Improved in vitro bioassay of follitropin

The FSH-dependent aromatase activity of Sertoli cell enriched cultures of testicular cells from immature rats was utilized as a sensitive and specific in vitro bioassay for FSH activity. The conversion of 19-hydroxyandrostenedione to estradiol was used as the end point of the assay. By the introduction of a phosphodiesterase inhibitor into the culture medium, the sensitivity was improved 5-10 times, so that 0.05 mIU of FSH showed a response significantly different from the blank. Other pituitary or placental hormones, such as hLH, hTSH and hCG exhibited less than 0.8% cross-reactivity, whereas hGH, hPRL, ACTH1-24, LH-RH, and prostaglandin E2 alpha did not show any cross-reaction at the doses tested.