Response of rat salivary glands to mastication of pelleted vitamin A-deficient diet.

Interpretation of previous studies of the effects of hypovitaminosis. A on salivary glands is confounded by the atrophic effects of liquid or powdered diets. The purpose of this study was to reevaluate the effects of vitamin. A deficiency on the morphology and function of rat salivary glands using a pelleted diet that promotes physiological levels of masticatory stimulation. Profound vitamin A deficiency resulted in a marked decrease in stimulated parotid secretion. Histological evaluation demonstrated the development of squamous metaplasia in the ducts of parotid, submandibular and sublingual salivary glands; however, atrophy was observed only in serious salivary glands. In the parotid gland the degree of atrophy corresponded to the decrease in stimulated secretion. Mild hypovitaminosis A (before the development of squamous metaplasia in ducts) was associated with distinctly different effects. The parotid gland was moderately enlarged. There was also a significant increase in stimulated secretion, which was not explained by changes in gland size, muscarinic receptor number or affinity, or receptor-mediated calcium signalling.