Mechanism of Experimental Tumorigenesis. V. Ultrastructural Alterations in Mouse Epidermis Caused by Span 60 and Tween 60-Type Agents2

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Abstract
Electron microscopic studies of the same material that previously had been analyzed histoquantitatively and by light microscopy demonstrated that all laboratory-synthesized products derived from Span 60 (sorbitan monostearate) brought about a special “Span 60 effect” in the interfollicular epidermis (IFE) of the back of the mouse. Correspondingly, all products of Tween 60 type (polyoxyethylene sorbitan monostearate), which were obtained by adding, on an average, 20 units of ethylene oxide to these Spans, caused the “Tween 60 effect.” These two effects essentially differed from each other in both electron microscopic and light microscopic studies. All Span 60-type agents caused an accumulation of electron-dense material in the cytoplasm of basal cells, but no IFE hyperplasia. All Tween 60-type agents induced a high-degree IFE hyperplasia that lasted as long as the treatment. The daughter cells were cast off from their basal parents in a too-early stage of their maturation. This led to a consecutive, (i.e., secondary, and nonspecific delay in maturation of the epidermal cells. Simultaneously, cells in differentiation increased in amount. Except for the basal cells, all other cells in IFE hyperplasia caused by Tween 60-type agents were nonviable—doomed to die by differentiation.