Changes in the mechanical properties and residual strain of elastic tissue in the developing fetal aorta.

Formed almost exclusively during development, arterial elastic fibers must function for the lifetime of the animal. We have observed dramatic structural and mechanical changes in aortic elastic tissue during gestational and postnatal development. Elastic tissue was isolated from bovine aortas: (i) during late pregnancy and (ii) in adults. Changes in the relative content of aortic elastic tissue were assessed, as were the viscoelastic properties and residual strains of purified aortic elastic tissue rings. As aortic elastic tissue content increased during development, its circumference and thickness increased-but with circumference rising faster than wall thickness, causing a relative thinning of the elastic tissue. At the same time, elastic tissue stiffness increased while viscoelastic behavior decreased. Much of these changes were concentrated during late gestational development, such that the changes observed during the short span of late gestation examined (~60 days) were similar in magnitude to those occurring over the much longer postnatal period (approximately 1-2 years). Finally, we observed an approximately threefold increase in residual strain in aortic elastic tissue from fetal to adult life, with most of this increase again occurring in late gestation. These results suggest that rapid remodeling, as well as accumulation, of aortic elastic tissue occurs during late gestation. These changes significantly alter both fetal aortic mechanical properties and residual stresses.