Sprouting angiogenesis - the growth of new blood vessels from a preexisting vasculature - can be triggered by cells in hypoxia in order to re-stablish the oxygen and nutrients supply to the tissue.
The formation of a new vessel is a multistep process starting by the activation of the Endothelial Tip Cell (ETC) phenotype that migrates through the tissue guided by chemotactic cues, such as the Vascular Endothelial Growth Factor (VEGF) concentration. The cells near to the ETC gain the Endothelial Stalk Cell (ESC) phenotype and start to follow the ETC and proliferate in order to form the new branch.
The Endothelial Cells (ECs) re-arrange in the new branch, forming the lumen. Thus Smooth Muscle Cells (SMC) and pericytes are recruited to maturate the new vessel. Consequently the vessel is filled with blood from the main branch.
My question is: when does the new vessel starts to deliver oxygen to the surrounding tissue? Can it occurs before the anastomosis formation where the circulation is stablished, even for a short period of time due to the plasma that filled the new branch? (See the following picture where they represent the cells near to the new branch with a high concentration of oxygen even without anastomosis/blood circulation)
Image Source: Peter Fraisl et al. Regulation of Angiogenesis by Oxygen and Metabolism. DOI 10.1016/j.devcel.2009.01.003