Radioimmunoassay of follistatin: application for in vitro fertilization procedures.

A sensitive radioimmunoassay (RIA) for follistatin was developed by using antisera raised in rabbits against purified porcine ovarian follistatin. The displacement curves generated with human follicular fluid and serum were parallel with the standard curve of porcine follistatin. Using this RIA, we have measured human serum follistatin immunoreactivity in six women undergoing ovarian hyperstimulation for in vitro fertilization (IVF). After treatment with a GnRH agonist and gonadotropin, serum estradiol and follistatin levels were increased, and there was a direct positive correlation between the elevated levels of estradiol and follistatin (r = 0.93, p less than 0.01). Thus, the level of circulating follistatin may likely reflect follicular maturation and be applicable in IVF procedures to determine the optimal timing for oocyte retrieval.