Action of metabolic hormones on the fine structure of rat liver cells. I. Effects of fasting on the ultrastructure of hepatocytes

This report provides information on the ultrastructure of liver parenchymal cells from rats fasted 2, 15–21, and 21–40 hours. Fasting rats from 2 through 40 hours provokes alterations in the quantity and patterns of glycogen, amounts and forms of the rough endoplasmic reticulum, and the quantity of smooth endoplasmic reticulum in hepatocytes. After two hours of fasting glycogen occurs as clumps of α particles in restricted areas of the cytosome, the smooth endoplasmic reticulum is relatively sparse, and the rough endoplasmic reticulum is displayed as parallel cisternae comprising the characteristic basophilic bodies of the hepatocyte. Fasting the rat for 15 hours and longer decreases the amount of hepatic glycogen which appears predominantly as β particles in restricted regions of the liver cell. The prolonged fast provokes a dramatic proliferation of smooth endoplasmic reticulum in the liver parenchymal cell. The tubules of this organelle are continuous with the cisternae of rough endoplasmic reticulum and extend deep into the glycogen areas of the hepatocyte. Arguments are presented to support the concept that the smooth endoplasmic reticulum develops from rough endoplasmic reticulum and that its membranes provide a site for the location of enzymes involved in glycogen metabolism.