Effect of Oxygen and Umbilical Cord Clamping on Closure of the Ductus Arteriosus in the Guinea‐Pig and the Rat. Studies on Closure of the Ductus Arteriosus. VI

Abstract

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.

Oxygen increases ductus arteriosus smooth muscle cytosolic calcium via release of calcium from inositol triphosphate-sensitive stores

“…An acute increase in oxygen tension causes perinatal pulmonary vasodilation (3,26), even while it results in constriction of the DA (1,5). Initial closure of the DA in response to an increase in PO 2 is caused by vessel constriction (14), whereas long-term closure is accomplished through cell migration, apoptosis (25), and cell proliferation (4,15,18).…”

Studies on Closure of the Ductus arteriosus

“…Since ductal constriction can be elicited by the ad ministration of catecholamines or acetylcholine both in vivo and in vitro, it was considered of interest to analyze the role of autonomic transmitters in this phenomenon. Mature adrenergic terminals are abundant through out the wall of the human fetal ductus, as recently demonstrated with the Falck-Hillarp histochemical method [3], In the present study the wholebody freezing technique [5,7] was used since earlier studies had shown that this technique is sensitive enough to demonstrate that decrease in body temperature [8] and in oxygen saturation [6] delays the closure rate.…”