Effects of mastication on the secretory and proliferative capabilities of parotid gland in male rat

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Four week-old rats were fed for3 (4-week-old rat)-9 weeks (13-week-old rat) with solid or powdered MF feed of Oriental Yeast Co.and the responsiveness of parotid gland to sialagogues (carbachol and isoproterenol) was examined with parotid explants which were cultured on siliconized lens paper (Kawano et al., J.Dent.Res.71,1885-1890,1992).The results were as follows ;1) The increases of body weights, 90g (4-week-old rats) to 450g (13-week-old rats), were the same among the two feed groups but an average weight of parotid gland was heavier (about 20%) in solid group than in powder group in 3-9-week-treated rats (7-13-week-old rats).2) Sialagogue-dependent increase in amylase secretion was higher in solid group than in powder group (7-week-old rats), but no significant difference was observed between two groups of older than 9-week-old rats.3) Sialagogue-induced increases in mRNA levels of c-fos, c-myc and ornithine decarboxylase and activity of the enzyme were higher in solid group than powder group during entire period of experiment (7-13-week-old rats).These results indicate that the effects of carbachol and isoproterenol on amylase secretion and cell proliferation in parotid gland were marked in solid group than in powder group, suggesting that physical pressure and frequency of mastication participate the responsiveness of parotid gland to both sympathetic and parasympathetic stimuli.