The role of histamine in the physiologic alterations of IgE anaphylaxis in the rabbit

The Responses of Pulmonary and Systemic Circulation and Airway to Allergic Mediators in Anesthetized Rats

Lung allergic diseases sometimes accompany pulmonary vaso- and broncho-constriction. Rats are currently used for the experimental study of lung allergies. However, their hemodynamic mechanisms are not fully understood. Therefore the effects of allergic mediators were determined systematically in vivo in rats in terms of pulmonary vascular resistance (PVR), airway pressure (AWP) and total peripheral resistance (TPR). We directly measured pulmonary arterial pressure, left atrial pressure, systemic arterial pressure, central venous pressure and aortic blood flow to determine PVR and TPR, as well as AWP, following injections of platelet-activating factor (PAF), histamine, serotonin, leukotriene (LT) C4, and prostaglandin (PG) D2 in anesthetized open-chest artificially ventilated Sprague-Dawley (SD) rats. PVR was dose-dependently increased by consecutive administration of PAF, LTC4, and PGD2, with the maximal responsiveness being PAF>LTC4>PGD2. However, neither histamine nor serotonin changed PVR. TPR was decreased by all agents except LTC4 which actually increased it. PAF and serotonin, but not the other agents, increased AWP. In conclusion, allergic mediators exert non-uniform actions on pulmonary and systemic circulation and airways in anesthetized SD rats: PAF, LTC4 and PGD2, but not histamine or serotonin, caused substantial pulmonary vasoconstriction; LTC4 yielded systemic vasoconstriction, while the others caused systemic vasodilatation; only two mediators, PAF and serotonin, induce airway constriction.

The effects of combined histamine and platelet-activating factor antagonism on systemic anaphylaxis induced by immunoglobulin E in the rabbit

Of the mediators released during IgE-induced allergic reactions, it is not known which have the greatest physiologic import in systemic anaphylactic responses. This study describes the effects of histamine and platelet-activating factor (PAF) antagonism (combined) on IgE-induced systemic anaphylaxis in the rabbit. Pretreatment with 30 mumol/kg chlorpheniramine and 30 mumol/kg cimetidine with (Ch/Ci/WEB group) or without (Ch/Ci group) 2.2 mumol/kg of the PAF antagonist WEB 2086 inhibited the anaphylactic alterations in right ventricular pressure, total pulmonary resistance, and decrease in dynamic compliance but not systemic hypotension. Lethality was inhibited only in the Ch/Ci/WEB group. Because previous studies had shown WEB 2086 alone could inhibit the increase in pulmonary resistance, specificity studies were done to determine if WEB 2086 affected histamine activity or release. Responses to intravenously administered histamine (0.54 mumol/kg) were unaffected by WEB 2086 (13.1 mumol/kg). Also, WEB 2086 did not inhibit in vitro antigen-induced basophil degranulation. Thus, the decrease in dynamic compliance and pulmonary hypertension in IgE anaphylaxis appear to be mediated primarily by histamine and the increase in pulmonary resistance by histamine and/or PAF, whereas lethality appears to involve PAF. Some alterations, most notably systemic hypotension, likely involve other allergic mediators.

Hemodynamic and respiratory effects of thyrotropin-releasing hormone and epinephrine in anaphylactic shock

Thyrotropin-releasing hormone (TRH) has been shown to increase mean arterial pressure during anaphylactic shock. The hemodynamic mechanism of action and the effect of TRH on the respiratory system during anaphylactic shock are not known. A rabbit model of anaphylaxis was used to determine the effect of TRH, epinephrine (EPI), and normal saline (NS) on various cardiovascular and respiratory parameters during anaphylactic shock. Anaphylactic shock was induced by antigen challenge in 31 sensitized animals. After a 25% decrease in mean arterial pressure, they were randomly treated with TRH (2 mg/kg), EPI (0.005 mg/kg), or NS (10 mL/kg). Blood was drawn at baseline and at the end of the experiment for laboratory analysis. Cardiac and respiratory parameters were monitored continuously and measured at baseline, at onset of shock (time zero), and at time intervals for 30 minutes. Animals were treated with repeated doses during the first 15 minutes as needed to maintain mean arterial pressure above shock level. Five of ten TRH-, five of 11 EPI-, and six of ten NS-treated animals survived. The TRH-treated group required fewer doses than the other groups and had increased heart rate, mean arterial pressure, peripheral vascular resistance, respiratory rate, and minute ventilation as well as decreased stroke volume index and lung compliance compared with the NS-treated group. EPI treatment resulted in increased minute ventilation and decreased pulmonary airway resistance compared with NS treatment. The EPI group also had a higher postsurvival epinephrine level than the other groups. No difference in right atrial pressure, cardiac index, acid-base status, pO2, A- a gradient, lung weight, lactate, or norepinephrine levels was found.(ABSTRACT TRUNCATED AT 250 WORDS)

The responsiveness of rabbit bronchial rings to antigen, AGEPC and histamine

Rings of intrapulmonary bronchi isolated from rabbits producing anti-horseradish peroxidase IgE antibodies contracted when exposed to antigen. The contractile response had a lag period of about 1 min, reached a peak at 6 min and then subsided. Bronchi from rabbits with detectable levels of specific IgG (in addition to IgE) antibodies did not differ in response from those with undetectable specific IgG levels. Histamine also contracted rabbit intrapulmonary bronchi with an EC50 of 10 micro (SD 1.29). The response to antigen was completely inhibited with chlorpheniramine (30 microM). In contrast to intrapulmonary bronchi, responsiveness of mainstem bronchi to antigen was observed only occasionally, whereas histamine was equipotent on both mainstem and intrapulmonary bronchi. Thus, the amount of antigen-induced mediator release may be less in the mainstem bronchi. Acetyl glyceryl ether phosphorylcholine, in concentrations up to 10 microM, did not contract either mainstem or intrapulmonary bronchi. This study indicates that histamine is the major mediator of (and acetyl glyceryl ether phosphorylcholine does not significantly participate in) antigen-induced contraction of isolated bronchi from IgE-producing rabbits. The results provide a likely mechanism for the increase in pulmonary resistance observed in IgE anaphylaxis in this species.