Autonomic control of salivary secretion

The view is generally held that the secretory elements of the major salivary glands are supplied with parasympathetic (cholinergic) nerve fibres, while the extent of the sympathetic (adrenergic) innervation varies considerably not only between different species but also between the glands of the same species. Parasympathetic stimulation evokes a copious flow of saliva. In contrast, sympathetic stimulation produces either a small flow, which is rich in protein, or no flow at all. In recent years it has become evident that secretion of saliva may not be elicited only by cholinergic or adrenergic agonists but also by peptides, injected into the bloodstream, and further, that the salivary secretion in response to stimulation of the parasympathetic innervation is not always completely abolished by the muscarinic receptor blocker atropine (and adrenoceptor antagonists). The present communication focuses on this "atropine-resistant" parasympathetic influence on the salivary glands and on a possible role for neuropeptides in mediating "atropine-resistant" parasympathetic responses in the glands. Immediate effects as well as long-term trophic effects are considered.