Sebaceous gland hyperplasia on rabbit pinna induced by tetradecane

To investigate the pathologic changes of sebaceous glands during comedo formation induced by topically applied substances in a rabbit pinna model, purified tetradecane was inuncted on the ventral aspect of the rabbit pinnas once a day for a week. Histologically, a marked hyperplasia of sebaceous glands, epidermis, and follicular epithelium was seen. These remarkably enlarged sebaceous glands were examined histochemically and ultrastructurally. The acinus size and cell population of the hyperplastic sebaceous gland were significantly increased over those of the normal sebaceous gland. By N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide staining, normal distribution patterns of sulfhydryl (SH) and disulfide (SS) were seen in the peripheral to differentiating layers in the hyperplastic sebaceous glands. In the terminally differentiated layer, the brilliant SH fluorescence was gradually decreased and the SS fluorescence was gradually increased in intensity, indicating that most SH groups in the sebaceous cells were converted to SS linkages before holocrine secretion. By transmission electron microscopy, several cell layers of undifferentiated sebaceous cells were observed at the periphery of the large sebaceous gland. The differentiating sebaceous cells produced a large number of lipid droplets, which were produced in either rough or smooth endoplasmic reticulum. These cells were abruptly converted into homogeneously electron-dense cells which formed several layers. These homogeneous cells gradually lost their electron density before holocrine secretion. These findings indicate that the sebaceous cells in the hyperplastic sebaceous glands undergo a magnified step-by-step cell differentiation and play a role in slightly modified lipid formation, and that there may be an increased production of sebum in the rabbit pinna model. This is the first report of sebaceous hyperplasia induced by a topically applied substance on skin surface, except for androgens. The hyperplastic sebaceous glands could serve as a model for investigations of sebaceous cell differentiation and lipid formation.