Effects of food mastication on rat parotid gland adrenergic and cholinergic cell surface receptors.

Adult male rats were fed diets of differing texture (liquid, powder, standard pelleted, or bulk pelleted) to alter food mastication. After 2 weeks, the parotid glands were removed and adrenergic and muscarinic-cholinergic cell surface receptor density (fM bound/mg protein) and ligand binding dissociation constants (Kd in nM) were determined by radioligand binding techniques on a crude membrane fraction. For all diets, gland weight increased as the requirement for food mastication increased (i.e., liquid < powder < standard pelleted < bulk pelleted). Among the diets, neither beta-two nor alpha-two receptor density was altered. Beta-one receptor density was directly related to dietary mastication. Compared with the standard pelleted diet, beta-one receptor density was reduced 21% for the liquid diet and 7% for the powdered diet; for the bulk-pelleted diet, beta-one receptor density was increased 11%. With respect to alpha-one receptor density, it was not affected by the liquid or powdered diet when compared with the standard pelleted diet, but alpha-one receptors were increased 14% with the bulk-pelleted diet. Muscarinic-cholinergic receptor density for the liquid diet fed rats was 27% less than for the standard-pelleted diet; powdered diet did not differ from standard pelleted, while that for the bulk-pelleted diet was increased 6%. With but minor exceptions, ligand binding affinity was unaffected by the changes in diet texture. These studies demonstrate that dietary mastication as well as affecting parotid gland weight, cell size, and saliva production also influences autonomic cell surface receptor density.