Parasympathetic non-adrenergic, non-cholinergic mechanisms in salivary glands and their role in reflex secretion.

Parasympathetic atropine-resistant vasodilatation is a well-known phenomenon in salivary glands. Less well known is the fact that there also exists an atropine-resistant secretory response to parasympathetic stimulation: some glands secrete saliva, albeit at a reduced rate, whereas others just release protein and acinar secretory granules. A number of peptides, including vasoactive intestinal peptide (VIP) and substance P, are likely to be involved in the so called non-adrenergic, non-cholinergic (NANC) transmission of the parasympathetic secretory impulses. We here report a series of experiments where we have found these NANC-mechanisms to be mobilized during reflex secretion. Loss of acinar granules, morphometrically assessed, and reduction in glandular amylase activity indicated secretory activity in the parotid gland of the conscious rat, in the presence of atropine and adrenoceptor antagonists, in response to food intake. As judged by these indices, the NANC mechanisms were potentially responsible for the whole parasympathetic response and, thus, for the major part of the marked response in the absence of the antagonists. Furthermore, the reflex mobilization of the NANC mechanisms depended on mastication rather than on taste, and involved the release of VIP and substance P. The results presented give weight to a physiological role for these mechanisms, and support the idea that, under normal conditions, the NANC mechanisms act in concert with cholinergic and adrenergic mechanisms to generate the most purposeful secretory reflex response to the afferent stimulation.