Studies on the influence of sensory stimulation (acupuncture) on neuropeptide release in the saliva

Abstract

The aim of this thesis was to elucidate the mechanisms behind the effect of sensory stimulation (acupuncture) on the salivary flow rates of xerostomic patients. We hypothesised that the sensory stimulation activates the sensory and autonomic nervous systems, leading to an increased release of neuropeptides that influence salivary secretion in co-operation with or/and beside the classical neurotransmitters. The neuropeptides also affect blood flow through dilatation of the capillary blood vessels, and in addition have atrophic influence on the salivary gland tissues.

In the first study we investigated the influence of different modes of acupuncture stimulation on the blood flux in the skin overlaying the parotid gland of 21 patients suffering from Sjögren's syndrome. The results showed that there was a significant increase in the blood flux following manual and low frequency electro-acupuncture, which might contribute to the relief of xerostomia.

In the second study the presence of five neuropeptides, substance P (SP), neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY), in the saliva of healthy subjects was investigated using competitive radioimmunoassay (RIA). The results showed that the concentration of the investigated neuropeptides in whole saliva decreased two- to four-fold (up to 16-fold for CGRP) when the volume of saliva increased 6 to 8 times due to stimulation. The released amounts of all the investigated neuropeptides increased over time in the whole saliva two- to five-fold (up to 10-fold for CGRP) in the chewing-stimulated salivary flow as compared to the resting salivary flow or to the citric acid-stimulated flow.

The influence of acupuncture stimulation on the salivary flow rates of eight healthy subjects was investigated in the third study. The results showed that there was a significant increase (p < 0.01) in unstimulated salivary flow both during and after manual acupuncture stimulation as compared to base line levels.

In the fourth study we investigated the influence of different modes of acupuncture stimulation on the release of the neuropeptides: SP, NKA, CGRP, NPY and VIP in the saliva of healthy subjects. The results of our study showed that acupuncture stimulation caused an increase of the concentrations and amounts of VIP-LI, NPY-LI, SP-LI and CGRP-LI released in the saliva. The concentrations and the amounts of these neuropeptides were also increased during the 20-minute-period following the end of the stimulation.

The influence of acupuncture treatment on the release of VIP and CGRP in the saliva of 17 xerostomic patients was investigated in studies V and VI. The concentrations of VIP and CGRP in the saliva were significantly higher (p < 0.05 and p < 0.001, respectively) after the end of acupuncture treatment as compared to the pre-treatment concentrations. We concluded that one of the mechanisms through which the acupuncture stimulation can lead to an increase in the salivary flow rates in xerostomic patients might be the release of VIP and CGRP.

The mechanisms behind the effect of sensory stimulation (acupuncture) might be the activation of sensory afferents as well as parasympathetic efferent neurons leading to an increased release of the neuropeptides VIP and CGRP, which could have dual effect. A direct influence on the salivary flow rates, as well as a long-term effect on the condition of the gland tissues through their trophic influence on the gland- and endothelial-cells, resulting in improvement of glandular function and blood supply of the salivary glands.

Final conclusions: sensory stimulation increases the release of neuropeptides in the saliva leading to an improvement of salivary secretion rates and increased blood flow.