Developmental remodeling of the internal elastic lamina of rabbit arteries: effect of blood flow.

We examined remodeling of the internal elastic lamina (IEL) of rabbit arteries from 3 to 23 weeks of age. The IELs were fenestrated at all ages; however, the sizes of the fenestrae increased dramatically during postnatal development. Mean areas occupied by the individual fenestrae of the carotid artery IEL increased from 11.3 +/- 0.7 microns2 in 3-week-old rabbits to 61.2 +/- 5.5 microns2 in adult rabbits. The estimated number of fenestrae per vessel also increased greatly, from 2.68 x 10(5) to 9.27 x 10(5); however, the increased number of fenestrae did not keep pace with growth of the artery, since fenestrae per square millimeter decreased by 26%. Large increases in the size of fenestrae were also observed in the renal and iliac arteries, although greater decreases in fenestrae per square millimeter occurred with age (70% in iliac arteries). Morphological assessments suggested that enlarging fenestrae frequently fuse with neighbors. By contrast with other arteries, the IEL of the abdominal aorta was not a continuous fenestrated sheet in young animals, perhaps reflecting the extensive remodeling that this vessel undergoes in the postnatal period. We decreased common carotid blood flow by 70% in 5 rabbits at 10 weeks of age by ligating the ipsilateral external carotid artery, and we approximately doubled blood flow in 5 others at the same age, by contralateral common carotid ligation. At 15 weeks of age, fenestrae in the artery carrying increased flow were 39% larger than fenestrae in the control artery, whereas fenestrae were 53.5% smaller after 70% decreases in flow (P < .05). We conclude that flow-dependent enlargement of fenestrae contributes to developmental remodeling of the IEL. Remodeling of the IEL may also have important implications for transport of materials and cell-cell communication between the intima and media.