Nina Khosravani

Saliva and the Control of Its Secretion

The various functions of saliva—among them digestive, protective and trophic ones—not just limited to the mouth, and the relative contribution of the different types of gland to the total volume secreted as well as to various secretory rhythms over time are discussed. Salivary reflexes, afferent and efferent pathways, as well as the action of classical and non-classical transmission mechanisms regulating the activity of the secretory elements and blood vessels are in focus. Sensory nerves of glandular origin and an involvement in gland inflammation are discussed. Although, the glandular activities are principally regulated by nerves, recent findings of an “acute” influence of gastro-intestinal hormones on saliva composition and metabolism, are paid attention to, suggesting, in addition to the cephalic nervous phase, both a regulatory gastric and intestinal phase. The influence of nerves and hormones in the long-term perspective as well as old age, diseases and consumption of pharmaceutical drugs on the glands and their secretion are discussed with focus on xerostomia and salivary gland hypofunction. Treatment options of dry mouth are presented as well as an explanation to the troublesome clozapine-induced sialorrhea. Final sections of this chapter describe the families of secretory salivary proteins and highlight the most recent results obtained in the study of the human salivary proteome. Particular emphasis is given to the post-translational modifications occurring to salivary proteins before and after secretion, to the polymorphisms observed in the different protein families and to the physiological variations, with a major concern to those detected in the pediatric age. Functions exerted by the different families of salivary proteins and the potential use of human saliva for prognostic and diagnostic purposes are finally discussed.

The otic ganglion in rats and its parotid connection: cholinergic pathways, reflex secretion and a secretory role for the facial nerve

Otic ganglionectomy in rats was found to have affected the parotid gland more profoundly than section of the auriculotemporal nerve as assesssed by reduction in gland weight (by 33 versus 20%) and total acetylcholine synthesizing capacity (by 88 versus 76%) 1 week postoperatively and, when assessed on the day of surgery under adrenoceptor blockade, by reflex secretion (by 99 versus 88%). The facial nerve contributed to the acetylcholine synthesizing capacity of the gland. Section of the nerve only, at the level of the stylomastoid foramen, reduced the acetylcholine synthesis by 15% and, combined with otic ganglionectomy, by 98% or, combined with section of the auriculotemporal nerve, by 82%. The facial nerve was secretory to the gland, and the response was of a cholinergic nature. The nerve conveyed reflex secretion of saliva and caused secretion of saliva upon stimulation. Most of the facial secretory nerve fibres originated from the otic ganglion, since after otic ganglionectomy (and allowing for nerve degeneration) the secretory response to facial nerve stimulation was markedly reduced (from 23 to 4 μl (5 min)−1). The persisting secetory response after otic ganglionectomy, exaggerated due to sensitization, and the residual acetylcholine synthesizing capacity (mainly depending on the facial nerve) showed that a minor proportion of pre‐ and postganglionic nerve fibres relay outside the otic ganglion. The great auricular nerve, which like the facial nerve penetrates the gland, caused no secretion of saliva upon stimulation. Avulsion of the auriculotemporal nerve was more effective than otic ganglionectomy in reducing the acetylcholine synthesizing capacity (by 94 versus 88%) and as effective as otic ganglionectomy in abolishing reflex secretion (by 99%). When aiming at parasympathetic denervation, avulsion may be the preferable choice, since it is technically easier to perform than otic ganglionectomy.

Altered plasticity of the parasympathetic innervation in the recovering rat submandibular gland following extensive atrophy.

Adult rat submandibular glands have a rich autonomic innervation, with parasympathetic and sympathetic nerves working in synergy rather than antagonistically. Ligation of the secretory duct rapidly causes atrophy and the loss of most acini, which are the main target cell for parasympathetic nerves. Following deligation, there is a recovery of gland structure and function, as assessed by autonomimetic stimulation. This study examines whether the parasympathetic nerves reattach to new target cells to form functional neuro‐effector junctions. Under recovery anaesthesia, the submandibular duct of adult male rats was ligated via an intra‐oral approach to avoid damaging the chorda‐lingual nerve. Four weeks later, rats were either killed or anaesthetized and the ligation clip removed. Following a further 8 weeks, both submandibular ducts were cannulated under terminal anaesthesia. Salivary flows were then stimulated electrically (chorda‐lingual nerve at 2, 5 and 10 Hz) and subsequently by methacholine (whole‐body infusion at two doses). Glands were excised, weighed and divided for further in vitro studies or fixed for histological examination. Ligation of ducts caused 75% loss of gland weight, with the loss of most acinar cells. Of the remaining acini, only 50% were innervated despite unchanged choline acetyltransferase activity, suggesting few parasympathetic nerves had died. Following deligation, submandibular glands recovered half their weight and had normal morphology. Salivary flows from both glands (per unit of gland tissue) were similar when evoked by methacholine but greater from the deligated glands when evoked by nerve stimulation. This suggests that parasympathetic nerves had reattached to new target cells in the recovered glands at a greater ratio than normal, confirming reinnervation of the regenerating gland.

The cholinesterase inhibitor physostigmine for the local treatment of dry mouth: a randomized study

Application of physostigmine to the oromucosal surface with the aim of stimulating underlying mucin-producing glands while reducing cholinergic systemic effects might be a strategy for treating dry mouth. Subjects suffering from dry mouth and with hyposalivation participated in a crossover, double-blind, randomized study. A gel containing physostigmine (0.9, 1.8, 3.6, and 7.2 mg) or placebo was applied to the inside of the lips and distributed with the tongue. The feeling of dryness was assessed using a visual analogue scale (VAS) (where a score of 100 = extremely dry) and systemic effects were registered. Based on assessments of efficacy and safety, the dose of 1.8 mg of physostigmine was selected for use in the second part of the study to make objective measurements of saliva volumes. Physostigmine (1.8 mg) produced long-lasting (120 min) relief (evident as a score reduction of 25 on the VAS) in the feeling of dryness. Judging from AUC values related to baseline over 180 min, the improvement for both mouth and lips in response to physostigmine was six times greater than that to placebo. At higher doses of physostigmine, gastrointestinal discomfort predominantly occurred. The volume of saliva collected in response to physostigmine was five times higher over 180 min than that collected in response to placebo. Physostigmine, applied locally, therefore appears to be a promising modality for dry-mouth treatment.

RP-HPLC-ESI-MS characterization of novel peptide fragments related to rat parotid secretory protein in parasympathetic induced saliva.

Two peptides (MW 1211.7 and 928.5 Da) were detected by RP-HPLC-ESI-MS analysis of parotid saliva secreted upon continuous parasympathetic stimulation. The peptide with the higher mass (PSPFr-A) corresponded to the N-terminal dodecapeptide (Fragment 1-12) of rat parotid secretory protein (PSP), while the peptide with the lower mass (PSPFr-B) corresponded to the 4-12 fragment of the same protein. During stimulation, the PSPFr-A secretion increased, while the PSPFr-B secretion decreased (HPLC-ESI-MS). In the presence of cycloheximide, PSPFr-A was not demonstrated, while the PSPFr-B secretion decreased. In the presence of aprotinin, the PSPFr-B secretion was almost abolished, while the PSPFr-A secretion increased to higher levels than those observed in the absence of the inhibitor. In vitro perfusion, with artificial solution, of stimulated rat parotid glands excluded that the fragments were derived from the circulation. Neither peptide occurred in enriched granule preparations from unstimulated glands. The results suggest that at least two pathways--granular and vesicular--are responsible for the generation of the two peptides. PSPFr-A is the first cleavage product in both pathways. PRPFr-B is probably generated from granular PSPFr-A only and, at the end of the granule mediated pathway, by the action of an enzyme of the serine protease class.