Antifertility Activity of Quassia amara: Quassin Inhibits the Steroidogenesis in Rat Leydig Cells In Vitro - Njar, Vincent C O; Alao, Taiwo O; Okogun, Joseph I; Raji, Yinusa; Bolarinwa, Adeyombo F; Nduka, Ebere U (Planta Medica, 1995)