Blood vessels of the common tree shrew (Tupaia glis) were embedded in Araldite, sectioned at 0.5-1 microm thickness, and observed with light microscope (LM). It was found that the vascular wall could be classified into three categories: (1) those with proper vasa vasorum (PVV); (2) those with collaborative vasa vasorum in perimural tissues; (3) those without vasa vasorum. The PVV were located in the the tunica media, between the tunica media and the tunica adventitia, and in the tunica adventitia of the vascular wall. On studying the vascular casts with a scanning electron microscope (SEM), it was noted that what appeared to be vasa vasorum did not always conform to those found under the LM. Furthermore, the PVV seen in a particular blood vessel among different tree shrews were not always related to intraluminal partial pressure of oxygen, vascular size, and thickness of the wall. In contrast, the results of this study indicate that the activeness of the vascular wall in varying the amount of blood flow to certain organs is an important factor that is associated with the existence, density, and distribution of the vasa vasorum.
Copyright 2005 Wiley-Liss, Inc.