Distribution of alkaline phosphatase in the microcirculatory pathways of the coronary system.

By histochemistry alkaline-phosphatase-activity in the microcirculatory pathways of the coronary vascular system were investigated. In the capillary network paralleling the myocardial fibers enzyme activity was found positive whereas in the large sinusoidal, endothelial vessels, linking transmurally neighbouring capillaries, there was no alkaline phosphatase activity. In both endothelial cell types, in capillaries and in sinusoids, a transendothelial vesicular thorotrast transport could be shown. It is supposed that the sinusoidal vessels preponderantly have to cope with intercapillary shear stress. Their nutritial function is believed to be of less importance. At least the lack of alkaline phosphatase activity should indicate that there is no selective transendothelial transport in the wall of these sinusoids.