Elastic lamina growth in the developing mouse aorta.

The growth and development of elastic laminae in the mouse aortic media were investigated by light and electron microscopic autoradiography after a single SC injection of L-[3,4-3H]-valine. Because of the remarkable stability of elastin, radiolabel incorporated into the elastic laminae during early stages of aortic development can be identified in the mature vessel. Light microscopic autoradiographs of aortae from mice injected with radiolabeled valine at 3, 14, or 21 days of postnatal age and sacrificed at 4 months of age showed silver grains evenly distributed around the circumference of the vessel, suggesting uniform elastic lamina growth. Electron microscopic autoradiographs of aortae from mice injected at 3 and 14 days' postnatal age and killed at 4 months of age showed the elastin initially deposited at 3 days to be in the center of the lamina, whereas the elastin deposited at 14 days remained peripherally located. These observations suggest that elastin deposited early in development does not undergo any significant redistribution during growth of the vessel. Because the aorta continues to increase in diameter after the elastic laminae are essentially complete, the fenestrations in the laminae were investigated as possible sites of further expansion of the laminae. In aortae from mice injected at 3 days and sacrificed at 4 days of postnatal age, the edges of the elastic lamina that border on fenestrations showed a large number of silver grains. Regions of the elastic lamina at some distance from the fenestration, however, appeared to be associated with fewer grains. Results from this study not only present unique observations of elastin deposition in developing elastic laminae but also provide evidence that the fenestrations in the elastic laminae may play a role in their continued expansion during later stages of aortic development.