Hyperplasia of myoepithelial cells expressing calponin during atrophy of the rat parotid gland induced by duct ligation

The number and location of myoepithelial cells in the rat parotid gland submitted to surgical ligation of its main excretory duct were studied through immunohistochemical labelling for calponin. These cells were labelled by the streptavidin-biotin method using anti-calponin primary antibody, and their number was determined during each step of glandular atrophy, i.e., at time zero (control) and 1, 7, 15, 21, 30 and 60 days after ligation. Morphological analysis showed a gradual decrease and fibrosis of the glandular lobules accompanied by disappearance of the acini and the occurrence of duct-like structures. The expression of calponin was observed in all specimens analysed, being restricted to myoepithelial cells. Labelling revealed the distribution of myoepithelial cells around the acini and intercalated ducts in the control group and around duct-like structures later during the course of atrophy. Quantitative analysis demonstrated significant increase in the number of myoepithelial cells up to day 7 post-ligation, followed by gradual increases which, however, were not statistically significant. These results suggest that myoepithelial cells proliferate intensely up to day 7 post-ligation, an event that coincides with a higher rate of disappearance of acinar cells. After this period, the elevated number of cells observed at the end of the previous period is maintained.