Effects of human serum on rat cumulus-oocyte complex functions in vitro: Oocyte activation and endocrine secretions

Secretion of hormones and oocyte meiotic events were assessed following in vitro culture of ovulated rat cumulus-oocyte complexes (COCs) in media containing different types of human serum. Both toxic and nontoxic (determined by mouse embryo test) samples of fetal cord or adult female serum were utilized for these experiments. After short-term culture (4.5 hr), with or without COCs, medium containing 10% serum was collected and analyzed for its content of estradiol, progesterone, and prostaglandin E (PGE), and oocytes were cytologically evaluated for spontaneous activation (second polar-body extrusion). Activation of oocytes occurred in all media tested. Steroids (progesterone and estradiol) levels were markedly elevated in culture medium containing cord serum as compared to medium containing adult female serum. The progesterone content of culture medium decreased after incubation of COCs with cord serum and increased when incubated with adult female serum. Little or no prostaglandin was detected in any control media. However, COCs secreted prostaglandin during culture in all media. COCs secreted estradiol when cultured in medium containing cord but not adult female serum. Results demonstrate that two types of serum utilized for in vitro culture of COCs varied markedly in their hormone content and differentially affected the secretion of hormones by COCs during culture. The results are discussed in relation to the success of IVF procedures.