β-Adrenoceptors in the rat parotid gland enlarged by salivariectomy and bulk diet. Effects of denervation

Abstract

The numbers of β-adrenergic receptors and level of cyclic AMP (cAMP) of the parotid gland of adult female rats were determined 4 weeks after introduction of a regimen that induced a 2-fold increase in gland weight. This regimen consisted of ablation of the submandibular-sublingual glands and substitution of the normal chow diet with a bulk diet consisting of 50% inert cellulose and 50% ground solid chow. There was a 2.4-fold increase in number (density) of β-adrenoceptors in the enlarged parotid gland when comparison was made with parotid glands of control rats. The β-adrenoceptor present in the enlarged and normal glands was of the β 1 subtype. Removal of either autonomic pathway at the time of partial salivariectomy and dietary substitution was followed by a small reduction in number of β-adrenoceptors (4–9% with either denervation), but when both nerves were removed the reduction was 25%; in magnitude, these changes were generally similar to those observed with denervated parotid glands of chow-fed rats. The norepinephrine concentration of the enlarged gland was much less than that of normal glands (reduced 38%); sympathectomy of normal or enlarged parotid glands resulted in a marked lowering of norepinephrine concentrations (to 1–5% of control levels): parasympathectomy had no effect on norepinephrine concentration of enlarged parotid glands but caused a decrease in that of the parotid of normal size. Apparently, the number of β-adrenoceptors depends on the degree of activity of both the parasympathetic and sympathetic nerves to the parotid. The level of cAMP was elevated in the enlarged parotid gland and was more than 6 times as high as that of control parotid glands.