The effects of moderate protein deficiency on beta-adrenoceptor density in rat parotid and submandibular salivary glands.

The effects of moderate protein deficiency on the number and dissociation constant of beta-adrenergic receptors were investigated. One group of adult rats was fed a protein-deficient diet (5% protein), a control group was given a similar diet with 20% protein, and a third group was fed a standard pellet diet. After 21 days, the salivary glands were removed and the cell membranes were isolated. The binding of [3H]-dihydroalprenolol to cell membranes was measured, with or without the presence of timolol, a potent beta-adrenoceptor antagonist. The rats fed the 5% protein diet had fewer beta-adrenoceptors in both the parotid and the submandibular glands than did the 20% protein group, which did not differ from the standard pellet group. The dissociation constant was not affected by protein deficiency. The rats fed the 5% protein diet had a significantly lower gain in body weight, less heavy submandibular glands but heavier parotids than the rats fed 20% protein. Thus the cellular conditions for protein secretion in the salivary glands are impaired during moderate protein deficiency in the adult rat.