Development of capillary networks from rat microvascular fragments in vitro: the role of myofibroblastic cells.

A new model useful for studying capillary growth in vitro is described. When the microvessel fragments and accompanying single cells (myofibroblastic cells) from rat epididymal fat pads were co-cultivated, the myofibroblastic cells initially began to grow and reached confluence. A few days later, endothelial cells started to sprout from the vessel fragments, forming cellular cord networks on and in the multilayered myofibroblastic cells. Ultrastructurally, the lumina, surrounded by the endothelial cells having intercellular junctions, were observed at cross-sectioned cellular cords. The growth of cellular cords from the fragments always occurred after the myofibroblastic cells had reached confluence. The medium conditioned to isolated rat myofibroblastic cells stimulated not only the proliferation of the endothelial cells from the bovine capillary and human vein but also the migration of bovine capillary endothelial cells in vitro. Moreover, the extracellular matrix produced by rat myofibroblastic cells modulated the morphology of bovine capillary endothelial cells to a cordlike shape. These observations strongly suggest that the formation of the capillary in vitro is induced by myofibroblastic cells.