Effects of β-adrenoceptor antagonists on anaphylactic hypotension in conscious rats

Angiopoietin-2 is released during anaphylactic hypotension in anesthetized and unanesthetized rats

Angiopoietin (Angpt)-2, a permeability-increasing growth factor, is involved in vascular leakage of sepsis and acute lung injury, and could be released from endothelium in response to anaphylaxis-related secretagogues such as histamine and leukotrienes, or cytokines. However, roles of Angpt-2 in the hyperpermeability during systemic anaphylaxis are not known. Thus, we determined plasma levels of Angpt-2 and cytokines and vascular permeability during anaphylactic hypotension in unanesthetized rats. Anaphylaxis was induced by an intravenous injection of ovalbumin antigen. Mean arterial blood pressure (MBP) was measured, and hematocrit (Hct) and plasma levels of Angpt-2 and cytokines were assessed for 24 h after antigen injection. Separately, vascular permeability was measured in various organs using the Evans blue dye method, and Angpt-2 mRNA expression in liver was measured. After antigen injection, MBP decreased to the nadir at 6 min, and returned to baseline at 45 min, and Hct peaked at 20 min and thereafter progressively declined, suggesting that vascular leak and hypotension occurred within 20 min. Plasma Angpt-2 levels began to increase significantly at 1 h after antigen, reaching the peak 2.7-fold baseline at 6 h with a return to baseline at 24 h. Detected cytokines of IL-1α, IL-1β, IL-6, IL-10, and TNF-α peaked 1 or 2 h after antigen. Angpt-2 mRNA increased at 2 h and showed an increasing tendency at 6 h. Vascular permeability in bronchus, trachea, intestines, mesentery and skeletal muscle was increased at 10 min but not at 6 h after antigen. In addition, we confirmed using anesthetized rat anaphylaxis models that plasma Angpt-2 levels increased at 1 h after antigen. In conclusion, plasma Angpt-2 is elevated presumably due to increased cytokines and enhanced gene transcription during anaphylaxis in anesthetized and unanesthetized rats.

Effects of β-adrenoceptor activation on haemodynamics during hypoxic stress in rats

NEW FINDINGS

What is the central question of this study? The acute hypoxic compensatory reaction is based on haemodynamic changes, and β-adrenoceptors are involved in haemodynamic regulation. What is the role of β-adrenoceptors in haemodynamics during hypoxic exposure? What is the main finding and its importance? Activation of β₂ -adrenoceptors attenuates the increase in pulmonary artery pressure during hypoxic exposure. This compensatory reaction activated by β₂ -adrenoceptors during hypoxic stress is very important to maintain the activities of normal life.

ABSTRACT

The acute hypoxic compensatory reaction is accompanied by haemodynamic changes. We monitored the haemodynamic changes in rats undergoing acute hypoxic stress and applied antagonists of β-adrenoceptor (β-ARs) subtypes to reveal the regulatory role of β-ARs on haemodynamics. Sprague-Dawley rats were randomly divided into control, atenolol (β₁ -AR antagonist), ICI 118,551 (β₂ -AR antagonist) and propranolol (non-selective β-AR antagonist) groups. Rats were continuously recorded for changes in haemodynamic indexes for 10 min after administration. Then, a hypoxic ventilation experiment [15% O₂ , 2200 m a.sl., 582 mmHg (0.765 Pa), P O 2 87.3 mmHg; Xining, China] was conducted, and the indexes were monitored for 5 min after induction of hypoxia. Plasma catecholamine concentrations were also measured. We found that, during normoxia, the mean arterial pressure, heart rate, ascending aortic blood flow and pulmonary artery pressure were reduced in the propranolol and atenolol groups. Catecholamine concentrations were increased significantly in the atenolol group compared with the control group. During hypoxia, mean arterial pressure and total peripheral resistance were decreased in the control, propranolol and ICI 118,551 groups. Pulmonary arterial pressure and pulmonary vascular resistance were increased in the propranolol and ICI 118,551 groups. During hypoxia, catecholamine concentrations were increased significantly in the control group, but decreased in β-AR antagonist groups. In conclusion, the β₂ -AR is involved in regulation of pulmonary haemodynamics in the acute hypoxic compensatory reaction, and the activation of β₂ -ARs attenuates the increase in pulmonary arterial pressure during hypoxic stress. This compensatory reaction activated by β₂ -ARs during hypoxic stress is very important to maintain activities of normal life.

The pathophysiology of anaphylaxis

Anaphylaxis is a severe systemic hypersensitivity reaction that is rapid in onset; characterized by life-threatening airway, breathing, and/or circulatory problems; and usually associated with skin and mucosal changes. Because it can be triggered in some persons by minute amounts of antigen (eg, certain foods or single insect stings), anaphylaxis can be considered the most aberrant example of an imbalance between the cost and benefit of an immune response. This review will describe current understanding of the immunopathogenesis and pathophysiology of anaphylaxis, focusing on the roles of IgE and IgG antibodies, immune effector cells, and mediators thought to contribute to examples of the disorder. Evidence from studies of anaphylaxis in human subjects will be discussed, as well as insights gained from analyses of animal models, including mice genetically deficient in the antibodies, antibody receptors, effector cells, or mediators implicated in anaphylaxis and mice that have been "humanized" for some of these elements. We also review possible host factors that might influence the occurrence or severity of anaphylaxis. Finally, we will speculate about anaphylaxis from an evolutionary perspective and argue that, in the context of severe envenomation by arthropods or reptiles, anaphylaxis might even provide a survival advantage.

Use of enoximone in management of anaphylaxis complicated by labetalol use

A 42-year-old woman with end-stage renal failure was admitted to the intensive care unit following resuscitation from a pulseless electrical activity cardiac arrest after intravenous piperacillin/tazobactam. Persistent bradycardia and hypotension, unresponsive to epinephrine and norepinephrine, were suspected to have been exacerbated by chronic labetalol therapy for resistant arterial hypertension. As an alternative, the non-adrenergic inotrope, enoximone, was started. This, combined with thrombolysis for possible pulmonary embolism, heralded significant haemodynamic improvement, allowing weaning from inotropic support. A clear CT pulmonary angiogram 2 days post-arrest and significantly raised mast cell tryptase levels confirmed anaphylaxis rather than pulmonary embolism as the precipitating cause. We believe this to be the first case report of phosphodiesterase-III inhibitor use in the management of anaphylaxis complicated by α/β-blockade, and discuss the mechanism behind this effect and comparison with the more commonly reported use of glucagon.

Blood pressure reduction induced by low dose of epinephrine via different routes in rats

BACKGROUND

Epinephrine was recently shown to induce a hypotension episode. Activation of β₂-adrenoceptors with smooth muscle relaxation may be the underlying mechanism. This study investigated the effects of ICI 118551, a β₂-adrenoceptors antagonist, on epinephrine-induced blood pressure reduction via different administration routes in rats.

METHODS

A total of 144 Sprague Dawley rats were equally randomized into 3 groups (intranasal, intravenous, and intra-arterial administration), each with 4 subgroups: saline + saline, ICI 118551 + saline, saline + epinephrine, and ICI 118551 + epinephrine. All rats were anesthetized while spontaneously breathing. Epinephrine was administered at doses of 5 μg/kg via nose, 0.25 μg/kg via femoral vein, and 0.1 μg/kg via aorta. Mean arterial pressure and heart rate were monitored.

RESULTS

Mean arterial pressure decreased in all 3 saline + epinephrine subgroups after administration (P < 0.05), whereas it did not in other subgroups. Heart rate had no significant change in all subgroups.

CONCLUSIONS

Epinephrine-induced blood pressure reduction can be prevented by ICI 118551 in rats, suggesting that the activation of β₂-adrenoceptors contributes to blood pressure reduction.

Alpha-adrenoceptor antagonists and chemical sympathectomy exacerbate anaphylaxis-induced hypotension, but not portal hypertension, in anesthetized rats

Anaphylactic shock is sometimes life-threatening, and it is accompanied by hepatic venoconstriction in animals, which, in part, accounts for anaphylactic hypotension. Roles of norepinephrine and α-adrenoceptor in anaphylaxis-induced hypotension and portal hypertension were investigated in anesthetized ovalbumin-sensitized Sprague-Dawley rats. The sensitized rats were randomly allocated to the following pretreatment groups (n = 6/group): 1) control (nonpretreatment), 2) α1-adrenoceptor antagonist prazosin, 3) nonselective α-adrenoceptor antagonist phentolamine, 4) 6-hydroxydopamine-induced chemical sympathectomy, and 5) surgical hepatic sympathectomy. Anaphylactic shock was induced by an intravenous injection of the antigen. The systemic arterial pressure (SAP), central venous pressure (CVP), portal venous pressure (PVP), and portal venous blood flow (PBF) were measured, and splanchnic [Rspl: (SAP-PVP)/PBF] and portal venous [Rpv: (PVP-CVP)/PBF] resistances were determined. Separately, we measured efferent hepatic sympathetic nerve activity during anaphylaxis. In the control group, SAP markedly decreased, followed by a gradual recovery toward baseline. PVP and Rpv increased 3.2- and 23.3-fold, respectively, after antigen. Rspl decreased immediately, but only transiently, after antigen, and then increased 1.5-fold later than 10 min. The α-adrenoceptor antagonist pretreatment or chemical sympathectomy inhibited the late increase in Rspl and the SAP recovery. Pretreatment with α-adrenoceptor antagonists, or either chemical or surgical hepatic sympathectomy, did not affect the antigen-induced increase in Rpv. Hepatic sympathetic nerve activity did not significantly change after antigen. In conclusion, α-adrenoceptor antagonists and chemical sympathectomy exacerbate anaphylaxis-induced hypotension, but not portal hypertension, in anesthetized rats. Hepatic sympathetic nerves are not involved in anaphylactic portal hypertension.