Ductus aeriosus closure- Functionally-immediately after bih Structurally-1-3 months after bih The ductus aeriosus functionally closes immediatly (1-2 hours) after bih smooth muscle contraction of the tunica media. Before bih, the patency of the ductus aeriosus is controlled by the low oxygen content of the blood flowing through it, which in turn stimulates production of prostaglandins, which cause smooth muscle to relax. After bih, the high oxygen content of the blood due to lung ventilation inhibits production of prostaglandins, causing smooth muscle contraction. Premature infants can be treated with prostaglandin synthesis inhibitors (such as indomethacin) to promote closure of the ductus aeriosus.