Mucous solids and liquid secretion by airways: studies with normal pig, cystic fibrosis human, and non-cystic fibrosis human bronchi.

To better understand how airways produce thick airway mucus, nonvolatile solids were measured in liquid secreted by bronchi from normal pig, cystic fibrosis (CF) human, and non-CF human lungs. Bronchi were exposed to various secretagogues and anion secretion inhibitors to induce a range of liquid volume secretion rates. In all three groups, the relationship of solids concentration (percent nonvolatile solids) to liquid volume secretion rate was curvilinear, with higher solids concentration associated with lower rates of liquid volume secretion. In contrast, the secretion rates of solids mass and water mass as functions of liquid volume secretion rates exhibited positive linear correlations. The y-intercepts of the solids mass-liquid volume secretion relationships for all three groups were positive, thus accounting for the higher solids concentrations in airway liquid at low rates of secretion. Predictive models derived from the solids mass and water mass linear equations fit the experimental percent solids data for the three groups. The ratio of solids mass secretion to liquid volume secretion was 5.2 and 2.4 times higher for CF bronchi than for pig and non-CF bronchi, respectively. These results indicate that normal pig, non-CF human, and CF human bronchi produce a high-percent-solids mucus (>8%) at low rates of liquid volume secretion (≤1.0 µl·cm(-2)·h(-1)). However, CF bronchi produce mucus with twice the percent solids (~8%) of pig or non-CF human bronchi at liquid volume secretion rates ≥4.0 µl·cm(-2)·h(-1).

Effects of secretagogues on net and unidirectional liquid fluxes across porcine bronchial airways.

Rates of liquid secretion and absorption across the bronchopulmonary airways are important for regulating airway surface liquid volume and maintaining mucociliary transport. The current study demonstrates the feasibility of measuring not just net liquid movements but unidirectional liquid movements across isolated intact bronchi from swine. Airways were liquid filled to assess both net liquid movements, and, in the presence of NPPB to selectively inhibit secretion, unidirectional absorption. Unidirectional liquid secretion rates were determined by subtraction. For comparison, net liquid movements were assessed in air-filled airways in parallel. In the absence of secretagogues, unidirectional absorption was observed (4.63 +/- 0.53 microl.cm(-2).h(-1)) with little unidirectional secretion (1.42 +/- 0.36 microl.cm(-2).h(-1)). ACh, substance P (SP), and vasoactive intestinal peptide (VIP) all induced unidirectional secretion (10.64 +/- 1.52 microl.cm(-2).h(-1), 14.16 +/- 1.39 microl.cm(-2).h(-1), and 4.25 +/- 0.25 microl.cm(-2).h(-1), respectively) without affecting unidirectional absorption. Net liquid secretion in air-filled airways was close to that in liquid-filled airways except with VIP. VIP induced net secretion in air-filled airways (4.44 +/- 1.26 microl.cm(-2).h(-1)), but negligible net change in liquid movement occurred in liquid-filled airways. This effect was likely to have been caused by the higher solid content of the VIP-induced mucous liquid (3.98 +/- 0.26%) compared with the ACh- and SP-induced liquid (2.06 +/- 0.07% and 2.15 +/- 0.07%, respectively). We conclude that this technique allows important quantitative distinctions to be made between liquid secretion and absorption in intact bronchial airways.