Some structural and functional aspects of endothelial cells.

Contrary to our former belief, endothelial cells can no longer be classified as a homogeneous cell population which, as a living border layer between the blood and the extravascular space, serves exclusively as a selective filter. The technique of routinely culturing endothelial cells from various sources has provided new insights into an unexpected multitude of synthetic and metabolic capacities of these cells, such as the degradation of arachidonic acid, the enzymatic activation of angiotensin I, and many others. However, many of these results are still contradictory, and therefore make any critical review of the data almost impossible. Some examples for this are briefly outlined in this contribution. Irrespective of this, these new results have to be taken into account, although the possibly high specificity of the endothelium will render the interpretation of future data, particularly those obtained from animal models, much more difficult. However, a simple neglect of these complexities would be disastrous for all future endothelial research.