Endothelium Function Is Protected by Albumin and Flow-Induced Constriction Is Independent of Endothelium and Tone in Isolated Rabbit Femoral Artery

To investigate the preservation of endothelial function, we perfused two segments of one rabbit femoral artery (n = 8) in a pressure myograph in parallel, both with Tyrode, but one with 0.6% albumin added. The change in the outer diameter of the vessels [preconstricted with norepinephrine (NE) to 70%] in response to acetylcholine as an indicator of the endothelial function, was repeatedly measured over 5 h after the equilibration. The difference between the acetylcholine responses of the two vessel segments was significant (p < 0.05) after a perfusion period of 4 h. We also investigated whether flow-induced constriction is dependent on (1) the presence of endothelium and (2) the level of preconstriction. We therefore perfused segments of rabbit femoral arteries (n = 5) with Tyrode with 0.6% albumin. If acetylcholine-induced dilatation was present, a flow-diameter relation was determined at two constriction levels: about 60% (high) and 90% (low) of the passive outer diameter. Both determinations were repeated after mechanical endothelium removal (checked functionally and histologically). A similar decrease in diameter (about 7%) with an increase in flow ranging from 0 to 1,330 microliters/min was found in all conditions. We conclude that the addition of (0.6%) albumin protects endothelial function in the rabbit femoral artery when perfused in the low-flow range for a period longer than 4 h. We also found that flow-dependent constriction is neither influenced by the presence of the endothelium nor by the level of tone induced with NE.