EFFECTS OF DEXAMETHASONE IN A MODEL OF LUNG HYPERRESPONSIVENESS IN THE RAT

In rats, Sephadex treatment on days 0, 2 and either 4 or 5 resulted in a blood and lung eosinophilia, an increase in lung cell fragility, an increase in the functional activity of peritoneal eosinophils in vitr o and a sustained increased responsiveness of lung parenchymal strips to KCl, 5-hydroxytryptamine (5-HT) and carbachol that was not associat ed with oedema or gross fibrosis. The corticosteroid dexamethasone, wh en given before each injection of Sephadex, reduced all these effects of Sephadex. When given 30 min after the last injection of Sephadex, d examethasone had no effect on the number of blood and lung eosinophils but it did reduce the functional activity of peritoneal eosinophils, the increased lung cell fragility and the hyperresponsivness to 5-HT. Repeated administration of dexamethasone to rats with an established h yperresponsiveness that was no longer associated with cellular inflamm ation had minimal effects on this hyperresponsiveness.