Pulmonary platelet accumulation induced by catecholamines: Its involvement in lipopolysaccharide-induced...

Intravenously injected lipopolysaccharides (LPS) rapidly induce pulmonary platelet accumulation (PPA) and anaphylaxis-like shock (ALS) in mice. Macrophages reportedly release catecholamines rapidly upon stimulation with LPS. Here, we examined the involvement of macrophage-derived catecholamines in LPS-induced PPA and ALS. A catecholamine or Klebsiella O3 (KO3) LPS was intravenously injected into mice, with 5-hydroxytryptamine in the lung being measured as a platelet marker. The tested catecholamines induced PPA, leading to shock. Their minimum shock-inducing doses were at the nmol/kg level. The effects of epinephrine and norepinephrine were inhibited by prazosin (α1 antagonist) and by yohimbine (α2 antagonist), while dopamine's were inhibited only by prazosin. Use of synthetic adrenergic α1- and/or α2-agonists, platelet- or macrophage-depleted mice, a complement C5 inhibitor and C5-deficient mice revealed that (a) α2-receptor-mediated PPA and shock depend on both macrophages and complements, while α1-receptor-mediated PPA and shock depend on neither macrophages nor complements, (b) the PPA and ALS induced by KO3-LPS depend on α1- and α2-receptors, macrophages, and complements, and (c) KO3-LPS-induced PPA is preceded by catecholamines decreasing in serum. Together, these results suggest the following. (i) Catecholamines may stimulate macrophages and release complement C5 via α2-receptors. (ii) Macrophage-derived catecholamines may mediate LPS-induced PPA and ALS. (iii) Moderate PPA may serve as a defense mechanism to remove excess catecholamines from the circulation by promoting their rapid uptake, thus preventing excessive systemic effects. (iv) The present findings might provide an insight into possible future pharmacological strategies against such diseases as shock and acute respiratory distress syndrome.