17,20β,21-Trihydroxy-4-pregnen-3-one

17,20β-Dihydroxy-4-pregnen-3-one (17α,20β-DP) and 17,20β,21-Trihydroxy-4-pregnen-3-one (20β-S) are identified as maturation inducing steroids in teleost fish. 20β-S is produced from 11-deoxycortisol by 20β-hydroxysteroid dehydrogenase (20β-HSD) in ovarian follicular cells under the influence of pituitary gonadotropin. It stimulates the meiotic maturation of oocytes during GVBD. Biological actions of these steroids are mediated by both membrane and nuclear receptors.