Ultrastructural and immunohistochemical analysis has shown that pericytes contain myofilaments, although less than vSMC.In vivo, it has been difficult to determine whether the observed microvascular contraction was due to endothelial cell or Vilazodone pericyte contraction, or both.To what extent pericyte contractility contributes to physiological regulation of capillary blood flow remains unclear.The pericyte coverage of the abluminal endothelial surface is only partial, and varies extensively between the capillary beds of different tissues. The reason coverage is as low as in some tissues and as high as in other tissues is not known, but likely reflects specific functional features of the microvessels in different organs.In addition, the distribution of pericytes in the vessel wall of any specific capillary bed is not random.Pericytes are, for example, more prevalent at capillary branch points, although their occurrence at this site is not obligatory. Typically, the part of a vessel engaged in the transport of gases andor nutrients is free of pericyte coverage, as is seen, for example, in the capillaries of the choroid and in the skin, where pericytes lie on the distal side of the vessel relative to the retinal cells and keratinocytes, the assumed principal target cells for the gasnutrient delivery at these sites.The positions of pericytes are also polarized relative to surfaces of respiration. Left reveals the main cellular pericytic process, which is intimately associated with the endothelium. Arrow infpoints to a pericyte nucleus engulfed by desmin staining.This is true even for the pericytes that accompany the migrating endothelial tips in the retina NG represents an excellent surface marker that allows visualization of the entire extension of pericytes on the endothelial plexus.Although the reason for this is unclear, it may well relate to the exceptionally high metabolic activity and therefore the requirement of a meticulously regulated blood flow in the retinal capillaries.Whether pericytes also influence the bloodbrain barrier at the level of the endothelial tight junctions and transendothelial vesiculation is presently not clear.The difficulties that we face in trying to determine a general function of pericytes may at least in part reflect the Stugeron variety of specializations of blood vessels in different organs, which relates to the organ metabolic demand and to specialized vascular functions, such as infiltration, excretion, and gas exchange.It is possible that no such general pericyte function exists, but that pericytes have largely distinct functions in different vascular beds.For example, in chicken embryos, pericytes surrounding the angiogenic vasculature of the brain can easily be identified by their expression of SMA. In mature vessels, the most reliable identification is still electron microscopy, revealing the complete surrounding of the pericytes by the endothelial basement membrane.However, in embryogenesis and during angiogenic sprouting this method of identification cannot be applied, since the basement membrane is not fully developed.When addressing the involvement of pericytes in angiogenesis, we must therefore keep in mind that unambiguous positive identification of pericytes is still a problem.Furthermore, transdifferentiation from endothelial cells may partially contribute to the vSMC population in the aorta. Endothelial cells are thought to derive from angioblastsgiving rise only to endotheliumor from hemangioblastwhich are precursors of both endothelial cells and blood cells.