The effect of actinomycin D on the fibroblast of the pulp of the rat incisor : A study by quantitative radioautography and electron microscopy

Abstract

The effect of actinomycin D on the fibroblast of the dental pulp of continuously growing rat incisors is studied by means of radioautography and electron microscopy. Results of grain counts of radioautographs at various times following an injection of H3-leucine indicate that there is a progressive decrease in incorporation of the isotope by fibroblasts which reaches a maximum decrease on day 7 and subsequently regenerate to a near normal value by the end of the experiment on day 21.Electron microscopic observations of the fine structure of the fibroblast parallel the radioautographic findings in that the maximum degeneration of intracellular structures is observed on day 7 with gradual recovery from that point on. The most seriously affected structures are the rough surfaced endoplasmic reticulum, the Golgi apparatus and the appearance of polyribosomes, the structures that are thought to be directly involved in the elaboration and secretion of proteins. In addition, increased irregularity in size and shape of mitochondria is observed. A large number of lipid droplets as well as cytolysomes appear during the period between 7 and 10 days. The observations on the nucleolus confirm descriptions by previous workers.