血流量(ずり応力)負荷による動脈内弾性板の変化について

抄録

Various morphological changes have been reported in the blood flow loaded canine carotid arteries by Masuda et al. Acute blood flow load for about one week induced changes in the endothelial cells and in the subendothelial layer. On the other hand, chronic blood flow load induced the structural changes in the deeper layer of the arterial wall, such as the increase of the internal radius and the increase of the elastic fiber in the media. In the present experiments, we focused on the internal elastic lamina (TEL) in the flow loaded artery. Experiments : To induce blood flow change, arterio-venous anastomosis was constructed between the right common carotid artery and the right external jugular vein in 27 adult female beagle dogs. Left common carotid artery was sutured with left external jugular vein in their adventitias and used for sham-operated control. Three dogs were used for non-operative control. Animals were kept for 1 week, 4 weeks and 6 to 9 months. The blood flow ratio (BFR) of the right (shunted) common carotid artery to the left (control) common carotid artery at the final measurement before sacrifice and the blood flow increase ratio (BFIR) of the same artery (blood flow rate at the final measurement/blood flow rate before anastomosis) were used for the indexes of the blood flow loadance. After the final measurement, artery was normotensively fixed (about 100 mmHg) with 3% glutaraldehyde solution and observed histologically and with electron microscope, especially using special stain (tannic acid uranyl acetate) for elastic fiber. Results: In the blood flow loaded shunted arteries (BFR<1.5, BFIR<3.0), small sized longitudinal elastic fibers appeared in the abluminal side of the TEL in 1 week. Duplication and/or multiplication and splitting of the TEL were observed in 4 weeks. The duplication and/or multiplication and the splitting of the IEL was less frequent in 6 to 9 months than those in 4 weeks. Discussion: Kamiya and Togawa showed that the shear stress dependent adaptive dilatation of the canine carotid artery in the same arterio-venous shunted system as this experiments. It is suggested that the changes of the TEL are dependent on the wall shear stress loadance, because wall shear stress is high in 1 to 4 weeks and may be reduced to the control level in 6 to 9 months.