Unnatural substrate

In addition, another limitation is that in vitro endothelial cells may behave differently under still vs. flowing culture conditions and with attachment to different matrices. Thus, although in vitro assays are rapid, readily quantifiable and consistently reproducible, they do not permit study of the complex physiological interactions that occur in vivo. Furthermore, the assessment of indirect effects of a compound (exerted on nonendothelial cells that in turn produce compounds that then act on endothelial cells) are difficult to reproduce. Therefore, wherever possible, in vitro assays should be carried out using endothelial cells from more than one source, or more importantly, be followed up with one or more in vivo assay of angiogenesis.