EFFECT OF OXYGEN AND UMBILICAL CORD CLAMPING ON CLOSURE OF DUCTUS ARTERIOSUS IN GUINEA-PIG AND RAT. STUDIES ON CLOSURE OF DUCTUS ARTERIOSUS .6.

Full‐term guinea‐pigs were delivered by caesarean section. Living fetuses with intact, or interrupted umbilical circulation were allowed to breathe, for periods of 5 min, air or nitrogen, or air followed by nitrogen. Animals sacrificed immediately on birth served as controls. Sacrifice was performed in liquid nitrogen.–Spontaneously delivered rats were either sacrificed immediately on birth or kept up to 4 hrs at 37° C in air or 8 c/c O2 in N2, before sacrifice in isopentane. cooled by dry ice. In addition, the heart rate of newborn rats, kept at the same temperature and in the same atmospheres, was recorded. – Changes in ductal inner diameter and wall thickness were measured in cryostat sections of both species. Oxygen caused marked constriction of the ductus in the guinea‐pig. Further constriction was found in animals with a clamped umbilical cord. No evidence was obtained of an effect of nitrogen inhalation, neither on the open nor on the constricted ductus. In the rat, reduced atmospheric oxygen concentration caused a delay in ductal closure rate. Lowering of the heart rate was also observed. The present results–obtained in vivo in the guinea‐pig and rat–show that oxygen is essential for closure of the ductus arteriosus, independent of the rate of its closure. © 1969 Scandinavian Physiological Society