Liquid movement and electrical potential difference across in vitro lungs from fetal guinea pigs : responses to expansion and related factors

Lungs from near-term fetal guinea pigs were supported in vitro; lung liquid production was measured by a dye dilution method using Blue Dextran 2000; electrical potential difference (PD) across fetal airways was measured using KCl-Agar salt bridges. Untreated (control) preparations produced fluid for three hours with no significant change in rate; unstimulated PD was -7.5 ± 0.4 mV (lumen -ve). 70% expansion with Krebs-Henseleit (K-H) saline decreased fluid production (53.5 ± 6.6%) in preparations from small fetuses (<100 g) and caused fluid reabsorption (124.8 ± 12.1%) in preparations from large fetuses (>100 g). Expansion did not cause any detectable change in bronchial PD. Glucose concentration in lung liquid (0.19 ± 0.03 mM) was lower than that of fetal plasma (1.35 ± 0.11 mM). The use of 0.9% NaCl as expansion fluid, to minimize possible effects of intraluminal glucose, had no effect on the response to expansion, and intraluminal instillation of amiloride (10⁻⁶ M or 10⁻⁵ M) did not reduce expansion-induced reabsorption significantly. Neither the β-adrenergic antagonist propranolol (10⁻⁷ M) nor the a antagonist phentolamine (10⁻⁵ M) inhibited fluid reabsorption following expansion. Untreated control preparations, incubated in pairs, showed no significant changes in fluid production throughout incubation. When one preparation was expanded by 70% with K - H saline, the expanded preparation reabsorbed fluid (125.4 ± 42.6%), and the unexpanded companion lungs reduced fluid production (88.2 ± 10.7%). This suggested the release of an active agent by expanded lungs. Amiloride (10⁻⁶ M) or propranolol (10⁻⁷ M) reduced the effects in unexpanded companion lungs but not in expanded preparations. Lung liquid norepinephrine concentration was 97.0 ± 12.0 nM (n = 6) and increased to 190.0 ± 17.0 nM after 70% expansion; the concentration in the bathing saline was 1.5 ± 0.2 nM and did not increase significantly. Exogenous epinephrine (2.2 x 10⁻⁶ M) and norepinephrine (10⁻⁵ M) caused strong fluid reabsorptions (146.2 ± 23.7% and 137 ± 21.7% respectively). Intraluminal amiloride (10⁻⁵ M) or 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, CI" channel blocker, 10⁻⁵ M) did not reduce effects of norepinephrine. Epinephrine (10⁻⁷ M) reduced bronchial PD by 27.4 ± 2.4% whereas norepinephrine (10⁻⁶ M) reduced it by 31.4 ± 3.7%. Propranolol (10⁻⁷ M) abolished these changes in PD while phentolamine (10⁻⁵ M), amiloride (10⁻⁴ M) or N-phenylanthrilic acid (DPC, 10⁻⁴ M) did not. A low level of somatostatin-like immunoreactivity was detected in the bathing saline; it did not increase with expansion. Although PGE₂ was not detected in the bathing saline, indomethacin (1.5 x 10⁻⁵ M) reduced responses of unexpanded companion lungs. Exogenous prostaglandins had the following effects: PGF₂a (5 x 10⁻⁷ M) caused fluid reabsorption (130.8 ± 48.5%); P G E 2 (10⁻⁶ M) halted fluid production (95.2 ± 26.2%) and reduced bronchial PD (33.6 + 7.5%); PGD₂ (10⁻⁶ M) reduced production (51.4 ± 13.3%), and PGI₂ (10⁻⁶ M) was without effect. The calcium ionophore, A23187 (10⁻⁵ M) halted fluid production in the hour of application (95.0 ± 8.3% fall) and caused reabsorption in the final hour (140.5 ± 15.8%); Calcium-mediated secretagogues, histamine (10⁻⁶ M) and bradykinin (10⁻⁸ M and 10⁻⁷ M) had lesser but equally long-lasting effects. The histamine antagonist, mianserin, did not reduce effects of the unexpanded companion lungs significantly.Science, Faculty ofZoology, Department ofGraduat