Rat salivary gland ligation causes reversible secretory hypofunction

Abstract

Aim: To determine the influence of inflammation on salivary secretion. Secretion by salivary glands involves interactions between nerves, blood vessels and salivary cells. The present study investigated the effects of inflammation on rat submandibular gland function following acute ductal obstruction.

Methods: Under recovery anaesthesia a metal clip was placed on the main duct of the submandibular gland. After 24 h salivary secretion was evoked by nerve and methacholine stimulation. For recovery experiments the clip was removed after 24 h and the animal left to recover for 3 days when salivary function was again assessed.

Results: By 24 h of obstruction an inflammatory infiltrate had developed within the obstructed gland and stimulated salivary flows were just 20% of the normal secretion, whilst protein secretion and ion reabsorption were also severely impaired. If ductal obstruction was removed after 24 h the salivary function returned to normal after 3 days of recovery. In vitro analysis of cells from 24-h ligated glands revealed normal changes in intracellular calcium (the main secondary messenger involved in fluid secretion) in response to methacholine stimulation. Protein secretion from isolated cells indicated some changes in particular to methacholine-induced protein secretion although a significant protein secretion was still seen in response to isoprenaline - the main stimulus for protein secretion.

Conclusion: This report demonstrates reversible salivary inhibition associated with an inflammatory infiltrate within the salivary gland.

Figure 2

Parasympathetically stimulated rat submandibular flows from control (white) and 24-h ligated glands (black). The chorda lingual nerve supplying each gland was separately stimulated at 2, 5 and 10 Hz frequency for 5 min each. Mean flow rates (±SD) per gram gland wet weight for both glands were calculated using the unoperated gland weight as the ligated gland was oedematous (see Table 1), n = 3; *only at 10 Hz was a significant difference (P < 0.05) identified between control and ligated glands.

Figure 1

H & E staining of control unoperated rat submandibular gland (a), following 24-h ligation (b) and 3 days after removal of ligation (c). Ligated glands have large numbers of infiltrating inflammatory cells, readily apparent in the increased stroma and interstitial spaces (arrow) whereas control and recovered glands look normal with an absence of inflammatory cells. Scale bar = 30 μm.

Figure 3

Percentage IgA (a) and peroxidase (b) secretion from submandibular cell preparations of the unoperated control (white columns) and the contralateral gland that had previously been ligated for 24 h (black columns). The results are expressed as the mean ± SEM (n = 19 from four separate ligation experiments for IgA and n = 10 from two experiments for peroxidase) secreted as a percentage of the total present in cells and medium; *P < 0.05 compared with cells of the contralateral gland for the same treatment, +P < 0.05 compared with the unstimulated cells from the same gland.

Figure 4

Relative fluorescence against time (s). Cells from control (a) and 24-h ligated glands (b) were stimulated with increasing doses of methacholine (10⁻⁸–10⁻⁶m). Cells were then incubated with ionomycin (iono) and then manganese chloride (Mn²⁺) to elicit the maximum and minimum fluorescence signal. During stimulation by methacholine a biphasic response was seen comprising a peak (1) and plateau (2) phase.

Figure 5

Methacholine-induced salivary flow rates from glands 3 days after the removal of a 24-h ligation experiment (black column) compared with the contralateral control gland (white column). Although the recovered gland was 30% smaller (see Table 1) the secretory output per gram gland wet weight was the same. The flow rates were not statistically different from the control gland flow rates shown in Table 2.