Hyperosmolar Solutions Stimulate Mucus Secretion in the Ferret Trachea: Evaluation of Secretory Pathways

Hyperosmolar Solutions Stimulate Mucus Secretion in the Ferret Trachea: Evaluation of Secretory PathwaysThere was 47% increase in lysozyme secretion with exposure to 3.69 g/dL of saline solution and a 54% increase with exposure to 10.69 g/dL of saline solution (each n = 5, p < 0.05) compared with exposure to KHS (Fig 2). The amounts of lysozyme secretion in tracheae exposed to KHS, 3.69 g/dL of saline solution, and 10.69 g/dL of saline solution were 3.19 ± 0.38 ^g/g, 4.58 ± 0.37 ^g/g, and 4.68 ± 0.27 ^g/g, respectively. The calculated ratio of mucin to lysozyme secretion was 2.0 in isotonic solution (KHS) as well as in 3% saline solution and 10% saline solution, suggesting that osmolar challenge induces a similar degree of secretion from mucous and serous glands.
The Kinetics of 3.69 g/dL Saline Solution-Induced Mucin Secretion
Tracheal segments were immersed in 3.69 g/dL of saline solution (1,192 mOsm) or KHS, and the buffers were collected at 5, 10, 15, and 30 min after incubation. Mucin secretion was induced immediately, and rapidly reached a maximum (Fig 3).
Hyperosmolar Solution Stimulates Mucin Secretion Only via the Luminal Side
Mucin secretion was stimulated only when the luminal side of the intact trachea was incubated with 1.69 g/dL of saline solution (597 mOsm/L), and the degree of stimulation was the same as when both the outside and the luminal side of the trachea were exposed (Fig 4).
Hyperosmolar saline solution-induced mucin and lysozyme secretion was not significantly inhibited by 104 mol/L of atropine, proteinase inhibitors, or 105 mol/L of NDGA (Fig 5). so

Discussion
Hyperosmolar inhalation produces a dose-dependent increase in mucin secretion in the cat trachea and in the human nose. Our results are consistent with these studies, showing that hyperosmolar saline solution or mannitol induced mucin secretion in a dose-related fashion.
Fig2
Figure 2. The effect of 3.69 g/dL and 10.69 g/dL saline solutions on lysozyme secretion. There was a 47% and 54% increase in lysozyme secretion after exposure to 3% and 10% saline solution, respectively (n = 5). Data are mean ± SEM for 3.69 g/dL and 10.69 g/dL saline solutions (p < 0.05), as compared to KHS-treated group (analysis of variance Scheffe F test).
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Figure 3. Kinetics of mucin secretion after exposure to 3.69 g/dL of saline solution. The segments were immersed 3.69 g/dL (1,192 mOsm/L) in saline solution or KHS (288 mOsm/L) [each group, n = 16], and the solution was collected for mucin analysis 5, 10, 15, and 30 min after incubation. Data are mean ± SEM. *p < 0.0001, compared to KHS-treated group (Mann Whitney U test).
Fig4
Figure 4. Hyperosmolar solution-stimulated mucin secretion via the epithelial surface. Saline solution (1.69 g/dL, 597 mOsm/L) or KHS (0.69 g/dL NaCl, 288 mOsm/L) was added into the inside of a whole trachea, and both ends of the trachea were tied. These tied tracheae (n = 2 each) were incubated for 20 min at 38°C with 1.69 g/dL of saline solution or KHS, as follows: (1) inside saline-outside KHS, (2) outside saline-inside KHS, or (3) control, inside and outside KHS. After a 20-min exposure, the inside solutions were collected and mucin was measured. Group 2 was significantly different (p < 0.05) from group 1 and group 3.
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Figure 5. Effect of inhibitors of mucin secretion on osmolar-induced secretion. Tracheal segments were incubated for 20 min with each individual inhibitor in KHS or in only KHS (period 1), and then incubated for another 20 min in 3.69 g/dL (1,193 mOsm/L) in saline solution alone (positive control), with saline solution and each inhibitor in KHS, or with only KHS (negative control) [period 2]. Mucin secretion per gram of tissue during period 2 is shown. Inhibitors used were atropine at 104 mol/L, NDGA at 105 as an inhibitor of arachidonic acid metabolites, and a protease inhibitor cocktail (PIC) containing phenylmethylsulfonyl fluoride as an inhibitor of serine protease, leupeptin as a nonspecific protease inhibitor, and pepstatin A as an acid protease inhibitor. Error bars = SEM; p = not significant.

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