Parasympathetic non-adrenergic, non-cholinergic mechanisms in salivary glands and their role in reflexly elicited glandular responses

Abstract

The very first report of a parasympathetic Non-Adrenergic, Non-Cholinergic (NANC) transmitter response was done by Heidenhain (1872), who found an increased blood flow in the submandibular gland of the atropinized dog in response to electrical stimulation of the chorda-lingual nerve. The general view has been that parasympathetic nerve-evoked secretion in salivary glands is easily abolished by atropine, and that the transmitter mediating the response is acetylcholine. Salivary secretion is elicited by impulses in the autonomic nervous system as a response to various afferent stimuli. The aim of this thesis, was to further investigate the role of NANC transmitters in parotid salivary gland responses, especially during reflex activation. As an indicator of glandular activity the loss of acinar secretory granules and the amylasecontent were estimated. Different stimuli were used, eletrical nerve stimulation, infusion of neuropeptides such as vasoactive intestinal peptide (VIP), substance P (SP) separately/combination in the unconscious rat and cat, and reflexstimulation in the rat by feeding. The influence of catecholamines on the degranulation was also studied. It is concluded that the NANC transmitters evoke acinar degranulation and loss in amylase activity and are part of salivary reflexes set up in response to for example mastication.....It is also shown that the neuropeptides are economized, when acting together with the classical transmitter acetylcholine.Glands stimulated by reflexes or by electrical nerve stimulation were usually surrounded by an oedema, and there are reports about associations with general anaesthesia and use of belladonna alkaloids and oedema formation in the parotid gland. Therefore a role for NANC mechanisms in inducing microvascular leakage i parotid gland tissue was examined by measuring changes in vascular permeability for plasma proteins labelled by Evans blue. For instance neurokinin A resulted in a 75 % increase in the accumulation of Evans blue in the parotid gland.NANC transmitters conveying parasympathetic impulses are potential contributor to the secretory response of the gland under reflex conditions.