Nomegestrol acetate: steroid receptor transactivation profile in Chinese hamster ovary cells and ovulation inhibition in rat and monkey

Background: Activity of nomegestrol acetate (NOMAC), levonorgestrel (LNG), drospirenone (DRSP), dienogest (DNG) and progesterone on human steroid receptor transactivation was investigated. Ovulation inhibition by NOMAC, LNG and progesterone was tested.

Study design: The progestogen receptor profile was determined in Chinese hamster ovary cells transfected with human progesterone B (PRB), androgen, estrogen (ER(α) and ER(β)), glucocorticoid (GR) and mineralocorticoid (MR) receptors, respectively. Ovulation inhibition was tested in rats and monkeys.

Results: Agonistic potency rankings for PRB were LNG=NOMAC≫progesterone≫DRSP>DNG. No antagonistic activity at PRB was observed. Only LNG had androgenic activity. Antiandrogenic potency rankings were LNG≫NOMAC>progesterone>DNG>DRSP. All agents were devoid of activity at ER(α), ER(β) and GR. Only progesterone, DRSP and LNG had anti-MR activity. The NOMAC dose inhibiting ovulation at 50% ranged from 0.14 mg/kg (monkey) to 1.25 to 5.0 mg/kg (rat).

Conclusion: Nomegestrol acetate is a selective progestogen and a potent inhibitor of ovulation in the rat and monkey.