Parasympathectomy increases resting salivary secretion in normal and irradiated submandibular glands of rats

Fluid and ion secretion from the submandibular gland (SMG) is mainly regulated by parasympathetic nerves. This study evaluated the effect of parasympathectomy on salivary secretion from normal and irradiated rat SMGs from 1 to 24 wk after denervation. Although stimulated salivary secretion was significantly lower in denervated SMGs compared with contralateral self-controls, the resting salivary flow rates were markedly higher in the denervated SMGs at 1, 12, and 24 wk after denervation. The levels of muscarinic acetylcholine M1 and M3 receptors, as well as of aquaporin 5, were up-regulated. Notably, although irradiated SMGs showed significantly lower resting and stimulated salivary secretion rates than non-irradiated SMGs, the resting salivary secretion rates of the irradiated and denervated SMGs were markedly higher than seen in the irradiated self-control SMGs at 1, 12, and 24 wk after parasympathectomy, and were even higher than seen in the non-irradiated sham-operated rats. The expression of M1 and M3 receptors was similarly elevated. Taken together, our results suggest that parasympathetic denervation increases resting salivary secretion of both normal and irradiated SMGs. This approach might provide a potential modality for relieving radiation-induced xerostomia, which is a common complication following treatment of head and neck cancer.