Yuhichi Kuda

Pulmonary vasoconstrictive and bronchoconstrictive responses to anaphylaxis are weakened via β2-adrenoceptor activation by endogenous epinephrine in anesthetized rats.

Background:Patients treated with propranolol, a nonselective &bgr;-adrenoceptor antagonist, have increased incidence and severity of anaphylaxis. We determined whether &bgr;1- or &bgr;2-adrenoceptor antagonist modulated pulmonary vasoconstriction and bronchoconstriction in rat anaphylactic hypotension. Methods:Anesthetized ovalbumin-sensitized male Sprague-Dawley rats were randomly allocated to the following pretreatment groups (n = 7/group): (1) sensitized control (nonpretreatment), (2) propranolol, (3) the selective &bgr;2-adrenoceptor antagonist ICI 118,551, (4) the selective &bgr;1-adrenoceptor antagonist atenolol, and (5) adrenalectomy. Shock was induced by an intravenous injection of the antigen. Mean arterial pressure, pulmonary arterial pressure, left atrial pressure, central venous pressure, portal venous pressure, airway pressure, and aortic blood flow were continuously measured. Results:In either sensitized control or atenolol-pretreated rats, mean arterial pressure and aortic blood flow decreased substantially, whereas pulmonary arterial pressure and airway pressure did not increase soon after antigen injection. In contrast, in rats pretreated with either propranolol, ICI 118,551, or adrenalectomy, airway pressure significantly increased by 14 cm H2O, and pulmonary arterial pressure by 7.5 mmHg after antigen injection. At 2.5 min after antigen injection, the plasma concentration of epinephrine increased 14-fold in the sensitized rats except for the adrenalectomy group. Portal venous pressure after antigen injection increased by 16 mmHg similarly in all sensitized rats. All of the sensitized control group and two of the atenolol group were alive for 60 min after antigen injection, whereas all rats of the propranolol, ICI 118,551, and adrenalectomy groups died within 50 min after antigen injection. Conclusions:The pulmonary vasoconstrictive and bronchoconstrictive responses to systemic anaphylaxis were weakened via &bgr;2-adrenoceptor activation by epinephrine endogenously released from the adrenal gland in the anesthetized Sprague-Dawley rats.

Hypothalamic nesfatin-1 stimulates sympathetic nerve activity via hypothalamic ERK signaling

Nesfatin-1 acts on the hypothalamus and regulates the autonomic nervous system. However, the hypothalamic mechanisms of nesfatin-1 on the autonomic nervous system are not well understood. In this study, we found that intracerebroventricular (ICV) administration of nesfatin-1 increased the extracellular signal–regulated kinase (ERK) activity in rats. Furthermore, the activity of sympathetic nerves, in the kidneys, liver, and white adipose tissue (WAT), and blood pressure was stimulated by the ICV injection of nesfatin-1, and these effects were abolished owing to pharmacological inhibition of ERK. Renal sympathoexcitatory and hypertensive effects were also observed with nesfatin-1 microinjection into the paraventricular hypothalamic nucleus (PVN). Moreover, nesfatin-1 increased the number of phospho (p)-ERK1/2–positive neurons in the PVN and coexpression of the protein in neurons expressing corticotropin-releasing hormone (CRH). Pharmacological blockade of CRH signaling inhibited renal sympathetic and hypertensive responses to nesfatin-1. Finally, sympathetic stimulation of WAT and increased p-ERK1/2 levels in response to nesfatin-1 were preserved in obese animals such as rats that were fed a high-fat diet and leptin receptor-deficient Zucker fatty rats. These findings indicate that nesfatin-1 regulates the autonomic nervous system through ERK signaling in PVN-CRH neurons to maintain cardiovascular function and that the antiobesity effect of nesfatin-1 is mediated by hypothalamic ERK-dependent sympathoexcitation in obese animals.

Mouse anaphylactic shock is caused by reduced cardiac output, but not by systemic vasodilatation or pulmonary vasoconstriction, via PAF and histamine

AIMS Systemic anaphylaxis is life-threatening, and its pathophysiology is not fully clarified. Mice are frequently used for experimental study on anaphylaxis. However, the hemodynamic features and mechanisms of mouse anaphylactic hypotension remain unknown. Therefore, we determined mechanisms of systemic and pulmonary vascular response to anaphylactic hypotension in anesthetized BALB/c mice by using receptor antagonists of chemical mediators. MAIN METHODS Anaphylaxis was actively induced by an intravenous injection of the ovalbumin antigen into open-chest artificially ventilated sensitized mice. Mean arterial pressure (MAP), pulmonary arterial pressure (PAP), left atrial pressure, central venous pressure, and aortic blood flow (ABF) were continuously measured. KEY FINDINGS In sensitized control mice, MAP and ABF showed initial, transient increases, followed by progressive decreases after the antigen injection. Total peripheral resistance (TPR) did not decrease, while PAP initially and transiently increased to 18.5±0.5mmHg and pulmonary vascular resistance (PVR) also significantly increased. The antigen-induced decreases in MAP and ABF were attenuated by pretreatment with either a platelet-activating factor (PAF) receptor antagonist, CV6209, or a histamine H1 receptor antagonist, diphenhydramine, and were abolished by their combination. Diphenhydramine augmented the initial increases in PAP and PVR, but did not affect the decrease of the corresponding MAP fall. The antagonists of either leukotriene C4 or serotonin, alone or in combination with CV6209, exerted no significant effects. SIGNIFICANCE Mouse anaphylactic hypotension is caused by a decrease in cardiac output but not vasodilatation, via actions of PAF and histamine. The slight increase in PAP is not involved in mouse anaphylactic hypotension.

The Role of Lumbar Sympathetic Nerves in Regulation of Blood Flow to Skeletal Muscle during Anaphylactic Hypotension in Anesthetized Rats

During hypovolemic shock, skeletal muscle blood flow could be redistributed to vital organs via vasoconstriction in part evoked by activation of the innervating sympathetic nerve activity. However, it is not well known whether this mechanism operates during anaphylactic shock. We determined the femoral artery blood flow (FBF) and lumbar sympathetic nerve activity (LSNA) mainly regulating the hindquater muscle blood flow during anaphylactic hypotension in anesthetized rats. Anesthetized Sprague-Dawley rats were randomly allocated to the following groups (n = 7/group): (1) non-sensitized, (2) anaphylaxis, (3) anaphylaxis-lumbar sympathectomy (LS) and (4) anaphylaxis-sinoaortic denervation (SAD) groups. Anaphylaxis was induced by an intravenous injection of the ovalbumin antigen to the sensitized rats. The systemic arterial pressure (SAP), heart rate (HR), central venous pressure (CVP), FBF and LSNA were continuously measured. In the anaphylaxis group, LSNA and HR increased, while SAP and FBF decreased after antigen injection. In the anaphylaxis-SAD group, LSNA did not significantly change during the early phase, but the responses of SAP and FBF were similar to those in the anaphylaxis group. In the anaphylaxis-LS group, both FBF and SAP decreased similarly to the anaphylaxis group during anaphylactic hypotension. These results indicated that LSNA increased via baroreceptor reflex, but this sympathoexcitation or LS did not affect antigen-induced decreases in FBF or SAP. Lumbar sympathetic nerves are not involved in regulation of the blood flow to the hindlimb or systemic blood pressure during anaphylactic hypotension in anesthetized rats.

Angiotensin II and vasopressin are involved in the defense system against anaphylactic hypotension in anesthetized rats

Anaphylactic shock is sometimes life-threatening, but the defense system against this circulatory failure was not fully understood. Ameliorating roles of angiotensin (ANG) II and vasopressin in anaphylactic hypotension were investigated in anesthetized ovalbumin-sensitized Sprague-Dawley rats. The sensitized rats were randomly allocated to the following pretreatment groups (n=7/group): (1) control (non-pretreatment), (2) ANG II synthesis inhibitor captopril, (3) ANG II receptor antagonist losartan, and (4) V1a vasopressin receptor antagonist. 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 vascular resistance (Rspl: (SAP-PVP)/PBF) was determined. In the control group, SAP markedly decreased, followed by a gradual recovery toward baseline. Rspl transiently decreased immediately after antigen, and then increased 1.5-fold at 15 min and thereafter. The pretreatment with either losartan, captopril or V1a receptor antagonist augmented the initial fall of SAP and attenuated the SAP recovery along with augmentation of the late increase in Rspl. The 2-h survival rate was significantly smaller in either pretreatment group than in the control group (100%). Plasma levels of ANG II and vasopressin increased to 3.8- and 9.8-fold, respectively, at 30 min after antigen in the control group, whereas captopril pretreatment inhibited the increase in ANG II. In conclusion, inhibition of ANG II or vasopressin exacerbates anaphylaxis-induced hypotension in anesthetized rats.

Vascular perfusion limits mesenteric lymph flow during anaphylactic hypotension in rats

To determine fluid extravasation in the splanchnic vascular bed during anaphylactic hypotension, the mesenteric lymph flow (Q(lym)) was measured in anesthetized rats sensitized with ovalbumin, along with the systemic arterial pressure (P(sa)) and portal venous pressure (P(pv)). When the antigen was injected into the sensitized rats (n = 10), P(sa) decreased from 125 ± 4 to 37 ± 2 mmHg at 10 min with a gradual recovery, whereas P(pv) increased by 16 mmHg at 2 min and returned to the baseline at 10 min. Q(lym) increased 3.3-fold from the baseline of 0.023 ± 0.002 g/min to the peak levels of 0.075 ± 0.009 g/min at 2 min and returned to the baseline within 12 min. The lymph protein concentrations increased after antigen, a finding indicating increased vascular permeability. To determine the role of the P(pv) increase in the antigen-induced increase in Q(lym), P(pv) of the nonsensitized rats (n = 10) was mechanically elevated in a manner similar to that of the sensitized rats by compressing the portal vein near the hepatic hilus. Unexpectedly, P(pv) elevation alone produced a similar increase in Q(lym), with the peak comparable to that of the sensitized rats. This finding aroused a question why the antigen-induced increase in Q(lym) was limited despite the presence of increased vascular permeability. Thus the changes in splanchnic vascular surface area were assessed by measuring the mesenteric arterial flow. The mesenteric arterial flow was decreased much more in the sensitized rats (75%; n = 5) than the nonsensitized P(pv) elevated rats (50%; n = 5). In conclusion, mesenteric lymph flow increases transiently after antigen presumably due to increased capillary pressure of the splanchnic vascular bed via downstream P(pv) elevation and perfusion and increased vascular permeability in anesthetized rats. However, this increased extravasation is subsequently limited by decreases in vascular surface area and filtration pressure.

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.

Nitric oxide and β 2 -adrenoceptor activation attenuate pulmonary vasoconstriction during anaphylactic hypotension in anesthetized BALB/c mice

ABSTRACT Systemic anaphylaxis accompanies pulmonary vasoconstriction and bronchoconstriction, which may contribute to increased right heart afterload, and finally anaphylactic hypotension. However, the pulmonary response to anaphylaxis is not known in mice. We determined the pulmonary vascular and bronchial response to systemic anaphylaxis in anesthetized BALB/c mice. We also clarified the roles of β-adrenoceptors, nitric oxide, and cyclooxygenase metabolites in these responses. Anaphylaxis was induced by an intravenous injection of the ovalbumin antigen into open-chest artificially ventilated sensitized mice. Mean arterial pressure, systolic pulmonary arterial pressure, central venous pressure, airway pressure, and aortic blood flow were continuously measured. In sensitized control mice, mean arterial pressure, and aortic blood flow substantially decreased soon after the antigen injection, while systolic pulmonary arterial pressure and airway pressure did not increase. In contrast, in mice pretreated with either the β2-adrenoceptor antagonist ICI 118,551 (0.2 mg/kg; n = 6), or L-NAME (50 mg/kg; n = 6), but not with the β1-adrenoceptor antagonist atenolol (2 mg/kg; n = 6) or indomethacin (5 mg/kg; n = 6), systolic pulmonary arterial pressure increased by 7 mmHg at 1.5 min after antigen. In L-NAME pretreated mice, pulmonary hypertension was sustained over 30 min of the experimental period. Airway pressure did not significantly change after antigen in any mice studied. In conclusion, pulmonary response to systemic anaphylaxis does not increase the right heart afterload and, therefore, may not contribute to the initial decrease in venous return and anaphylactic hypotension in anesthetized mice. β2-adrenoceptor activation and nitric oxide, but not β1-adrenoceptor activation or cyclooxygenase metabolites, attenuate the antigen-induced pulmonary vasoconstriction.

Systemic vasoconstriction modulates the responses of pulmonary vasculature and airway to vasoconstrictors in anesthetized rats

ABSTRACT Purpose: The physiological responses of the pulmonary vasculature and airway to various vasoconstrictors were studied using isolated perfused lungs and pulmonary arteries, but these responses were not systematically studied in in vivo rats. We determined these responses and modulating effects of systemic circulation in anesthetized rats. Methods: We measured directly pulmonary arterial pressure (PAP), left atrial pressure (LAP), aortic blood flow, and airway pressure (AWP) to determine pulmonary vascular resistance (PVR), following injections of angiotensin II (ANG II), endothelin-1 (ET-1), vasopressin, phenylephrine and thromboxane A2 mimetic U46619 in anesthetized SD rats. Results: ANG II, phenylephrine and vasopressin at high doses caused strong systemic vasoconstriction and left heart overload, resulting in a transient increase in LAP and pulmonary congestion, which consequently decreased PVR. Nonetheless, prior to LAP elevation, PVR was slightly but significantly increased by ANG II and phenylephrine. In contrast, ET-1 and U46619 substantially increased PVR in the absence of LAP elevation, while vasopressin did not increase PVR. In separate experiments, PAP and AWP increased when LAP was forcedly elevated. AWP was increased by U46619 through bronchoconstriction and by the other agents through increased LAP-induced pulmonary congestion. Conclusion: Airway constriction is induced by U46619, and pulmonary vasoconstriction is induced strongly by U46619 and ET-1, and weakly by ANG II and phenylephrine, but not by vasopressin in anesthetized rats. ANG II, vasopressin and phenylephrine exert indirectly a transient pulmonary vasodilatory action due to pulmonary congestion evoked by strong systemic vasoconstriction, which may account for weak pulmonary pressor responses to these agents.

Dynamical mechanisms of phase-2 early afterdepolarizations in human ventricular myocytes: insights from bifurcation analyses of two mathematical models

Early afterdepolarization (EAD) is known as a cause of ventricular arrhythmias in long QT syndromes. We theoretically investigated how the rapid (IKr) and slow (IKs) components of delayed-rectifier K+ channel currents, L-type Ca2+ channel current (ICaL), Na+/Ca2+ exchanger current (INCX), Na+-K+ pump current (INaK), intracellular Ca2+ (Cai) handling via sarcoplasmic reticulum (SR), and intracellular Na+ concentration (Nai) contribute to initiation, termination, and modulation of phase-2 EADs, using two human ventricular myocyte models. Bifurcation structures of dynamical behaviors in model cells were explored by calculating equilibrium points, limit cycles (LCs), and bifurcation points as functions of parameters. EADs were reproduced by numerical simulations. The results are summarized as follows: 1) decreasing IKs and/or IKr or increasing ICaL led to EAD generation, to which mid-myocardial cell models were especially susceptible; the parameter regions of EADs overlapped the regions of stable LCs. 2) Two types of EADs (termination mechanisms), IKs activation-dependent and ICaL inactivation-dependent EADs, were detected; IKs was not necessarily required for EAD formation. 3) Inhibiting INCX suppressed EADs via facilitating Ca2+-dependent ICaL inactivation. 4) Cai dynamics (SR Ca2+ handling) and Nai strongly affected bifurcations and EAD generation in model cells via modulating ICaL, INCX, and INaK Parameter regions of EADs, often overlapping those of stable LCs, shifted depending on Cai and Nai in stationary and dynamic states. 5) Bradycardia-related induction of EADs was mainly due to decreases in Nai at lower pacing rates. This study demonstrates that bifurcation analysis allows us to understand the dynamical mechanisms of EAD formation more profoundly. NEW & NOTEWORTHY We investigated mechanisms of phase-2 early afterdepolarization (EAD) by bifurcation analyses of human ventricular myocyte (HVM) models. EAD formation in paced HVMs basically depended on bifurcation phenomena in non-paced HVMs, but was strongly affected by intracellular ion concentrations in stationary and dynamic states. EAD generation did not necessarily require IKs.