Neuropeptide Y1- and Y2-receptor-mediated cardiovascular effects in the anesthetized guinea pig, rat, and rabbit

Life-Threatening Arrhythmias in Patients With Takotsubo Syndrome: Insights Into Pathophysiology and Treatment Innovations

Takotsubo syndrome (TTS) is a reversible form of acute myocardial injury due to a neurocardiogenic mechanism associated with a relevant risk for life-threatening ventricular arrhythmias, occurring in up to 25% of all patients and including both ventricular arrhythmias (especially) in the context of QT prolongation and atrial tachy- or bradyarrhythmias. The pathogenetic mechanisms of TTS-related arrhythmic complications are not completely understood, and there are no randomized clinical trials addressing the pharmacologic and nonpharmacologic management in this specific setting. In this narrative review, the authors provide an overview of the pathogenesis and the therapeutic management of arrhythmic complications in patients with TTS, along with the future perspectives and the remaining knowledge gaps in this field.

Gill transcriptomes reveal expression changes of genes related with immune and ion transport under salinity stress in silvery pomfret (Pampus argenteus)

Salinity is a major ecological factor in the marine environment, and extremely important for the survival, development, and growth of fish. In this study, gill transcriptomes were examined by high-throughput sequencing at three different salinities (12 ppt as low salinity, 22 ppt as control salinity, and 32 ppt as high salinity) in an importantly economical fish silvery pomfret. A total of 187 genes were differentially expressed, including 111 up-regulated and 76 down-regulated transcripts in low-salinity treatment group and 107 genes differentially expressed, including 74 up-regulated and 33 down-regulated transcripts in high-salinity treatment group compared with the control group, respectively. Some pathways including NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, Toll-like receptor pathway, cardiac muscle contraction, and vascular smooth muscle contraction were significantly enriched. qPCR analysis further confirmed that mRNA expression levels of immune (HSP90A, IL-1β, TNFα, TLR2, IP-10, MIG, CCL19, and IL-11) and ion transport-related genes (WNK2, NPY2R, CFTR, and SLC4A2) significantly changed under salinity stress. Low salinity stress caused more intensive expression changes of immune-related genes than high salinity. These results imply that salinity stress may affect immune function in addition to regulating osmotic pressure in silvery pomfret.

Pharmacological characterization, cellular localization and expression profile of NPY receptor subtypes Y2 and Y7 in large yellow croaker, Larimichthys crocea

Neuropeptide Y (NPY) receptors are suggested to mediate the multi-physiological functions of NPY family peptides, such as food intake, in teleost fish. However, the structure and signaling of fish NPY receptors are yet to be fully elucidated. In this study, we report the cloning and characterization of two neuropeptide Y receptor subtypes, Y2 (NPY2R) and Y7 (NPY7R), in yellow croaker Larimichthys crocea (L. crocea) (LcNPY2R, LcNPY7R). The gene structure, pharmacological characterization, cell location, and tissue expression of these two receptors were explored. The phylogenetic results showed that LcNPY2R and LcNPY7R had typical G protein-coupled receptor profiles, associated with the Y2 subfamily, with coding sequences that are highly conserved in vertebrates. The expression of both LcNPY2R and LcNPY7R could be activated by LcNPY in HEK293 cells. However, truncated LcNPY_18-36 was only able to activate LcNPY2R at the same level as full length LcNPY. Expression analysis revealed that LcNPY2R mRNA was predominantly expressed in the intestine and liver, whereas LcNPY7R was expressed in the stomach, which indicated that both receptors were related to the digestive system. Overall, our data establishes a molecular basis to determine the actions of LcNPY2R and LcNPY7R, which could be used to elucidate the conserved roles of these receptor-ligand pairs in vertebrates.

Cloning, expression, and ligand-binding characterization of two neuropeptide Y receptor subtypes in orange-spotted grouper, Epinephelus coioides

As one of the most important multifunctional peptides, neuropeptide Y (NPY) performs its physiological functions through different subtype receptors. In this study, full-length cDNAs of two NPY receptors (YRs) in orange-spotted grouper (Epinephelus coioides) were cloned and named npy8br (y8b) and npy2r (y2). Phylogenetic analysis indicated that the Y8b receptor is an ortholog of the teleostean Y8b receptor, which belongs to the Y1 subfamily, and the Y2 receptor is an ortholog of the teleostean Y2 receptor, which belongs to the Y2 subfamily. Both of the YRs have G protein-coupled receptor family profiles. Multiple alignments demonstrate that the extracellular loop regions of YRs have distinctive residues of each species. Expression profile analysis revealed that the grouper Y8b receptor mRNA is primarily expressed in the brain, stomach and intestine, while the grouper Y2 receptor mRNA is primarily expressed in the brain, ovary, liver and heart. Double immunofluorescence analysis determined that the grouper YRs interact with the grouper NPY around the human embryonic kidney 293T cell surface. Furthermore, site-directed mutagenesis in a phage display system revealed that Asp(6.59) might be a common NPY-binding site, while Asp(2.68) of the Y8b receptor and Glu(5.24) of the Y2 receptor could be likely involved in subtype-specific binding. Combining the expression profile and ligand-binding feature, the grouper Y8b receptor could be involved in regulating food intake via the brain-gut axis and the grouper Y2 receptor might play a role in balancing the regulatory activity of the Y8b receptor and participate in metabolism in the liver and ovary.

High-frequency electrical stimulation of cervical vagi reduces airway response to methacholine

AIM: To test whether high-frequency electrical stimulation (HES) of the bilateral cervical vagus nerves reduces the airway responses to methacholine (MCh).

METHODS: Guinea pigs were pretreated with saline (Sal, n = 9) or ovalbumin (Ova, n = 10) aerosol for two weeks (5 min/d, 5 d/wk) and subsequently anesthetized, paralyzed, tracheotomized and artificially ventilated. Both total lung resistance (R_L) and dynamic pulmonary compliance (C_dyn) were recorded. In addition, the effects of vagal low-frequency electrical stimulation (LES, monophasic, 50 Hz) and HES (monophasic and biphasic, 1 and 2.5 kHz) for about 10 s or 2 min on the responses of R_L and C_dyn to MCh aerosol-induced bronchoconstriction were compared in both groups of guinea pigs. In a few guinea pigs, the impact of bivagotomy on the R_L responses to MCh was assessed.

RESULTS: Before MCh challenge, LES, but not HES, significantly increased R_L by about 30% (P < 0.01) and decreased C_dyn by about 20% (P < 0.01) similarly in both groups. MCh aerosol for 2 min elevated R_L and diminished C_dyn more in Ova- than Sal-treated animals (R_L: 313% ± 52% vs 113% ± 17%, P < 0.01; C_dyn: -56% ± 7% vs -21% ± 3%, P < 0.01). During MCh-induced airway constriction, LES further enhanced, but HES decreased R_L and this decrease was greater in Ova- (about 45%) than Sal-treated animals (about 34%, P < 0.01) with little change in cardiovascular activity. On the other hand, LES further reduced whereas HES increased C_dyn more in Ova- (about 20%) than Sal-treated animals (about 13%, P < 0.01). In addition, bivagotomy almost eliminated the R_L and C_dyn responses to MCh.

CONCLUSION: We conclude that vagal HES is able to alleviate the bronchoconstriction induced by MCh in anesthetized guinea pigs, likely via reversible inhibition/blockade of vagal conduction.

Nodose ganglia-modulatory effects on respiration

The key role of the vagus nerves in the reflex control of breathing is generally accepted. Cardiopulmonary vagal receptors and their afferent connection with the medullary respiratory centers secures the proper regulatory feedback. Section of the vagi at the midcervical level interrupts primary vagal reflexes and those due to activation of lung afferents by neuroactive substances. In this context the present review focuses on the reflex contribution of the inferior (nodose) vagal ganglia to the respiratory pattern, considering that this structure contains perikarya of vagal afferent neurons which house neurotransmitters, neuropeptides and neurochemical substances. In experimental animals with removed sensory input from the lungs (midcervical vagotomy) the following evidence was reported. Transient respiratory suppression in the form of apnoea, occurring after systemic injection of serotonin, adenosine triphosphate and anandamide (N-arachidonoyl-ethanolamine-endogenous cannabinoid neurotransmitter), which was abrogated by nodose ganglionectomy. Preserved nodose-NTS connection conditioned respiratory depression affecting the timing component of the breathing pattern evoked by N-6-cyclopentyl-adenosine (CPA) and inhibition of both respiratory constituents induced by NPY. Stimulatory effect of NPY13-36 on tidal volume required nodosal connection. The cardiovascular effects of majority of the tested substances occurred beyond the nodose ganglia (with exclusion of serotonin and anandamide).

Activation of neuropeptide Y(2) receptors exerts an excitatory action on cardio-respiratory variables in anaesthetized rats

The respiratory effects of stimulation of NPYY(2) receptors were studied in spontaneously breathing rats that were either (i) neurally intact and subsequently bilaterally vagotomized in the neck, or (ii) neurally intact and subjected to supranodosal vagotomy or (iii) neurally intact treated with pharmacological blockade of NPY(1-2) receptors. Before neural interventions an intravenous (iv) bolus of the NPYY(2) receptor agonist NPY 13-36 (10 μg/kg) increased breathing rate, tidal volume and mean arterial blood pressure (MAP). Section of the midcervical vagi abrogated NPY 13-36-evoked increase in respiratory rate but had no effect on augmented tidal volume, minute ventilation and blood pressure. Supranodosal vagotomy prevented the increase in tidal volume and slightly reduced the pressor response. Blockade of NPYY(2) receptor with intravenous doses of BIIE 0246 eliminated cardio-respiratory effects of NPY 13-36 injection. BMS 193885 - an antagonist of NPYY(1) receptor-was not effective in abrogating cardio-respiratory response. The present study showed that (i) NPY 13-36 induced stimulation of breathing results from activation of NPYY(2) receptors associated with pulmonary vagal afferentation; (ii) the increase in the frequency of breathing is mediated by midcervical vagi and augmentation of tidal volume relies on the intact supranodosal trunks (iii) the pressor response results from the excitation of NPYY(2) receptors outside of the vagal pathway.

Presynaptic neuropeptide receptors

Presynaptic receptors for four families of neuropeptides will be discussed: opioids, neuropeptide Y, adrenocorticotropic hormone (ACTH), and orexins. Presynaptic receptors for the opioids (micro, delta, kappa, and ORL(1)) and neuropeptide Y (Y(2)) inhibit transmitter release from a variety of neurones, both in the peripheral and central nervous systems. These receptors, which were also identified in human tissue, are coupled to G(i/o) proteins and block voltage-dependent Ca(2+) channels, activate voltage-dependent K(+) channels, and/or interfere with the vesicle release machinery. Presynaptic receptors for ACTH (MC(2) receptors) have so far been identified almost exclusively in cardiovascular tissues from rabbits, where they facilitate noradrenaline release; they are coupled to G(s) protein and act via stimulation of adenylyl cyclase. Presynaptic receptors for orexins (most probably OX(2) receptors) have so far almost exclusively been identified in the rat and mouse brain, where they facilitate the release of glutamate and gamma-aminobutyric acid (GABA); they are most probably linked to G(q) and directly activate the vesicle release machinery or act via a transduction mechanism upstream of the release process. Agonists and antagonists at opioid receptors owe at least part of their therapeutic effects to actions on presynaptic receptors. Therapeutic drugs targeting neuropeptide Y and orexin receptors and presynaptic ACTH receptors so far are not available.

Neuropeptide Y Y2 receptor in health and disease

We briefly survey the current knowledge and concepts regarding structure and function of the neuropeptide Y Y2 receptor and its agonists, especially as related to pharmacology of the receptor and its roles in pathological processes. Specific structural features are considered that could be responsible for the known compartmentalization and participation of the receptor in cell and tissue organization. This is further discussed in relation to changes of levels of the Y2 receptor in pathological conditions (especially in epilepsy and drug abuse), to endocytosis and recycling, and to participation in wound healing, retinopathy and angiogenesis. Properties of the receptor and of Y2 agonists are considered and reviewed in connection to the negative regulation of transmitter release, feeding, mood and social behavior. The possible involvement of the Y2 receptor in diabetes, carcinogenesis and bone formation is also reviewed.

Receptor Subtype-specific Docking of Asp6.59 with C-terminal Arginine Residues in Y Receptor Ligands

Y receptors (YRs) are G protein-coupled receptors whose Y(1)R, Y(2)R, and Y(5)R subtypes preferentially bind neuropeptide Y (NPY) and peptide YY, whereas mammalian Y(4)Rs show a higher affinity for pancreatic polypeptide (PP). Comparison of YR orthologs and paralogs revealed Asp(6.59) to be fully conserved throughout all of the YRs reported so far. By replacing this conserved aspartic acid residue with alanine, asparagine, glutamate, and arginine, we now show that this residue plays a crucial role in binding and signal transduction of NPY/PP at all YRs. Sensitivity to distinct replacements is, however, receptor subtype-specific. Next, we performed a complementary mutagenesis approach to identify the contact site of the ligand. Surprisingly, this conserved residue interacts with two different ligand arginine residues by ionic interactions; although in Y(2)R and Y(5)R, Arg(33) is the binding partner of Asp(6.59), in Y(1)R and Y(4)R, Arg(35) of human PP and NPY interacts with Asp(6.59). Furthermore, Arg(25) of PP and NPY is involved in ligand binding only at Y(2)R and Y(5)R. This suggests significant differences in the docking of YR ligands between Y(1/4)R and Y(2/5)R and provides new insights into the molecular binding mode of peptide agonists at GPCRs. Furthermore, the proposed model of a subtype-specific binding mode is in agreement with the evolution of YRs.

Neuropeptide Y stabilizes body temperature and prevents hypotension in endotoxaemic rats

The on-going high mortality from sepsis motivates continuous research for novel therapeutic strategies. Neuropeptide Y (NPY), a sympathetic neurotransmitter, has been shown to increase survival in experimental septic shock in rats. This protective effect might be due to immunological, cardiovascular or thermoregulatory effects. The aim of this study was to examine the in vivo effect of peripherally administered NPY on body temperature, blood pressure and heart rate in endotoxaemic animals. In order to obtain clinically relevant data, various physiological parameters were monitored in parallel via radio-telemetry in chronically intravenously cannulated, freely behaving rats. Rats received a sublethal bolus of lipopolysaccharide (LPS, 100 microg kg(-1) I.V.) and the three parameters were continuously recorded for 72 h. Endotoxaemic rats showed a long-lasting hypotension, an initial hypothermia (-0.5 degrees C), followed by a prolonged febrile phase (+1.6 degrees C 6 h after endotoxin challenge) associated with a decrease of the circadian rhythm amplitude of temperature. Pretreatment with NPY (160 pmol kg(-1) I.V. over 75 min) prevented hypotension and significantly stabilized body temperature immediately following the application. The febrile phase was effectively reduced for at least 72 h. These telemetrically obtained findings clearly demonstrate that pretreatment with NPY positively influences two life-threatening symptoms in endotoxaemia and might be a future option for a successful clinical treatment regimen.

Effect of remifentanil infusion rate on stress response to the pre-bypass phase of paediatric cardiac surgery

BACKGROUND

Opioids are used routinely to eliminate the stress response in the pre-bypass phase of paediatric cardiac surgery. Remifentanil is a unique opioid allowing a rapidly titratable effect. No data are available regarding a suitable remifentanil dose regimen for obtunding stress and cardiovascular responses to such surgery.

METHODS

We recruited 49 infants and children under 5 yr old who were randomized to receive one of four remifentanil infusion rates (0.25, 1.0, 2.5, or 5.0 micro g kg(-1) min(-1)). Blood samples were obtained at induction, pre-surgery, 5 min after opening the chest, and immediately pre-bypass. Whole blood glucose was measured at all time points while cortisol and neuropeptide Y (NPY) were measured in the first and last samples. Heart rate and arterial pressure were also recorded.

RESULTS

There was a significant increase in whole blood glucose 5 min after opening the chest and pre-bypass (P=0.009, P=0.002) in patients receiving remifentanil 0.25 micro g kg(-1) min(-1), but not in those receiving higher doses. Increased remifentanil dosage was associated with reduced plasma cortisol during surgery (P<0.001). Baseline NPY showed considerable variation and there was no association between pre-bypass NPY and remifentanil dose. There was a significantly higher heart rate at the pre-bypass stage of surgery in the remifentanil 0.25 micro g kg(-1) min(-1) group compared with higher doses (P=0.0006). Four out of five neonates with complex cardiac conditions showed severe bradycardia associated with remifentanil.

CONCLUSIONS

In infants and children under 5 yr, remifentanil infusions of 1.0 micro g kg(-1) min(-1) and greater can suppress the glucose increase and tachycardia associated with the pre-bypass phase of cardiac surgery, while 0.25 micro g kg(-1) min(-1) does not. Remifentanil should be used with caution in neonates with complex congenital heart disease.

Recent developments in our understanding of the physiological role of PP-fold peptide receptor subtypes

The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.

Distribution of neuropeptide Y Y1 and Y2 receptors in the postmortem human heart

In the present study, we present for the first time the presence and distribution of neuropeptide Y (NPY) receptors Y1 and Y2 in the human postmortem heart using specific antibodies raised against extracellular parts of the receptors. A more intensive staining against the Y2 than against the Y1 receptors was detected on both atrial and ventricular cardiomyocytes. Immunoreactivity against both receptors was identified on both conducting fibers and cardiac nerves. More vessels stained positively for the Y2 than for the Y1 receptor, but the Y1 receptors were more abundant in subendocardial than subepicardial vessels of the left ventricular wall.

Pharmacology of neuropeptide Y receptor antagonists. Focus on cardiovascular functions

Neuropeptide Y is one of the most abundant mammalian neuropeptides identified to date. The possible actions of neuropeptide Y, that is co-localized and released with noradrenaline, as a sympathetic co-transmitter has attracted much attention during the last decade. In recent years, several non-peptide antagonists with high subtype selectivity for neuropeptide Y receptors have been introduced. With them, the status of neuropeptide Y as a sympathetic transmitter has been established, and so have profound cardiovascular effects mediated by neuropeptide Y Y(1) and Y(2) receptors. Significant release of neuropeptide Y occurs especially upon stronger sympathetic activation, and recent data suggest that the importance of neuropeptide Y seems enhanced in stress-related cardiovascular disorders. The true significance of neuropeptide Y has thus started to unfold, owing to the presence of the first generation of selective neuropeptide Y receptor antagonists. This review concerns the pharmacology of these agents, what we have learnt from them, and might find out in the future.