Fine structure of capillary proliferation in myocardium of volume overloaded rats.

We studied the fine structure of capillary endothelial cells of volume over-loaded cardiac hypertrophy in rats using A-V shunt between the left common carotid artery and the left external jugular vein. The duration of experiment was 1, 2 and 4 weeks. Volume overload of the heart was constantly induced, because blood flow index (ml/min/kg) of both carotid arteries was increased throughout the experiment and the volume and the weight of the left ventricle were significantly increased in 2 and 4 weeks. After the making of the large panorama photograph composed of 24 TEM photographs, the number of the endothelial cells of each capillary was directly counted under TEM. In 2-week shunted animals, incidences of over 3 endothelial cells per capillary were definitely increased. Also bulging of the endothelial cells, overlapping of two endothelial cells and increasing of microvilli on the luminal surface were mostly prominent in 2 weeks. Endothelial cells of intramyocardial capillaries are considered to be activated as early as 1 week and proliferated in around 2 weeks after volume-overload. An increase of coronary blood flow might be one of the most important causes of the endothelial proliferation and regulated by dilatation of the capillary lumen.