Mechanisms for hypothermia during anaphylactic hypotension in awake rats.

Hypothermia develops during systemic anaphylaxis in rodents. The aim of this study was to elucidate the mechanism for the hypothermia by assessing the roles of locomotor activity, tail heat dissipation, heat production in the brown adipose tissue (BAT) activity, and chemical mediators during ovalbumin-induced anaphylactic hypotension in awake rats. We measured the core body temperature (Tcore) and mean blood pressure (MBP), along with the surface temperature of the interscapular region (TiScap), an indirect measure of BAT activity, and the tail (Ttail). During anaphylaxis, MBP decreased to the nadir of 53 ± 2 mmHg at 8 min with recovery toward baseline. Tcore began to decrease at 7.5 min with the nadir of 36.1 ± 0.2°C at 30 min from the baseline of 38.0 ± 0.1°C. TiScap also significantly decreased, but its onset was preceded by that of Tcore. Ttail decreased after antigen, suggesting the absence of increased heat dissipation from the tail. The physical activity, as evaluated by moved distances, did not decrease until 20 min after antigen, followed by a progressive decrease. Reduced movement using a restraint maneuver not only reduced Tcore in nonsensitized rats but also augmented the anaphylactic hypothermia in the early phase (1.5-18 min) in sensitized rats. Combined antagonism against platelet-activating factor (PAF) and histamine H1 receptors abolished antigen-induced hypotension but only attenuated hypothermia. In conclusion, decreased locomotor activity, but not tail heat dissipation or decreased BAT activity, may at least in part contribute to this hypothermia. PAF and histamine are involved mainly in hypotension but only partly in hypothermia during rat anaphylaxis.NEW & NOTEWORTHY Anaphylactic shock is a life-threatening systemic hypotension. Hypothermia is observed during systemic anaphylaxis of rats. We determined the mechanism as follows: decreased locomotor activity, but not tail heat dissipation or decreased BAT activity, may at least in part contribute to this hypothermia. PAF and histamine are involved mainly in hypotension, but only partly in hypothermia during rat anaphylaxis.

Theoretical prediction of early afterdepolarization-evoked triggered activity formation initiating ventricular reentrant arrhythmias.

BACKGROUND AND OBJECTIVE: Excessive prolongation of QT interval on ECGs in patients with congenital/acquired long QT syndrome and heart failure is a sign suggesting the development of early afterdepolarization (EAD), an abnormal repolarization in the action potential of ventricular cardiomyocytes. The development of EAD has been believed to be a trigger for fatal tachyarrhythmia, which can be a risk for sudden cardiac death. The role of EAD in triggering ventricular tachycardia (VT) remains unclear. The aim of this study was to elucidate the mechanism of EAD-induced triggered activity formation that leads to the VT such as Torsades de Pointes. METHODS: We investigated the relationship between EAD and tachyarrhythmia initiation by constructing homogeneous myocardial sheet models consisting of the mid-myocardial cell version of a human ventricular myocyte model and performing simulations of excitation propagation. RESULTS: A solitary island-like (clustering) occurrence of EADs in the homogeneous myocardial sheet could induce a focal excitation wave. However, reentrant excitation, an entity of tachyarrhythmia, was not able to be triggered regardless of the EAD cluster size when the focal excitation wave formed a repolarization potential difference boundary consisting of only a convex surface. The discontinuous distribution of multiple EAD clusters in the ventricular tissue formed a specific repolarization heterogeneity due to the repolarization potential difference, the shape of which depended on EAD cluster size and placed intervals. We found that the triggered activity was formed in such a manner that the repolarization potential difference boundary included a concave surface. CONCLUSIONS: The formation of triggered activity that led to tachyarrhythmia required not only the occurrence of EAD onset-mediated focal excitation wave but also a repolarization heterogeneity-based specific repolarization potential difference boundary shape formed within the tissue.

Hepatic glycogenolysis and hypometabolism induced by chemogenetic stimulation of C1 neurons.

The precise regulation of blood glucose levels is indispensable for maintaining physiological functions. C1 neurons determine the outflow of the autonomic nervous and endocrine systems to maintain blood glucose levels in the body. In contrast, activation of C1 neurons induces a decrease in activity, suggesting that hypoactivity also participates in maintaining blood glucose levels. To examine this, we evaluated both glycogenolysis and hypometabolism induced by the selective activation of C1 neurons. We used DbhCre/0 mice expressing receptors for chemogenetic tools in C1 neurons, resulting from microinjection of the viral vector. C1 neurons were activated by intraperitoneal injection of clozapine N-oxide (CNO). The chemogenetic activation of C1 neurons significantly decreased body temperature, oxygen consumption and carbon dioxide production. On the other hand, blood glucose levels were increased by activation of C1 neurons 2 h after CNO administration, even in the fasting state. In this situation, an increase in glucagon and corticosterone levels was observed, while hepatic glycogen content decreased significantly. Plasma insulin levels were not changed by the activation of C1 neurons despite the increase in blood glucose level. Furthermore, adrenal sympathetic nerve activity was significantly increased by the activation of C1 neurons, and plasma catecholamine levels increased significantly. In conclusion, the selective activation of C1 neurons using chemogenetic tools induced an increase in blood glucose levels, probably as a result of hepatic glycogenolysis and hypometabolism. KEY POINTS: Chemogenetic activation of C1 neurons in medulla oblongata decreased body temperature. Oxygen consumption and carbon dioxide production were decreased by chemogenetic activation of C1 neurons in medulla oblongata. Blood glucose levels were increased by chemogenetic activation of C1 neurons in medulla oblongata. Chemogenetic activation of C1 neurons in medulla oblongata increased glucagon, corticosterone and catecholamine levels in plasma. An increase in blood glucose levels by activation of C1 neurons occurred due to the combined effect of hepatic glycogenolysis and hypometabolism.

Repeated activation of C1 neurons in medulla oblongata decreases anti-inflammatory effect via the hypofunction of the adrenal gland adrenergic response.

The immune system is known to be controlled by the autonomic nervous system including sympathetic and parasympathetic (vagus) nerves. C1 neurons in the medulla oblongata, which participate in the control of the autonomic nervous system, are responders to stressors and regulate the immune system. Short-term activation of C1 neurons suppresses inflammation, while the effect of a long-term activation of these neurons on the inflammatory reflex is unclear. We, herein, demonstrate that the coactivation of both the splenic sympathetic nerves and the adrenal gland adrenergic response are indispensable for the prognosis of acute lung injury. The chemogenetic activation of C1 neurons increased plasma catecholamine including adrenaline and noradrenaline levels. The deletion of catecholaminergic cells using local injections of viral vector in the adrenal gland abolished the protective effect against acute lung injury when the C1 neurons were stimulated by either chemogenetic or optogenetic tools. Furthermore, repeated activation of C1 neurons using chemogenetic tool inhibited the adrenal response without affecting the plasma noradrenaline levels, eliminated the protective effect against acute lung injury. This was rescued by the isoprenaline administration. We concluded that the maintenance of an adrenergic response via C1 neurons in the adrenal gland is a prerequisite for the delivery of an effective anti-inflammatory response.

Poly(I:C) promotes neurotoxic amyloid ß accumulation through reduced degradation by decreasing neprilysin protein levels in astrocytes.

Inflammation associated with viral infection of the nervous system has been involved in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD) and multiple sclerosis. Polyinosinic:polycytidylic acid (poly[I:C]) is a Toll-like receptor 3 (TLR3) agonist that mimics the inflammatory response to systemic viral infections. Despite growing recognition of the role of glial cells in AD pathology, their involvement in the accumulation and clearance of amyloid ß (Aß) in the brain of patients with AD is poorly understood. Neprilysin (NEP) and insulin-degrading enzyme (IDE) are the main Aß-degrading enzymes in the brain. This study investigated whether poly(I:C) regulated Aß degradation and neurotoxicity by modulating NEP and IDE protein levels through TLR3 in astrocytes. To this aim, primary rat primary astrocyte cultures were treated with poly(I:C) and inhibitors of the TLR3 signaling. Protein levels were assessed by Western blot. Aß toxicity to primary neurons was measured by lactate dehydrogenase release. Poly(I:C) induced a significant decrease in NEP levels on the membrane of astrocytes as well as in the culture medium. The degradation of exogenous Aß was markedly delayed in poly(I:C)-treated astrocytes. This delay significantly increased the neurotoxicity of exogenous Aß1-42. Altogether, these results suggest that viral infections induce Aß neurotoxicity by decreasing NEP levels in astrocytes and consequently preventing Aß degradation.

[Electrophysiological Mechanism Underlying Vagal Nerve Activity in Mice].

The autonomic nervous system, which consists of sympathetic and parasympathetic nerves, plays an important role in the regulation of various functions of body organs. Recent studies have reported that vagal afferents that transmit information from the periphery to the brain function as an important signal pathway for dissemination of details regarding nutritional status, as well as the cardiovascular system and inflammation. In this review, we describe the measurement analysis of vagal nerve activity in mice using an in vivo electrophysiological method and account for the role and mechanism of action of vagal nerves in homeostasis.

Protein kinases A and C regulate amyloid-ß degradation by modulating protein levels of neprilysin and insulin-degrading enzyme in astrocytes.

The pathology of sporadic Alzheimer's disease is hallmarked by altered signal transduction via the neurotransmitter receptor-G-protein-mediated protein kinase A (PKA) and protein kinase C (PKC) pathways. Because the accumulation of amyloid-ß (Aß) depends on its rates of synthesis and clearance, the metabolic pathway of Aß in the brain and the entire body warrants exploration. The two major enzymes involved in Aß degradation in the brain are believed to be the neprilysin and insulin-degrading enzyme (IDE). This study investigated whether PKA and PKC regulate the degradation of Aß by modulating the protein levels of neprilysin and IDE in astrocytes. Activation of PKA induced a significant decrease in neprilysin protein levels in cultured astrocytes, whereas activation of PKC induced a significant decrease in the protein level of neprilysin and an increase in the protein level of IDE. Following activation of PKC, the reduction of neprilysin was achieved by its secretion into the culture media. Moreover, PKA-activated astrocytes significantly delayed the degradation of exogenous Aß, whereas PKC-activated astrocytes significantly facilitated its degradation. These results suggest that PKA and PKC regulate Aß degradation in astrocytes through a decrease in the protein level of neprilysin and an increase in neprilysin secretion and protein levels of IDE, respectively.

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-1ß, 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.

The liver-brain-gut neural arc maintains the Treg cell niche in the gut.

Recent clinical and experimental evidence has evoked the concept of the gut-brain axis to explain mutual interactions between the central nervous system and gut microbiota that are closely associated with the bidirectional effects of inflammatory bowel disease and central nervous system disorders1-4. Despite recent advances in our understanding of neuroimmune interactions, it remains unclear how the gut and brain communicate to maintain gut immune homeostasis, including in the induction and maintenance of peripheral regulatory T cells (pTreg cells), and what environmental cues prompt the host to protect itself from development of inflammatory bowel diseases. Here we report a liver-brain-gut neural arc that ensures the proper differentiation and maintenance of pTreg cells in the gut. The hepatic vagal sensory afferent nerves are responsible for indirectly sensing the gut microenvironment and relaying the sensory inputs to the nucleus tractus solitarius of the brainstem, and ultimately to the vagal parasympathetic nerves and enteric neurons. Surgical and chemical perturbation of the vagal sensory afferents at the hepatic afferent level reduced the abundance of colonic pTreg cells; this was attributed to decreased aldehyde dehydrogenase (ALDH) expression and retinoic acid synthesis by intestinal antigen-presenting cells. Activation of muscarinic acetylcholine receptors directly induced ALDH gene expression in both human and mouse colonic antigen-presenting cells, whereas genetic ablation of these receptors abolished the stimulation of antigen-presenting cells in vitro. Disruption of left vagal sensory afferents from the liver to the brainstem in mouse models of colitis reduced the colonic pTreg cell pool, resulting in increased susceptibility to colitis. These results demonstrate that the novel vago-vagal liver-brain-gut reflex arc controls the number of pTreg cells and maintains gut homeostasis. Intervention in this autonomic feedback feedforward system could help in the development of therapeutic strategies to treat or prevent immunological disorders of the gut.

Central Injection of Leptin Increases Sympathetic Nerve Outflows to the Stomach and Spleen in Anesthetized Rats.

BACKGROUND/AIM: Leptin, one of the hormones produced in white adipose tissue, is an efferent sympathetic stimulator. Actually, an injection of leptin into the brain has been shown to activate sympathetic nerve activities innervating the kidney, adrenal gland, adipose tissues, liver, and lumbar in rats. MATERIALS AND METHODS: This study investigated the effects of an intracerebroventricular injection of leptin on the activities of sympathetic nerves innervating the stomach and spleen in anesthetized rats. RESULTS: Leptin injection activated the neural activities of sympathetic traffic to both the stomach and spleen. In addition, to investigate the role of AMP-activated protein kinase (AMPK), the effects of 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR), an AMPK activator, or compound C, an AMPK inhibitor, on leptin-induced sympathoexcitation, were assessed. Central pretreatment with AICAR or compound C eliminated not only leptin-induced gastric sympathoexcitation but also leptin-induced splenic sympathoexcitation. CONCLUSION: Leptin stimulates efferent sympathetic outflow to the stomach and spleen through the hypothalamic AMPK.

Tonic contraction develops in the colon during anaphylactic hypotension in anesthetized rats.

Diarrhea is a gastrointestinal symptom associated with systemic anaphylaxis and could be induced by increased colonic motility. We determined colonic motility and expulsion by measuring the intracolonic pressure (ICP) and expelled fluid weight in anesthetized rats during anaphylactic hypotension. Substantial systemic hypotension occurred in every sensitized rat after antigen injection. One min after antigen injection, ICP began to increase and remained elevated for 5 min, which was revealed to represent tonic contraction by the video-recording procedure, and was accompanied by increased colonic fluid expulsion. Parasympathectomy composed of subdiaphragmatic vagotomy combined with pelvic nerve transection reduced the duration of the tonic contraction, but not expelled colonic fluid. Furthermore, denervation of afferent parasympathetic nerves produced essentially the same effect as parasympathectomy. Sympathectomy did not significantly change any parameters. In conclusion, the colonic motility during anaphylactic hypotension is characterized by 5-min lasting tonic contraction which is associated with increased colonic fluid expulsion and is involved by parasympathetic nerves, especially their afferents, but not sympathetic nerves, in anesthetized rats.

Anaphylaxis stimulates afferent vagal nerve activity and efferent sympathetic nerve activity in the stomach of anesthetized rats.

Systemic anaphylaxis is a life-threatening and allergic reaction that affects various organs. We previously reported that, in the stomach, gastric vasoconstriction occurring at the late phase (15-55 min after injection of ovalbumin antigen) was observed in anesthetized rats sensitized with ovalbumin. In addition, anaphylaxis enhances gastric motility and delays emptying. However, the role of extrinsic autonomic nervous system on antigen-induced gastric alterations was not known. Thus, using the same rat anaphylaxis model, we aimed to determine the changes in the efferent and afferent autonomic nerve activities in the stomach during anaphylactic hypotension. The findings showed that injection of ovalbumin antigen caused substantial systemic hypotension in all sensitized rats. The efferent gastric sympathetic nerve activity (ef-GSNA), but not the efferent vagal nerve activity, increased only at the early phase (1-10 min after injection of ovalbumin antigen) and showed baroreceptor reflex, as evidenced by a stimulatory response to sodium nitroprusside-induced hypotension. In general, excitation of ef-GSNA could induce pylorus sphincter contraction and gastric vasoconstriction. In the present study, we found that sympathectomy attenuated the anaphylaxis-induced decrease in gastric flux but not the increase in gastric vascular resistance. Thus, the increase in ef-GSNA may cause anaphylactic pylorus sphincter contraction but not anaphylactic gastric vasoconstriction. On the other hand, the afferent gastric vagal nerve activity, but not the afferent sympathetic nerve activity, increased during the early phase of anaphylactic hypotension. However, vagotomy produced no effects on the anaphylactic gastric dysfunction. In conclusion, the gastric sympathetic nerves partly modulate stomach function during systemic anaphylaxis.

Multiple Dynamical Mechanisms of Phase-2 Early Afterdepolarizations in a Human Ventricular Myocyte Model: Involvement of Spontaneous SR Ca 2+ Release.

Early afterdepolarization (EAD) is known to cause lethal ventricular arrhythmias in long QT syndrome (LQTS). In this study, dynamical mechanisms of EAD formation in human ventricular myocytes (HVMs) were investigated using the mathematical model developed by ten Tusscher and Panfilov (Am J Physiol Heart Circ Physiol 291, 2006). We explored how the rapid (IKr) and slow (IKs) components of delayed-rectifier K+ channel currents, L-type Ca2+ channel current (ICa L), Na+/Ca2+ exchanger current (INCX), and intracellular Ca2+ handling via the sarcoplasmic reticulum (SR) contribute to initiation, termination and modulation of phase-2 EADs during pacing in relation to bifurcation phenomena in non-paced model cells. Parameter-dependent dynamical behaviors of the non-paced model cell were determined by calculating stabilities of equilibrium points (EPs) and limit cycles, and bifurcation points to construct bifurcation diagrams. Action potentials (APs) and EADs during pacing were reproduced by numerical simulations for constructing phase diagrams of the paced model cell dynamics. Results are summarized as follows: (1) A modified version of the ten Tusscher-Panfilov model with accelerated ICaL inactivation could reproduce bradycardia-related EADs in LQTS type 2 and ß-adrenergic stimulation-induced EADs in LQTS type 1. (2) Two types of EADs with different initiation mechanisms, ICaL reactivation-dependent and spontaneous SR Ca2+ release-mediated EADs, were detected. (3) Termination of EADs (AP repolarization) during pacing depended on the slow activation of IKs. (4) Spontaneous SR Ca2+ releases occurred at higher Ca2+ uptake rates, attributable to the instability of steady-state intracellular Ca2+ concentrations. Dynamical mechanisms of EAD formation and termination in the paced model cell are closely related to stability changes (bifurcations) in dynamical behaviors of the non-paced model cell, but they are model-dependent. Nevertheless, the modified ten Tusscher-Panfilov model would be useful for systematically investigating possible dynamical mechanisms of EAD-related arrhythmias in LQTS.

Insulin-signaling Pathway Regulates the Degradation of Amyloid ß-protein via Astrocytes.

Alzheimer's disease (AD) has been considered as a metabolic dysfunction disease associated with impaired insulin signaling. Determining the mechanisms underlying insulin signaling dysfunction and resistance in AD will be important for its treatment. Impaired clearance of amyloid-ß peptide (Aß) significantly contributes to amyloid accumulation, which is typically observed in the brain of AD patients. Reduced expression of important Aß-degrading enzymes in the brain, such as neprilysin (NEP) and insulin-degrading enzyme (IDE), can promote Aß deposition in sporadic late-onset AD patients. Here, we investigated whether insulin regulates the degradation of Aß by inducing expression of NEP and IDE in cultured astrocytes. Treatment of astrocytes with insulin significantly reduced cellular NEP levels, but increased IDE expression. The effects of insulin on the expression of NEP and IDE involved activation of an extracellular signal-regulated kinase (ERK)-mediated pathway. The reduction in cellular NEP levels was associated with NEP secretion into the culture medium, whereas IDE was increased in the cell membranes. Moreover, insulin-treated astrocytes significantly facilitated the degradation of exogenous Aß within the culture medium. Interestingly, pretreatment of astrocytes with an ERK inhibitor prior to insulin exposure markedly inhibited insulin-induced degradation of Aß. These results suggest that insulin exposure enhanced Aß degradation via an increase in NEP secretion and IDE expression in astrocytes, via activation of the ERK-mediated pathway. The inhibition of insulin signaling pathways delayed Aß degradation by attenuating alterations in NEP and IDE levels and competition with insulin and Aß. Our results provide further insight into the pathological relevance of insulin resistance in AD development.

Anaphylactic hypotension causes renal and adrenal sympathoexcitaion and induces c-fos in the hypothalamus and medulla oblongata.

NEW FINDINGS: What is the central question of this study? Whether anaphylaxis affects sympathetic outflows to the brown adipose tissue (BAT) and adrenal gland and whether anaphylaxis affects some brain areas in association with sympathetic regulation. What is the main finding and its importance? Sympathoexcitatory responses to anaphylaxis occurred regionally in the kidney and adrenal gland, but not in the thermogenesis-related BAT. Further, anaphylactic hypotension also caused increase in c-fos immunoreactivity in the hypothalamic and medullary areas. Moreover, catecholaminergic neurons of the brainstem cause adrenal sympathoexcitation in a baroreceptor-independent manner. ABSTRACT: We previously reported that sympathetic nerve activity (SNA) to the kidney and the hindlimb increases during anaphylactic hypotension in anaesthetized rats. Based on this evidence, we examined effects of anaphylactic hypotension on SNA to the brown adipose tissue (BAT), and the adrenal gland and kidney in anaesthetized rats. We demonstrated that adrenal and renal SNA, but not BAT-SNA, were stimulated. In addition, the effects of anaphylaxis on neural activities of the hypothalamic and medullary nuclei, which are candidates for relaying efferent SNA to the peripheral organs, were investigated via immunohistochemical staining of c-fos. Anaphylaxis increased c-fos expression in the neurons of the paraventricular nucleus (PVN) of the hypothalamus and in those of the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM) of the medulla oblongata; c-fos was expressed in γ-aminobutyric acid (GABA)-ergic neurons of the NTS and in the catecholaminergic neurons of the RVLM. In addition, c-fos expression in the rostral NTS and mid NTS during anaphylaxis was reduced by sinoaortic baroreceptor denervation; however, increased c-fos expression in the caudal NTS and RVLM or adrenal sympathoexcitation were not affected by sinoaortic baroreceptor denervation. These results indicated that anaphylactic hypotension activates the hypothalamic PVN and the medullary NTS and RVLM independently of the baroreflex pathway. Further, it stimulated efferent SNA to the adrenal gland and kidney to restore blood pressure.

ß2-Adrenoceptor Blockade Deteriorates Systemic Anaphylaxis by Enhancing Hyperpermeability in Anesthetized Mice.

PURPOSE: Patients treated with propranolol, a nonselective ß-adrenoceptor antagonist, develop severe anaphylaxis, but the mechanism remains unknown. We determined effects of ß1- and ß2-adrenoceptor antagonists on the anaphylaxis-induced increase in vascular permeability in mice. METHODS: In anesthetized ovalbumin-sensitized C57BL mice, mean arterial blood pressure (MBP) was measured, and Evans blue dye extravasation and hematocrit (Hct) were assessed at 20 minutes after antigen injection. The following pretreatment groups (n=7/group) were studied: (1) sensitized control (non-pretreatment), (2) propranolol, (3) the selective ß2-adrenoceptor antagonist ICI 118,551, (4) the selective ß1-adrenoceptor antagonist atenolol, (5) adrenalectomy, (6) the selective ß2-adrenoceptor agonist terbutaline, and (7) non-sensitized groups. RESULTS: The antigen injection decreased MBP, and increased Hct and vascular permeability in the kidney, lung, mesentery, and intestine, but not in the liver or spleen. Pretreatment with ICI 118,551, propranolol and adrenalectomy, but not atenolol, reduced the survival rate and augmented the increases in Hct and vascular permeability in the kidney, intestine, and lung as compared with the sensitized control group. Pretreatment with terbutaline abolished the antigen-induced alterations. Plasma epinephrine levels were increased significantly in the sensitize control mice. CONCLUSIONS: Blockade of ß2-adrenoceptor can deteriorate systemic anaphylaxis by augmenting hyperpermeability-induced increase in plasma extravasation by inhibiting beneficial effects of epinephrine released from the adrenal glands in anesthetized mice.

Renal response to anaphylaxis in anesthetized rats and isolated perfused rat kidneys: roles of nitric oxide.

We determined the renal responses to anaphylaxis and the effects of a nitric oxide synthesis inhibitor, L-NAME, in anesthetized rats and isolated perfused rat kidneys. After the ovalbumin antigen injection, the sensitized rats showed transient and substantial decreases in mean blood pressure and renal blood flow and an increase in renal vascular resistance. Creatinine clearance, a measure of renal function, decreased to 53% baseline at 2 h after antigen. L-NAME pretreatment significantly enhanced the antigen-induced renal vasoconstriction and renal dysfunction. Moreover, plasma creatinine levels significantly increased only in the L-NAME pretreated rats. Separately, in isolated perfused kidneys, we observed the antigen-induced renal vasoconstriction and its augmentation by L-NAME. In conclusion, the renal vascular response to the antigen is vasoconstriction, which is enhanced by L-NAME in both isolated perfused rat kidneys and anesthetized rats; it is accompanied by renal dysfunction, which is also augmented by L-NAME.

Gastric vascular and motor responses to anaphylactic hypotension in anesthetized rats, in comparison to those with hemorrhagic or vasodilator-induced hypotension.

Anaphylactic shock is life-threatening, but pathophysiology of the stomach lesion remains unclear. We determined gastric hemodynamics and gastric functions during anaphylactic hypotension, as compared to hypotension induced by hemorrhage or sodium nitroprusside (SNP) in anesthetized and ovalbumin-sensitized Sprague-Dawley rats. Systemic arterial pressure, portal venous pressure, and gastric arterial blood flow were measured, and gastric vascular resistance (GVR) was determined. Separately, the intragastric pressure (IGP) and gastric effluent, as a measure of gastric flux, were continuously measured. During anaphylaxis, GVR decreased only transiently at 0.5 min, followed by an increase. IGP increased markedly, while gastric flux decreased. During hemorrhage, GVR and IGP increased, while gastric flux did not change. When SNP was injected, both GVR and IGP decreased and gastric flux increased only just after injection. In conclusion, gastric vasodilatation occurs only transiently after antigen injection, and gastric motility increases, but gastric emptying deceases during anaphylactic hypotension in anesthetized rats.

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.

Epigallocatechin gallate induces extracellular degradation of amyloid ß-protein by increasing neprilysin secretion from astrocytes through activation of ERK and PI3K pathways.

Amyloid-ß (Aß) production and clearance in the brain is a crucial focus of investigations into the pathogenesis of Alzheimer disease. Imbalance between production and clearance leads to accumulation of Aß. The important Aß-degrading enzymes in the brain are neprilysin (NEP) and insulin-degrading enzyme (IDE), and defective enzyme expression may facilitate Aß deposition in sporadic late-onset AD patients. It has been suggested that epigallocatechin gallate (EGCG), a member of the catechin family, might be an effective treatment for AD, because it has been shown to elevate NEP expression. Therefore, we examined whether catechins, which are functional components of common foods, could regulate the degradation of Aß by inducing NEP and IDE expression. We also investigated the role of catechins in activating intracellular signal transduction in astrocytes. Treatment of cultured rat astrocytes with EGCG significantly reduced the expression of NEP, but not IDE, in a concentration- and time-dependent manner. NEP expression in cultured astrocytes was suppressed by activation of extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K), and reduced NEP expression was accompanied by an increase of NEP release into the extracellular space (culture medium). Moreover, culture medium from EGCG-treated astrocytes facilitated the degradation of exogenous Aß. These results suggest that EGCG may have a beneficial effect on AD by activating ERK-and PI3K-mediated pathways in astrocytes, thus increasing astrocyte secretion of NEP and facilitating degradation of Aß.