Dexamethasone and thyroid hormone pretreatment upregulate alveolar epithelial fluid clearance in adult rats

The in vivo effect of 48-h glucocorticoid and thyroid hormone 3,3′,5-triiodine-l-thyronine (T3) pretreatment on alveolar epithelial fluid transport was studied in adult rats. An isosmolar 5% albumin solution was instilled, and alveolar fluid clearance was studied for 1 h. Compared with controls, dexamethasone pretreatment increased alveolar fluid clearance by 80%. T3 pretreatment stimulated alveolar fluid clearance by 65%, and dexamethasone and T3 had additive effects (132%). Propranolol did not inhibit alveolar fluid clearance in either group, indicating that stimulation was not secondary to endogenous β-adrenergic stimulation. With the use of bromodeoxyuridine in vivo labeling, there was no evidence of cell proliferation. Alveolar fluid clearance was partially inhibited by amiloride in all groups. Fractional amiloride inhibition was greater in dexamethasone- and dexamethasone-plus-T3-pretreated rats than in control animals, but less in T3-pretreated rats. In summary, pretreatment with dexamethasone, T3, or both in combination upregulate in vivo alveolar fluid clearance similarly to short-term β-adrenergic stimulation. The effects are mediated partly by increased amiloride-sensitive Na+ transport, because the stimulated alveolar fluid clearance was more amiloride sensitive than in control rats. These observations may have clinical relevance because glucocorticoid therapy is commonly used with acute lung injury.