Ultrastructural and cytochemical study of microvascular enzyme activity in experimental brain tumors of rat.

We studied the fine structure and ultracytochemical features of microvessels of both normal rat cerebrum and brain tumors transplanted into rats. Ultrastructurally, the endothelial cells of the tumor vessels showed alterations, compared to those of normal vessels, such as attenuation, thickening, and/ or abnormal endothelial junctions. In the control rats, an ultracytochemical study revealed alkaline phosphatase (AlPase) and adenosine triphosphatase (ATPase) activities were located mainly on the luminal plasma membrane of the endothelial cells, and 5'-nucleotidase (5'-N) activity on the abluminal plasma membrane. In the transplanted brain tumors, the sites of AlPase and 5'-N activities were similar to those of the controls, but the extent of the reactions on the abluminal and luminal mem branes of the endothelial cells was greater. ATPase activity occurred mainly on the luminal plasma membrane of the endothelial cells in the controls, and on the abluminal membrane in the transplanted brain tumors. The number of pinocytotic vesicles showing positive reactions for AlPase, 5'-N, and AT Pase was not higher in the tumor vessels than in the normal vessels. The redistribution of membrane enzymes in the endothelial cells of the transplanted brain tumors is presumed to be related at least part ly to the changes in the endothelial junction.