(a and b) Aortic diameter changes after NaCl and CaCl₂ treatment in C57BL/6 and MMP-2KO mice (a), and in 129/SvEv and MMP-9KO mice (b). Aortic diameters were measured before NaCl or CaCl₂ incubation (white bars) and at sacrifice (gray bars). Bars shown in each group represent the mean ± SE of 5–14 mice. The diameter in the CaCl₂-treated group was increased significantly at sacrifice in C57BL/6 and 129/SvEv mice (*P < 0.01). (c–m) Histologic changes of mouse aorta at 10 weeks after treatment. (c–f) Trichrome staining for elastic fibers. NaCl-treated (c) and CaCl₂-treated (d) aorta from C57BL/6 and NaCl-treated (e) or CaCl₂-treated (f) aorta from MMP-2KO mice. (g–j) Pentachrome staining for elastic fibers. NaCl-treated (g) and CaCl₂-treated (h) aorta from 129/SvEv and NaCl-treated (i) or CaCl₂-treated (j) aorta from MMP-9KO mice. (k–m) Immunoperoxidase staining for macrophages of mouse aorta 2 weeks after CaCl₂ incubation in 129/SvEv (k), MMP-9KO (l), and MMP-2KO (m). Mac3-positive cells are indicated by arrows. Elastic fibers are represented by arrowheads. (×100).