ADRENERGIC MODULATION OF THE BLOOD NEUTROPHILIA INDUCED BY PLATELET-ACTIVATING-FACTOR IN RATS

The involvement of catecholamines in blood neutrophilia observed after administration of platelet activating factor (PAF) to rats was studie d. Intravenous (i.v.) injection of PAF (4 mu g/kg) into naive rats mor e than doubled the number of neutrophils after 1 h. In contrast, PAF f ailed to induce neutrophilia in both adrenalectomized rats and those w hich had their catecholamine stores depleted by reserpine. PAF-induced neutrophilia was not inhibited by the selective antagonism of alpha(1 )- and alpha(2)-adrenoceptors with prazosin and yohimbine, respectivel y. However, pretreatment with the beta-adrenoceptor antagonist, propra nolol, significantly inhibited the phenomenon. Increase in the blood n eutrophil counts was also achieved following the i.v. injection of the beta-agonist, salbutamol (1 mg/kg, i.v.). This response was clearly s ensitive to propranolol but was not modified in rats submitted to adre nalectomy or reserpine pretreatment. The results suggest that the bloo d neutrophilia induced by the i.v. administration of PAF in rats is de pendent on the stimulation of beta-adrenoceptors by catecholamines rel eased from adrenal glands.