Role of submandibular salivary glands in LPS-induced lung inflammation in rats

Literature data suggest that rodent salivary glands can exert a neuroimmunomodulatory influence on distant inflammatory events. The release of regulatory factors by salivary glands appears to be influenced by time-dependent factors. In this paper we examined this possibility directly by studying the role of submandibular salivary glands in the temporal profile of lypopolysaccharide (LPS)-induced lung inflammation in rats.

The submandibular glands were removed (SMGx) or not (sham) and, 4 days later, the animals received an intravenous LPS injection (Salmonella abortus equi, 1 mg/kg). Cells in peripheral blood and in bronchoalveolar and bone marrow lavages were quantified after 90 min, 1, 3 and 5 days. Tumor necrosis factor (TNF) activity and corticosterone concentrations in serum were also determined. Baseline values were determined in a group of naïve rats.

One day after the LPS injection, neutrophil counts in lungs and blood in both animal groups were elevated, but the SMGx rats presented a significantly lower response in comparison to the sham-operated controls. Five days after LPS treatment, however, SMGx rats had higher neutrophil counts in the lungs than did sham animals, but numbers of blood neutrophils were equal. Ninety minutes after LPS injection, a peak of serum TNF activity was detected in both groups compared with naïve levels. At this time point, TNF activity was about 135% higher in the serum of the SMGx group than in controls. Corticosterone levels of sham-operated controls rose only on the 5th day after LPS, whereas SMGx rats had significant peaks of corticosterone both on the 1st and the 5th day, but not on the 3rd day.

Our data indicate that submandibular glands have a dual effect on inflammatory pulmonary response by differentially modulating the profile of lung neutrophil influx.