Progestational agents prevent preterm birth induced by a nitric oxide synthesis inhibitor in the mouse

Background: The ability of the nitric oxide (NO) synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) to induce preterm parturition in the mouse has been previously documented. The present study tested the ability of progestational agents to prevent preterm birth induced by L-NAME. Materials and Methods: L-NAME was administered subcutaneously at 90 mg/kg on gestation day 16. Progesterone, medroxyprogesterone acetate and hydroxyprogesterone caproate were administered subcutaneously at 0 (vehicle), 5 or 10 mg/kg on gestation day 16 one hour before L-NAME and on day 17. Parturition was considered preterm if occurring before gestation day 18. Results: Following treatment with L-NAME alone, 56.5% of the pregnant animals delivered before term. Treatment with progesterone, medroxyprogesterone acetate or hydroxyprogesterone caproate at 5 mg/kg or 10 mg/kg significantly and comparably reduced the rate of preterm birth caused by L-NAME. Conclusion: Progestational agents are able to reduce preterm births induced by nitric oxide synthase (NOS) inhibition.