Histological and ultrastructural observations of the thoracic descending aortae of wild-type (WT) and type III phosphate transporter transgenic (TG) rats. There were three rats in each group. Representative figures are shown. Hematoxylin–eosin staining of the tunica media of the descending aorta in WT rats (A) and in Pit-1 TG rats (B). There appears to be some fissures in the elastic fibers (ef) of the tunica media in the TG aorta (see arrow in inset, B) compared with the WT counterparts (A). van Gieson staining shows the presence of small tears in the elastic fibers of the TG tunica media (D), but not in the WT elastic fibers (C). The arrows indicate tears in an elastic fiber in the inset of D, while WT elastic fibers show even van Gieson staining (inset of C). Transmission electron microscopy images of arterial smooth muscle cells (ASMCs) and elastic fibers (ef) in the tunica media of WT (E) and TG (F) rats. When observed at a higher magnification, the WT elastic fibers show uniform electron density (G), while the TG elastic fibers contain fine fissures (arrows, H). Bars, A–D: 10 μm; E, F: 2 μm; G, H: 1 μm.