Mitochorial form in hepatic parenchymal cells in rats of several ages

Slices of livers from neonatal, 7-day-old and adult rats were fixed in osmium tetroxide or a formaldehyde-osmium tetroxide sequence and processed for electron microscopy. Mitochondria from neonatal hepatic parenchymal cells are pleomorphic. Disc-shaped forms are common. In 7-day-old animals, cylinders are the most numerous single form, discs are present but smaller, and spherical forms increase in number. In the adult, mitochondria are predominantly cylindrical in form. The average volume of neonatal mitochondria is greater than that of 7-day-old or adult mitochondria.