PARASYMPATHETIC NONADRENERGIC, NONCHOLINERGIC MECHANISMS IN SALIVARY-GLANDS AND THEIR ROLE IN REFLEX SECRETION

Parasympathetic atropine-resistant vasodilatation is a well-known phen omenon in salivary glands. Less well known is the fact that there also exists an atropine-resistant secretory response to parasympathetic st imulation: some glands secrete saliva. albeit at a reduced rate, where as others just release protein and acinar secretory granules. A number of peptides, including vasoactive intestinal peptide (VIP) and substa nce P, are likely to be involved in the se called nonadrenergic, non-c holinergic (NANC) transmission of the parasympathetic secretory impuls es. We here report a series of experiments where we have found these N ANC-mechanisms to be mobilized during reflex secretion. Loss of acinar granules, morphometrically assessed, and reduction in glandular amyla se activity indicated secretory activity in the parotid gland of the c onscious rat, in the presence of atropine and adrenoceptor antagonists , in response to food intake. As judged by these indices, the NANC mec hanisms were potentially responsible for the whole parasympathetic res ponse and, thus, for the major part of the marked response in the abse nce of the antagonists. Furthermore, the reflex mobilization of the NA NC mechanisms depended on mastication rather than on taste, and involv ed the release of VIP and substance P. The results presented give weig ht 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.