LPS‐induced blood neutrophilia is inhibited by α1‐adrenoceptor antagonists: a role for catecholamines

A role for catecholamines in the regulation of the blood neutrophilia induced by intravenous (i.v.) injection of lipopolysaccharide (LPS; 250 μg/kg) was examined in Wistar rats by means of surgical adrenalectomy or pretreatment with adrenergic and dopaminergic antagonists into naive animals. Treatment of animals with a single dose (250 μg/kg) of LPS caused a dramatic increase in the number of circulating neutrophils concomitant with a decrease in the number of these cells in the bone marrow. These effects were partially reversed when catecholamine stores were depleted with reserpine. It was found that neither adrenalectomy nor pretreatment with the dopaminergic antagonists, chlorpromazine and pimozide, affected the changes in neutrophil counts induced by LPS. The injection of the α1/α2‐adrenoceptor antagonist, phentolamine, and the selective α1‐adrenoceptor antagonist, prazosin, significantly decreased blood neutrophilia induced by LPS. However, neither the selective (α2‐adrenoceptor antagonist, yohimbine, nor the β‐adrenoceptor antagonist, propranolol, had any effect on LPS response. Taken together, these findings support the hypothesis that the catecholamine norepinephrine plays a role in the regulation of the LPS‐induced neutrophilia through activation of α1‐adrenoceptors. J. Leukoc. Biol. 61: 689‐694; 1997.