SALIVARY SECRETION OF HIGHLY CONCENTRATED CHROMOGRANIN A IN RESPONSE TO NORADRENALINE AND ACETYLCHOLINE IN ISOLATED AND PERFUSED RAT SUBMANDIBULAR GLANDS

Abstract

Chromogranin A (CgA) is a member of a family of highly acidic proteins, chromogranins, which are co-stored in the adrenergic neurons and paraneurons and co-released with adrenaline and noradrenaline (NAd) in response to adequate stimulation. The present study provides novel evidence that CgA-like immunoreactivity (IR) is stored in the exocrine cells in the granular convoluted tubule, and is secreted into saliva by stimulation with NAd and acetylcholine (ACh) in the isolated and perfused rat submandibular gland. NAd at 1 μM produced maximum secretion of CgA-like IR (<< 0.9 mM) and a marked increase in salivary flow. Further increases in NAd concentration (10 or 100 μM) yielded concentration-dependent decreases in both responses. ACh at 1 μM produced maximum salivary flow and a slight elevation of CgA-like IR secretion (6 μM); 100 μM ACh decreased the salivary flow but increased the CgA-like IR secretion (0.6 mM). Electron microscopic examination showed vigorous compound exocytosis of secretory granules in the cells of the granular convoluted tubule when the submandibular gland was stimulated with 1 μM NAd. These results provide an experimental basis for the view that the salivary CgA-like IR secretion may be a sensitive and quantitative index of the activity of the sympathetic nervous system innervating the gland.