Degeneration and phagocytosis of smooth muscle cells in the neonatal rat ureter.

It was shown by ultrastructural investigation that, during the early stages of postnatal development of the rat ureter, some of the cells of the muscle coat undergo degeneration. These cells were rapidly eliminated by phagocytosis, mainly by other muscle cells. Following their incorporation into other muscle cells, the cells gradually became transformed into heterogeneous electron-dense bodies with the features of heterophagosomes.