Dynamic change of the vascular wall from transmural to intercellular passage of red blood cells observed in splenic regeneration.

Rat splenic tissues were autotransplanted into the major omentum, and the operated animals were treated with phenylhydrazine to investigate the passage of erythrocytes through the vascular wall during splenic regeneration. Both ways of the passage were differentiated during regeneration. From day 1 to day 5 after transplantation, the pores were formed in the endothelial cells, through which erythrocytes (chiefly reticulocytes) migrated, and were closed by the basal lamina when erythrocytes did not penetrate. From day 7 to day 10, endothelial cells proliferated, and some of them were transformed into sinus endothelial cells containing condensed microfilaments and formed the interendothelial slit, but few erythrocytes passed there at this stage yet. On and after day 11, when the sinus endothelial cells exhibited well-developed microfilaments, reticular cells contained moderately developed microfilaments and the basal lamina developed well, the slits were opened, where a large number of erythrocytes passed. These results showed, concerning the passage of blood cells, that the vascular wall in the splenic autografts changed from the transmural pattern to the intercellular one after a marked proliferation of endothelial cells and that the effective passage of erythrocytes was closely associated with the development of microfilaments in the cytoplasm of endothelial cells and basal lamina as well as the interaction of reticular cells.