Participation of nitric oxide in the sympathetic response to anaphylactic hypotension in anesthetized dogs

Effect of Nitric Oxide Pathway Inhibition on the Evolution of Anaphylactic Shock in Animal Models: A Systematic Review

Simple Summary

Anaphylactic shock (AS) is the most serious consequence of anaphylaxis, with life-threatening sequelae including hypovolemia, shock, and arrhythmias. The literature lacks evidence for the effectiveness of interventions other than epinephrine in the acute phase of anaphylaxis. Our objective was to assess, through a systematic review, how inhibition of nitric oxide (NO) pathways affects blood pressure, and whether such blockade improves survival in AS animal models. AS was induced in all included studies after or before drug administration that targeted blockade of the NO pathway. In all animal species studied, the induction of AS caused a reduction in arterial blood pressure. However, the results show different responses to the inhibition of nitric oxide pathways. Overall, seven of fourteen studies using inhibition of nitric oxide pathways as pre-treatment before induction of AS showed improvement of survival and/or blood pressure. Four post-treatment studies from eight also showed positive outcomes. This review did not find strong evidence to propose modulation of blockade of the NO/cGMP pathway as a definitive treatment for AS in humans. Well-designed in vivo AS animal pharmacological models are needed to explore the other pathways involved, supporting the concept of pharmacological modulation.

Abstract

Nitric oxide (NO) induces vasodilation in various types of shock. The effect of pharmacological modulation of the NO pathway in anaphylactic shock (AS) remains poorly understood. Our objective was to assess, through a systematic review, whether inhibition of NO pathways (INOP) was beneficial for the prevention and/or treatment of AS. A predesigned protocol for this systematic review was published in PROSPERO (CRD42019132273). A systematic literature search was conducted till March 2022 in the electronic databases PubMed, EMBASE, Scopus, Cochrane and Web of Science. Heterogeneity of the studies did not allow meta-analysis. Nine hundred ninety unique studies were identified. Of 135 studies screened in full text, 17 were included in the review. Among six inhibitors of NO pathways identified, four blocked NO synthase activity and two blocked guanylate cyclase downstream activity. Pre-treatment was used in nine studies and post-treatment in three studies. Five studies included both pre-treatment and post-treatment models. Overall, seven pre-treatment studies from fourteen showed improvement of survival and/or arterial blood pressure. Four post-treatment studies from eight showed positive outcomes. Overall, there was no strong evidence to conclude that isolated blockade of the NO/cGMP pathway is sufficient to prevent or restore anaphylactic hypotension. Further studies are needed to analyze the effect of drug combinations in the treatment of AS.

Mouse Anaphylactic Hypotension Is Characterized by Initial Baroreflex Independent Renal Sympathoinhibition Followed by Sustained Renal Sympathoexcitation

Aim: The hemodynamic response to mouse systemic anaphylaxis is characterized by an initial hypertension followed by sustained hypotension. However, the defense mechanisms of the sympathetic nervous system against this circulatory disturbance is not known. Here, we investigated the renal sympathetic nerve activity (RSNA) response to mouse systemic anaphylaxis, along with the roles of carotid sinus baroreceptor, vagal nerves and the transient receptor potential vanilloid type 1 channel (TRPV1). Methods: Male ovalbumin-sensitized C57BL/6N mice were used under pentobarbital anesthesia. RSNA, systemic arterial pressure (SAP) and heart rate (HR) were continuously measured for 60 min after the antigen injection. Results: Within 3 min after antigen injection, RSNA decreased along with a transient increase in SAP. Thereafter, RSNA showed a progressive increase during sustained hypotension. In contrast, HR continuously increased. Sinoaortic denervation, but not vagotomy, significantly attenuated the renal sympathoexcitation and tachycardia from 30 and 46 min, respectively, after antigen. The responses of RSNA, SAP and HR to anaphylaxis were not affected by pretreatment with a TRPV1 inhibitor, capsazepine, or by genetic knockout of TRPV1. Conclusion: The mouse systemic anaphylaxis causes a biphasic RSNA response with an initial baroreflex-independent decrease and secondary increase. The antigen-induced sympathoexcitation and tachycardia at the late stage are partly mediated by carotid sinus baroreceptors. Either vagal nerve or TRPV1 does not play any significant roles in the RSNA and HR responses in anesthetized mice.

Effects of anesthetics on the renal sympathetic response to anaphylactic hypotension in rats

The autonomic nervous system plays an important role in rat anaphylactic hypotension. It is well known that sympathetic nerve activity and cardiovascular function are affected by anesthetics. However, the effects of different types of anesthesia on the efferent renal sympathetic nerve activity (RSNA) during anaphylactic hypotension remain unknown. Therefore, we determined the renal sympathetic responses to anaphylactic hypotension in anesthetized and conscious rats and the roles of baroreceptors in these responses. Sprague-Dawley rats were randomly allocated to anesthetic groups that were given pentobarbital, urethane, or ketamine-xylazine and to a conscious group. The rats were sensitized using subcutaneously injected ovalbumin. The systemic arterial pressure (SAP), RSNA and heart rate (HR) were measured. The effects of sinoaortic baroreceptor denervation on RSNA during anaphylaxis were determined in pentobarbital-anesthetized and conscious rats. In all of the sensitized rats, the RSNA increased and SAP decreased after antigen injection. At the early phase within 35 min of the antigen injection, the antigen-induced sympathoexcitation in the conscious rats was significantly greater than that in the anesthetized rats. Anaphylactic hypotension was attenuated in the conscious rats compared to the anesthetized rats. The anesthetic-induced suppression of SAP and RSNA was greater in the order ketamine-xylazine >urethane = pentobarbital. Indeed, in the rats treated with ketamine-xylazine, RSNA did not increase until 40 min, and SAP remained at low levels after the antigen injection. The baroreceptor reflex, as evaluated by increases in RSNA and HR in response to the decrease in SAP induced by sodium nitroprusside (SNP), was suppressed in the anesthetized rats compared with the conscious rats. Consistent with this finding, baroreceptor denervation attenuated the excitatory responses of RSNA to anaphylaxis in the conscious rats but not in the pentobarbital-anesthetized rats. RSNA was increased markedly in conscious rats during anaphylactic hypotension. Anesthetics attenuated this antigen-induced renal sympathoexcitation through the suppression of baroreceptor function.

N(G)-nitro-L-arginine methyl ester, but not methylene blue, attenuates anaphylactic hypotension in anesthetized mice

To clarify the role of NO in mouse anaphylactic hypotension, effects of a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), on antigen-induced hypotension and portal hypertension were determined in anesthetized BALB/c mice. Systemic arterial pressure (Psa), central venous pressure (Pcv), and portal venous pressure (Ppv) were directly and simultaneously measured. Mice were first sensitized with ovalbumin, and then the injection of antigen was used to decrease Psa and increase Ppv. Pretreatment with L-NAME (1 mg/kg) attenuated this antigen-induced systemic hypotension, but not the increase in Ppv. The effect of inhibitors of soluble guanylate cyclase on anaphylactic hypotension were studied with either methylene blue (3.0 mg/kg) or 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10 mg/kg). Neither modulated any antigen-induced changes. Furthermore, methylene blue did not improve systemic hypotension induced by Compound 48/80 (4.5 mg/kg), a mast cell degranulator, which can produce non-immunological anaphylactoid reactions. These data show in anesthetized BALB/c mice that L-NAME attenuated anaphylactic hypotension without affecting portal hypertension. This beneficial effect of L-NAME appears not to depend on the soluble guanylate cyclase pathway.

Renal sympathetic and cardiac changes associated with anaphylactic hypotension

Severe anaphylactic reactions can result in life-threatening hypotension, but little is known about the autonomic changes that accompany the hypotensive response. The aim of this study was to determine the renal sympathetic and cardiac responses to anaphylactic hypotension, and to evaluate the contribution of sinoaortic and vagal afferent inputs in producing these responses. Rats were sensitized with bovine serum albumin (BSA) and, after 10-14 days, were anaesthesized with sodium pentobarbitone and arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded. In about two thirds of the rats, injection of BSA evoked a severe and sustained hypotension, while in the remainder, there was either a more transient hypotension or else no significant change in arterial pressure. In control unsensitized rats, BSA injection had no significant effect on arterial pressure, heart rate, or RSNA. The BSA-induced hypotension in sensitized rats was associated with increases in HR and RSNA, the magnitudes of which were correlated with the magnitude of the hypotension. There were two components to the cardiac and renal sympathoexcitatory response: (1) an initial increase in HR and RSNA, which immediately followed the onset of hypotension and which was abolished by sinoaortic denervation and vagotomy, and (2) a delayed and gradual increase in HR and RSNA, which continued even while the arterial pressure was recovering and was reduced but not abolished by sinoaortic denervation and vagotomy. Thus, BSA-induced anaphylactic hypotension causes prolonged tachycardia and renal sympathoexcitation, which is only partly due to reflex effects arising from sinoaortic baroreceptors and cardiopulmonary receptors.

NO, but not CO, attenuates anaphylaxis-induced postsinusoidal contraction and congestion in guinea pig liver

The pathophysiology of the hepatic vascular response to anaphylaxis in guinea pig is not known. We studied effects of anaphylaxis on hepatic vascular resistances and liver weight in isolated perfused livers derived from guinea pigs sensitized with ovalbumin. We also determined whether nitric oxide (NO) or carbon monoxide (CO) modulates the hepatic anaphylaxis. The livers were perfused portally and recirculatingly at constant flow with diluted blood. With the use of the double-occlusion technique to estimate the hepatic sinusoidal pressure (Pdo), portal venous resistance (Rpv) and hepatic venous resistance (Rhv) were calculated. An antigen injection caused venoconstriction characterized by an increase in Rpv greater than Rhv and was accompanied by a large liver weight gain. Pretreatment with the NO synthase inhibitor NG-nitro-l-arginine methyl ester, but not the heme oxygenase inhibitor zinc protoporphyrin IX, potentiated the antigen-induced venoconstriction by increasing both Rpv and Rhv (2.2- and 1.2-fold increase, respectively). In conclusion, anaphylaxis causes both pre- and postsinusoidal constriction in isolated guinea pig livers. However, the increases in postsinusoidal resistance and Pdo cause hepatic congestion. Endogenously produced NO, but not CO, modulates these responses.