Nerve-evoked secretion of immunoglobulin A in relation to other proteins by parotid glands in anaesthetized rat

Secretion of fluid and proteins by salivary cells is under the control of parasympathetic and sympathetic autonomic nerves. In a recent study we have shown that, in the rat submandibular gland, autonomic nerves can also increase the secretion of IgA, a product of plasma cells secreted into saliva as SIgA (IgA bound to Secretory Component, the cleaved poly-immunoglobulin receptor). The present study aimed to determine if parotid secretion of SIgA is increased by autonomic nerves and to compare SIgA secretion with other parotid proteins stored and secreted by acinar and ductal cells. Assay of IgA in saliva evoked by parasympathetic nerve stimulation immediately following an extended rest period under anaesthesia indicated that it had been secreted into intraductal saliva in the absence of stimulation during the rest period. The mean rate of unstimulated IgA secretion (2.77+/-0.28 microg min(-1) g(-1)) and the 2.5-fold increase in IgA secretion evoked by parasympathetic stimulation were similar to results found previously in the rat submandibular gland. Sympathetic nerve stimulation increased SIgA secretion 2.7-fold, much less than in the submandibular gland. SDS-PAGE and Western blot analysis with anti-IgA and anti-Secretory Component antibodies confirmed that SIgA was the predominant form of IgA in saliva. Acinar-derived amylase and ductal-derived tissue kallikrein were more profoundly increased by parasympathetic and particularly sympathetic stimulation than SIgA. Overall, the results of the present study indicate that SIgA forms a prominent component of unstimulated parotid salivary protein secretion and that its secretion is similarly increased by stimulation of either autonomic nerve supply. The secretion of other parotid salivary proteins that are synthesized and stored by acinar or ductal cells is upregulated to a much greater extent by parasympathetic and particularly sympathetic stimulation.