Inducible nitric oxide synthase increases secretion from inflamed salivary glands.
OBJECTIVE
Salivary gland secretion is dependent on cholinergic stimulation via autonomic nerves and calcium signalling in acinar cells. Secretory dysfunction associated with SS may be partly caused by the damaging effects of increased glandular concentrations of nitric oxide (NO) derived from up-regulation of inducible NO synthase (iNOS) that accompanies glandular inflammation. The present study examines the effects of increased iNOS expression on salivary gland secretory function.


METHODS
The inflammogen lipopolysaccharide (LPS) was introduced intraductally into rat submandibular glands, and glandular responsiveness to cholinergic stimulation was determined.


RESULTS
LPS provoked a rapid, long-lasting inflammation, increasing gland weight (by almost 20%) and inflammatory cell infiltration at 3 and 24 h. Immunoblotting of glandular homogenates indicated that iNOS expression was increased approximately 4-fold, and immunohistochemistry of frozen tissue sections showed increased iNOS expression in acinar cells. Salivary secretion from inflamed glands was significantly increased in response to low doses of methacholine and accompanied by increased acinar cell calcium signalling in vitro. Prior administration of the iNOS inhibitors, aminoguanidine or L-NIL [L-N6-(1-iminoethyl)-lysine dihydrochloride] abolished increased secretion and acinar cell calcium signalling.


CONCLUSIONS
Up-regulation of glandular iNOS expression can increase cholinergically evoked salivary secretion and appears to offset any secretory hypofunction linked with glandular inflammation. It seems unlikely that increased glandular levels of NO are responsible for the secretory hypofunction that accompanies SS.
Correia
Patricia N
PN
Salivary Research Unit, King's College London Dental Institute, Guy's and St Thomas' Hospitals, Great Maze Pond, London SE1 9RT, UK.
Carpenter
Guy H
GH
Paterson
Katherine L
KL
Proctor
Gordon B
GB
D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D004195:Disease Models, Animal; D008070:Lipopolysaccharides; D008297:Male; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism / Q000502:physiology*; D009929:Organ Size; D051381:Rats; D017208:Rats, Wistar; D012793:Sialadenitis / Q000139:chemically induced / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology*; D012859:Sjogren's Syndrome / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D013363:Submandibular Gland / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D015854:Up-Regulation
D008070:Lipopolysaccharides; D052247:Nitric Oxide Synthase Type II