[Postnatal changes in the ductus arteriosus and brown adipose tissue: a review and an exploratory post-mortem study...

After a short review of the literature, postnatal changes in the ductus arteriosus Botalli are described in 52 lambs sampled in 1970 and 1971. Five groups of animals were formed on the basis of findings. (I) All lambs (n = 18) that died of asphyxia or prematurity had open ducti and, in most cases, severe adventitial bleeding (2). Completely anatomically closed ducti were found in I-week-old lambs (n = 9). Lambs that died within about 4 days of birth were grouped as (3) low-birth weight (dysmaturity) (n = 2), (4) normal weight and died after bacterial infection (n = 7), or (5) normal birth weight and died of other causes (n = 6). The dysmature lambs died because of cold and poor suckling. Compared with the lambs with a normal body weight, the dysmature lambs had almost completely closed ducti. Extensive, often circular, haemorrhages at the periphery of the necrotic muscular tissue of the ductal media were found in the dysmature and infected lambs. In these lambs, the brown adipose tissue surrounding the ductus was red-brownish and often depleted of its fat. This fat depletion and haemorrhages were less severe in lambs that died of other causes. The haemorrhages in the media of the ductus arteriosus, which were not found in older lambs, have not been described previously in other species, including humans. These haemorrhages are most likely the result of a short period of ductal relaxation, resulting in the passage of blood through the vasa vasorum and leakage of blood cells from degenerated capillaries at the border of the necrotic muscular tissue. It is hypothesized that the relaxation results from one or a combination of the following: (i) direct heat from heat-producing brown adipose tissue surrounding the ductus (because of cold or infection), (2) infection or inflammatory mediators, and (3) adipose tissue-derived relaxing factors.