On the regeneration of aortic endothelium at different ages.

In order to study the physiological regeneration of the endothelium, "Hautchen", preparations of aortic endothelium were produced from 15 rabbits of different ages and studied autoradiographically. By determining the number of 3H-thymidine-labelled cells, the mitotic rate and the total number of cells per 0.12 mm2, we arrived at the following conclusions: (1) The mean generation time of endothelial cells increases with advancing age. The extension of the mean generation time of the endothelial cells, as deduced from the decrease in the 3H-thymidine labelling index and in the mitotic rate, mainly occurs during the first four months of life. (2) Neither between topologically different aortic segments nor between such portions of the aorta as are exposed to different flow-mechanical stresses could any considerable differences with regard to the reproduction rate of their endothelial cells be detected. The raised endothelial turnover in the area of the iliac bifurcation requires further studies.