ABSTRACT
Normally, at birth, after the first breath, the ductus arteriosus conveys arterial blood from the aortic arch to the pulmonary trunk (high to low pressure areas). The smooth muscle cells in the ductal wall nor mally respond to this new high oxygen tension of arteri al blood by a sustained contraction. Prostaglandins are also involved in spasm of the ductus, which is gradually transformed by fibrosis in the first weeks of infancy into the ligamentum arteriosum, thus abolishing the fetal L -► R shunt.
