ROLE OF MESENCHYMAL CELLS IN THE NEOVASCULARIZATION OF THE RABBIT PHALLUS

The neovascularization of the rabbit phallus at ages between prenatal days 15 and 21 was investigated by light- and electron microscopy, com puter-aided light microscopic reconstruction, and immunocytochemistry. The phalli are embedded by an abundance of mesenchymal cells, which a re in contact with the neighboring ones or with the endothelial lining of growing capillaries. They often form solid cell cords that eventua lly make contact with the growing capillaries. The computer-aided reco nstruction of the serial light micrographs reveals that these cell cor ds are involved in connecting the adjacent capillaries. The incorporat ion of such mesenchymal cell projections into the endothelial lining, occasionally conjugated with simple attachment devices, is frequently observed by transmission and scanning electron microscopy. The contact areas between the mesenchymal and endothelial cells show immunoreacti ons of fibronectin. These results indicate the successive transformati on of mesenchymal cells to endothelial cells of the growing capillarie s. As endothelial cells of the growing capillaries show mitotic prolif eration, such vasoformative mesenchymal cells seem to be involved in t he acceleration of the neocapillarization of the rabbit phallus. Fibro nectin actively produced in the mesenchymal cells may participate in t heir migration and the mechanical linkage with the endothelial cells. (C) 1994 Wiley-Liss, Inc.