Our aim is to measure circulating endothelium cells in blood of rat. In the begining we need a reliable positive control: to remove by some manipulation the alive endothelial cells from blood vessel. Thanks in advance!
If I understand your question correctly, you want to isolate endothelial cells from a blood vessel. I would suggest you use the basic protocol for isolation of human umbilical vein endothelial cells (HUVECs) from an umbilical cord as a starting point. A good example is found here:
Larger vessels can be tied-off with dental floss, everted (turned inside-out) over the tip of a hemostat, and suspended in a solution of collagenase to remove the endothelial cells. I suppose smaller vessels could be simply tied-off and filled with the enzyme solution. See: http://www.ncbi.nlm.nih.gov/pubmed/7287826
It depend on from where you want to isolate the cells.
Larger blood vessels, it easy to isolate as mentioned by Ruben Bierings and Don Kaiser.
Smaller vessels bit complicated. you can use capillary slice in growth medium. Endothelial cells protrude out of the slice, which can be further subcultured