Closure of the ductus venosus. The ductus venosus, which carries portal and umbilical blood to the inferior vena cava, is functionally closed within hours of birth. Permanent closure begins a few days after birth and is complete by 18-20 days of age . The duct becomes the ligamentum venosum in a fissure on the back of the liver.
Comparative Species Closure of the foramen ovale. In the rat, the foramen ovale is diminished in the first two days after birth and is completely closed three days after birth (Momma et al., 1992a).
Closure of the ductus arteriosus. In the rat and mouse, functional closure of the ductus arteriosus is complete by 2-5 hr after birth . Functional closure is complete in a few minutes after birth in guinea pigs and rabbits . In rats, rabbits, guinea pigs and lambs, anatomical closure is complete in 1-5 days after birth . In dogs, anatomical closure of the ductus arteriosus occurs at about 7-8 days after birth (House and Enderstrom, 1968).
As in the human infant, the biochemistry behind the initial functional closure of the ductus arteriosus is believed to involve a balance between the opposing actions of oxygen and PGE 2 . Studies in guinea pigs and lambs suggest that this contractile response to oxygen is the results of interaction between oxygen and a cytochrome P 450 -catalyzed enzymatic process, that can be inhibited by carbon monoxide . Specifically, cytochrome a 3 becomes oxidized with subsequent generation of adenosine triphosphate (ATP) and muscle cell contraction. In full-term animals, the loss of responsiveness to PGE 2 shortly after birth prevents the duct from reopening once it has constricted (Clyman, et al., 1985a). This change in responsiveness may involve the presence of thyroid hormones (Clyman, et al., 1985b).