A role for adrenoceptors in the regulation of pleural neutrophilia induced by LPS

The role of catecholamines in regulating pleural neutrophilia evoked by intrathoracic (i.t.) injection of lipopolysaccharide (LPS) was investigated in Wistar rats by means of surgical adrenalectomy, depletion of catecholamine stores or adrenoceptor blockade. Treatment of animals with a single dose of LPS evoked a dramatic increase in the number of pleural neutrophils concomitant with an increase in the number of these cells in blood at 4 h. Although blood neutrophilia was drastically reduced when catecholamine stores were depleted with intraperitoneal (i.p.) injection of reserpine, pleural neutrophilia was not modified. However, the i.t. injection of reserpine reduced the increase in pleural neutrophils after LPS stimulation. Adrenalectomy failed to inhibit the increase in neutrophil counts in the blood or pleural cavity after LPS challenge. Pretreatment with intravenous (i.v.) injection of prazosin, an α 1/α 2B antagonist, reduced LPS-induced blood but not pleural neutrophilia. On the other hand, although pleural neutrophilia was not affected by systemic pretreatment with the α 2-adrenoceptor antagonist, yohimbine, the local treatment (i.t. injection) with this antagonist markedly reduced the increase in pleural neutrophil counts observed after stimulation by LPS. In contrast, pleural neutrophilia induced by i.t injection of formyl-methionyl-leucyl-phenylalanine (fMLP) was not modified by local treatment with yohimbine. Taken together, our results suggest that catecholamines, through activation of α 1 and α 2-adrenoceptors, play a role in the regulation of blood and pleural neutrophilia observed during the inflammatory response evoked by LPS in the pleural cavity.