Cytoplasmic contractile apparatus in aortic endothelial cells of hypertensive rats.

Hypertension was produced in male Wistar rats (150 gm. body weight) by complete ligature of the aorta between the renal arteries. Electron microscopic examination revealed that 1 week later the amount of cytoplasmic microfilaments in the endothelial cells of the aortic segment above the coarctation (mean blood pressure 160 mm. Hg) was strikingly increased as compared with normal animals. The endothelial cells in the segment below the coarctation (mean blood pressure 25 mm. Hg) contained few filaments and were similar to the cells in the aortic endothelium in controls (mean blood pressure 105 mm. Hg). Microfilaments measured 40 to 70 angstrom in diameter and were mostly located close to the endothelial clefts, where they formed longitudinal bundles or a network. The bundles of microfilaments contained electron-dense areas similar to the "attachment sites" of the underlying smooth muscle. By using en face preparations of aortic endothelial cells treated with antiactin autoantibodies (AAA) followed by anti-human IgG, it was seen that in hypertensive animals the cells above the ligature were intensely fluorescent when compared with those of the aortic portion below the ligature or those of the controls. The fluorescence was abolished after incubation of the AAA sera with thrombosthenin A. The correlation between electron microscopic and immunologic findings suggests that the microfilaments present in the endothelial cells of hypertensive animals are composed, at least in part, of actin. Endothelial cells so modified may play a role in permeability or may be related to other phenomena such as electrotonic coupling and synchronized contraction of aortic cells during hypertension.