An electron microscopic and radioautographic study of the rat parotid gland after actinomycin D administration

Rat parotid glands have been examined by electron microscopy and radioautography (H3‐leucine incorporation) at various intervals following an injection of actinomycin D in the amount of 0.125 μg per gram of body weight. Light microscopic observations confirmed results from previous experiments similar to this. Radioautographs showed a definite drop in number of silver grains in acinar cells of the parotid from experimental animals. This was most pronounced in 7‐day rats which received H3‐leucine four hours prior to sacrifice. Electron microscopic observations revealed a generalized reduction in number and degree of the organization of organelles concerned with protein synthesis. Furthermore, frequent appearances of lipid droplets, cytolysomes and crystalloid structures were noted. Changes of the nucleolus included the reduction of its size and the formation of spherical encapsulated bodies. A brief discussion is made of these results in relation to the biochemical nature of actinomycin effects on protein producing cells.