AngelT
Forum Senior
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Posts: 111
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"The DA constricts at birth, but there is often a small shunt of blood from the aorta to the left pulmonary artery for a few days in a healthy, full-term infant.
In premature infants and in those with persistent hypoxia the DA may remain open for much longer.
Oxygen is the most important factor in controlling closure of the DA in full-term infants. Closure of the DA appears to be mediated by bradykinin, a substance released by the lungs upon initial inflation.
Bradykinin has potent contractile effects on smooth muscle. Action depends upon the high oxygen content of the aortic blood resulting from aeration of the lungs at birth.
When the PO2 of blood passing through the DA reaches about 50 mm Hg, the wall of the DA constricts. (May be mediated direct or may be mediated by Oxygenís effect on decreasing PG E2 and prostacylcin secretion. (unlike in a coarctation of aorta which requires PGE2 infusion to reopen the DA for blood flow.
As a result of reduced pulmonary vascular resistance, the pulmonary arterial pressure falls below the systemic level and the blood flow thru the ductus arteriosis is diminished"
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