Background: The moisture content of diet and the dryness of the mouth alter the volume of parotid saliva secreted in rats and it plays an important part in mastication and swallowing. Temporary or permanent liquid diet feeding provides a nutritional regime for patients in certain medical situations. The aim of the present work is to investigate the sequel of liquid diet on parotid gland in rats and the possible protective role of L-carnitine (L-car).

Materials and methods: Thirty adult male albino rats were divided into three groups (10 per group) — Control group: rats were fed on regular pellet diet, Liquid diet group and Liquid diet supplemented with L-car group were received liquid diet. The parotid glands were dissected for histological, immunohistochemical and ultrastructural analysis.

Results: By light microscope, liquid fed group showed some areas with degenerated irregularly shaped acini and atrophic acini with vacuolated cytoplasm and pyknotic nuclei. Acinar cells of parotid gland group on liquid diet supplemented with L-car, had normally eosinophilic cytoplasm with few vacuoles in their acinar cells. Periodic acid Schiff (PAS) staining, in liquid fed group showed that the serous acini were weakly stained with PAS that was localised in the apical portion of the cells where the secretory granules lie with lack of staining of the vacuoles. However, moderately stained acinar epithelial cell and fewer vacuoles was seen in group given liquid diet supplemented with L-car. Immunohistochemistry of Caspase 3 showed more apoptotic cells with increased area per cent of Caspase 3 immunoexpression, seen in the acini and more in the ductal epithelium in liquid fed group. It was markedly reduced in the acinar cells in group on liquid diet supplemented with L-car. Electron microscopic study revealed in liquid fed group acini with multiple cytoplasmic vacuoles and reduced secretory granules, degenerated swollen mitochondria and dilated cisternae of endoplasmic reticulum. Degenerated condensed nuclear mass or indented nuclear membrane, nuclei with karyorrhexis and chromatin material leaked in the cytoplasm with rupture of the nuclear membranes were also seen. In parotid gland of liquid fed group supplemented with L-car, acinar cells showed normally distributed secretory granules and few cytoplasmic vacuoles. They showed normal appearance of the nuclei and their cytoplasmic organelles.

Conclusions: Liquid diet caused cellular degenerative damages and apoptotic changes in parotid gland and these changes can be prevented by L-car supplementation probably by its antioxidant properties.