Proliferation of smooth muscle cells at sites distant from vascular injury.

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Abstract
This study investigated the phenomenon that injury at one specific site in blood vessels induces cell replication at distant vascular sites. A polyethylene tube was inserted via the common carotid into rat aortic arch, which caused focal endothelial cell loss and formation of platelet thrombi. In a similar fashion, a polyethylene tube was placed into the lower abdominal aorta via a femoral artery. All animals received 3H-thymidine continuously for 2 weeks, after which time segments of the aorta distant from the polyethylene tubing were processed for autoradiography. These sites showed no loss of endothelium or adherent platelets, and yet the smooth muscle and endothelial cell replications were significantly elevated as compared to control aortas. There was no significant change in blood pressure during these experiments and no increase in smooth muscle cell ploidy. When the polyethylene tubing was left in situ for 2 months, no increased replication of the smooth muscle cells was observed during the last 2 weeks of the experiment, and at this time the aorta adjacent to the tubing was completely re-endothelialized. Finally, the mitogenic activity of plasma from these animals was tested in vitro. At the time of a significant increase of in vivo cell replication (2 weeks), the mitogenic activity of the plasma from animals with the indwelling tubing was similar to that of the control animals. In summary, these data show that injury at one discrete arterial site leads to general cell proliferation in the same vessel, and the data would support the possibility that cell communication initiates this response.

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