Salivary secretion of highly concentrated chromogranin a in response to noradrenaline and acetylcholine in isolated and perfused rat submandibular glands

Chromogranin A (CgA) is a member of a family of highly acidic proteins, chr omogranins, which are co-stored in the adrenergic neurons and paraneurons a nd co-released with adrenaline and noradrenaline (NAd) in response to adequ ate stimulation. The present study provides novel evidence that CgA-like im munoreactivity (IR) is stored in the exocrine cells in the granular convolu ted tubule, and is secreted into saliva by stimulation with NAd and acetylc holine (ACh) in the isolated and perfused rat submandibular gland. NAd at 1 mu M produced maximum secretion of CgA-like IR (less than or equal to 0.9 mM) and a marked increase in salivary flow. Further increases in NAd concen tration (10 or 100 mu M) yielded concentration-dependent decreases in both responses. ACh at 1 mu M produced maximum salivary flow and a slight elevat ion of CgA-like IR secretion (6 mu M); 100 mu M 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 t he cells of the granular convoluted tubule when the submandibular gland was stimulated with 1 mu M NAd. These results provide an experimental basis fo r the view that the salivary CgA-Iike IR secretion may be a sensitive and q uantitative index of the activity of the sympathetic nervous system innerva ting the gland.