIH-15). At either 0, 24, or 48 h of culture, heat-inactivated fetal bovine serum (FBS) was added (10% by volume) to separate groups of culture tubes. All cells were cultured for a total of 72 h, at which time the cultures were assessed for LH receptor (specific 125I-human chorionic gonadotropin [hCG] binding) and DNA content. LH receptors were induced in all FSH-containing serum-free cultures by 48 h. Receptors were not induced, however, when serum was added after either 0 or 24 h of culture. Furthermore, serum addition at these times resulted in a cell loss (assessed by DNA) of 40-60%. Serum addition at 48 h to FSH-containing cultures resulted in a inability to detect LH receptors at 72 h and with no significant effect on the culture DNA content. Addition of a protein extract of FBS at the initiation of cell culture prevented FSH-stimulated LH receptor induction and was cytotoxic. A lipid extracts of FSH did not interfere with receptor induction and was not cytotoxic. Rat serum shows the same activities as FSB. The addition of soybean trypsin inhibitor to serum-containing cultures blocked both the cytotoxic and LH receptor inhibitory activities. The addition of estradiol to cell cultures also protected against serum actions. We speculate that these deleterious effects of serum, which are modulated by estrogen, may play a significant role in the prosess of follicular atresia.

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