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1 Institute for Biomaterials and Biomedical Engineering, 2 Departments of Obstetrics and Gynecology and 3 Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5S 1A8; 4 School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia B3H 4H7; and 5 Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5
We previously reported changes in mechanical properties and collagen cross-linking of the ovine thoracic aorta during perinatal development and postnatal maturation, and we now report changes in biochemical composition (elastin, collagen, and DNA contents per mg wet wt) over the same developmental intervals. A comparison of results from the present and previous studies has yielded novel and important observations concerning the relationship between aortic mechanics and composition during maturation. Developmental changes in aortic incremental elastic modulus at low tensile stress (Elow) closely followed changes in relative elastin content (i.e., per mg wet wt). An 89% increase in Elow during the perinatal period was associated with a 69% increase in relative elastin content, whereas neither variable changed during postnatal life. Incremental elastic modulus at high tensile stress (Ehigh) did not change during the perinatal period but increased 88% during postnatal life. This pattern closely paralleled changes in collagen cross-linking index, which did not change perinatally but almost doubled postnatally. In contrast, relative collagen content (per mg wet wt) increased only slightly from fetal to adult life, a trend that was unrelated to aortic mechanics. Substantial, progressive decreases in measures of wall viscosity (pressure wave attenuation coefficient and viscoelastic phase angle) from fetal to adult life followed the pattern observed for relative DNA (smooth muscle cell) content (per mg wet wt). Our findings suggest that accumulation of elastin per milligram wet weight contributes most to developmental changes in Elow, change in collagen cross-linking is the primary determinant of developmental changes in Ehigh, and cell accumulation contributes most to developmental changes in wall viscosity.
elasticity; viscoelasticity; development; elastin; collagen
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