Ultramicroscopic three-dimensional investigation of the initial steps of intussusceptive angiogenesis during glomerulogenesis in the porcine embryonic kidney. The morphological features are combined with the immunohistochemical detection and cellular localization (through immunogold labeling and transmission electron microscopy) of both angiopoietins 1&2, their receptor TIE2 as well as TIE1 to reveil the fnctional role of these molecules in intussesceptive angioensis.