Radioprotective effect of lidocaine on neurotransmitter agonist-induced secretion in irradiated salivary glands.

Previously we verified the radioprotective effect of lidocaine on
the function and ultrastructure of salivary glands in rabbits.
However, the underlying mechanism of lidocaine's radioprotective
effect is unknown. We hypothesized that lidocaine, as a membrane
stabilization agent, has a protective effect on intracellular
neuroreceptor-mediated signaling and hence can help preserve the
secretory function of salivary glands during radiotherapy. Rabbits
were irradiated with or without pretreatment with lidocaine before
receiving fractionated radiation to a total dose of 35 Gy.
Sialoscintigraphy and saliva total protein assay were performed
before radiation and 1 week after the last radiation fraction.
Isolated salivary gland acini were stimulated with either carbachol
or adrenaline. Ca(2+) influx in response to the stimulation with
these agonists was measured using laser scanning confocal
microscopy. The uptake of activity and the excretion fraction of
the parotid glands were significantly reduced after radiation, but
lidocaine had a protective effect. Saliva total protein
concentration was not altered after radiation. For isolated acini,
Ca(2+) influx in response to stimulation with carbachol, but not
adrenaline, was impaired after irradiation; lidocaine pretreatment
attenuated this effect. Lidocaine has a radioprotective effect on
the capacity of muscarinic agonist-induced water secretion in
irradiated salivary glands.