Rapid accumulation of elastin and collagen in the aortas of sheep in the immediate perinatal period.

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Abstract
While characterizing developmental changes in aortic wall composition in sheep, we observed very rapid accumulation of elastin and collagen in the immediate perinatal period. Thoracic aortic elastin content increased by 41%, and collagen content increased by 49% in approximately 1 week, between 140 days gestation and 3 days postpartum (term = 145 days). Even larger changes were observed in the abdominal aorta. Elastin content increased by 66%, and collagen increased by 57%. The pronounced increase in wall tissue accumulation near birth preceded a marked postnatal increase in arterial pressure. We propose that this elastin and collagen accumulation is a preadaptive response in preparation for the later increase in pressure. The prenatal and postnatal events that initiate this synthesis and accumulation are not known. We also found that, in the 3 weeks after this initial rapid increase, accumulation of elastin and collagen was markedly reduced in the abdominal, but not the thoracic, aorta. This latter finding may be linked to the dramatic decrease in flow through this vessel that results from the loss of the placental circulation. Finally, we observed that relatively high smooth muscle cell replication rates in the abdominal aorta postpartum resulted in no net DNA accumulation. This finding indicates that cell turnover plays an important role in postnatal arterial growth and development.