EMBRYOLOGICAL OBSERVATIONS OF DUCTUS ARTERIOSUS IN GUINEA-PIG, RABBIT, RAT AND MOUSE. STUDIES ON CLOSURE OF DUCTUS ARTERIOSUS .4.

Fetuses of guinea‐pigs, rabbits, rats and mice were obtained by caesarean section in late pregnancy. They were immediately sacrificed, and fixed by whole‐body freezing, after which transverse cryostat sections of the ductus arteriosus were prepared for morphological observations. The inner diameter and wall thickness of the ductus were measured at its narrowest part. The descending thoracic aorta of full‐term rat fetuses was treated in the same way as the ductus. In all species, the mean inner diameter of the ductus increased with fetal age, and was accompanied in the guinea‐pig and rabbit by a gain in thickness of the media. The development of an intima was most evident in rabbit fetuses. In all species, the structure of the ductal wall was comparable in the youngest and oldest fetuses. The inner diameter and wall thickness of rat and mouse fetuses near term corresponded well to values in newborns. The divergent values between fetuses and newborns of the guinea‐pig and rabbit are discussed. The relation recorded between the cross‐sectional areas of the ductus arteriosus and thoracic aorta is in agreement with the present concepts of prenatal circulation. The similarities in ductal morphology between full‐term fetuses and newborns might justify the use of full‐term fetuses in experiments on the physiology of the ductus arteriosus. © 1969 Scandinavian Physiological Society