Fine structure of hepatocytes from fasted and fed rats.

The fine structure of hepatocytes from rats maintained on a controlled feeding schedule are described. Liver samples were processed for electron microscopy, histochemistry and chemical determinations of glycogen at precise time-intervals following a 30-hour fast and a 2-hour meal. Hepatocytes from 30-hour-fasted rats with extremely low hepatic glycogen levels were devoid of glycogen particles. Centrilobular cells showed areas of the cytoplasm rich in vesicles of smooth endoplasmic reticulum (SER) while periportal hepatocytes contained less extensive regions of SER. Soon after feeding the fasted rats, glycogen particles appeared in regions of the cell rich in SER. Centrilobular hepatocytes contained numerous glycogen areas which were infiltrated with tubules of SER, while periportal cells showed dense glycogen deposits with SER restricted to the periphery of the masses of glycogen. Throughout glycogen deposition each glycogen particle was closely associated with membranes of SER until maximum glycogen deposition was achieved 12 hours after initiation of feeding. At this point SER was reduced to the lowest amounts of the time-periods studied. During stages of glycogen depletion SER proliferated and reached the highest concentration measured in this study. Tubules of SER were present throughout the glycogen masses of centrilobular hepatocytes, whereas in periportal cells the organelle was restricted to the periphery of the glycogen masses. It is concluded that SER is associated with glycogen particles in rat hepatocytes during both deposition and depletion of glycogen.