Constrction of the Neonatal Aorta by Raised Oxygen Tension

Abstract

A preparation consisting of the great arteries around the heart from neonatal guinea pigs was perfused at constant flow by physiological saline solutions in a bath in which various gases (95% N₂ + 5% CO₂, air + 5% CO₂ and 95% O₂ + 5% CO₂) were bubbled. The pressure drop across the aorta, including the preductal area, was recorded and the changes in resistance in response to these gas tensions were calculated. The well-known closure of the ductus with increased P_o2 occurred, but in addition there was a reversible increase, up to 400%, in the resistance of the aortic segment. This was maximal 1 to 2 days after birth, diminishing with age until after 6 days it was very slight. In very young animals (1 to 2 days), responses to air and oxygen were roughly proportional to the P_o2. Inspection of injection casts of the vessels showed that the constriction was local in the preductal area, closely resembling that of aortic coarctation. Segments of aorta that did not include the preductal area, and from animals of comparable age, showed very slight constriction to raised P_o2. The neonatal vessels of pigs, rabbits and cats showed similar O₂ sensitivity of different degrees, and with different peculiarities as to time lag and repeatability. Neither the ductus nor the neonatal aorta of dogs appears to constrict to increased P_o2, and closure of the ductus in this species must be by a different mechanism. These observations may be interpreted as evidence for the Skodaic theory that infantile aortic coarctation may occur in association and coincident with the closure of the ductus at birth. The administration of high O₂ gases at birth might, in cases of abnormal development, lead to permanent coarctation.