neuropeptide-y and Bradycardia

Neuropeptide Y (NPY), a sympathetic neurotransmitter, is highly associated with baroreflex dysfunction and multiple cardiac diseases such as diabetic myocardiopathy. In the present study, we aimed to explore the role of peripheral NPY Y1 receptor (Y1R) and Y2 receptor (Y2R), which are dominantly present in peripheral cardiovascular control, in baroreflex sensitivity (BRS) of streptozotocin (STZ)-induced diabetic rats. Peripheral Y1R and Y2R were antagonized by specific antagonists (BIBP 3226 and BIIE 0246, respectively) from subcutaneously implanted ALZET mini-osmotic pump in STZ-induced diabetic rats for 4 weeks. Then baseline systolic blood pressure, heart rate, cardiac function, BRS, plasma NPY and lipid levels were evaluated. We found that STZ led to increased plasma NPY and lipid level. And the STZ-increased lipid levels were reduced by BIBP 3226 and BIIE 0246. BIBP 3226 ameliorated the aberrant BRS, but had little effect on the impaired cardiac function of the STZ rats. BIIE 0246 alleviated sodium nitroprusside (SNP)-induced but not phenylephrine (PE)-induced aberrant baroreflex control of heart rate in the STZ rats. In addition, BIIE 0246 alleviated the bradycardia, but further impaired cardiac contractility in the STZ rats. These results suggest that peripheral Y1R and Y2R play different roles in STZ-induced impairment of BRS.

Topics: Animals; Arginine; Baroreflex; Benzazepines; Blood Pressure; Bradycardia; Diabetes Mellitus, Experimental; Heart Rate; Myocardial Contraction; Neuropeptide Y; Rats; Receptors, Neuropeptide Y; Streptozocin

The autonomic phenotype of congestive cardiac failure is characterised by high sympathetic drive and impaired vagal tone, which are independent predictors of mortality. We hypothesize that impaired bradycardia to peripheral vagal stimulation following high-level sympathetic drive is due to sympatho-vagal crosstalk by the adrenergic co-transmitters galanin and neuropeptide-Y (NPY). Moreover we hypothesize that galanin acts similarly to NPY by reducing vagal acetylcholine release via a receptor mediated, protein kinase-dependent pathway. Prolonged right stellate ganglion stimulation (10 Hz, 2 min, in the presence of 10 μM metoprolol) in an isolated guinea pig atrial preparation with dual autonomic innervation leads to a significant (p<0.05) reduction in the magnitude of vagal bradycardia (5 Hz) maintained over the subsequent 20 min (n=6). Immunohistochemistry demonstrated the presence of galanin in a small number of tyrosine hydroxylase positive neurons from freshly dissected stellate ganglion tissue sections. Following 3 days of tissue culture however, most stellate neurons expressed galanin. Stellate stimulation caused the release of low levels of galanin and significantly higher levels of NPY into the surrounding perfusate (n=6, using ELISA). The reduction in vagal bradycardia post sympathetic stimulation was partially reversed by the galanin receptor antagonist M40 after 10 min (1 μM, n=5), and completely reversed with the NPY Y(2) receptor antagonist BIIE 0246 at all time points (1 μM, n=6). Exogenous galanin (n=6, 50-500 nM) also reduced the heart rate response to vagal stimulation but had no effect on the response to carbamylcholine that produced similar degrees of bradycardia (n=6). Galanin (500 nM) also significantly attenuated the release of (3)H-acetylcholine from isolated atria during field stimulation (5 Hz, n=5). The effect of galanin on vagal bradycardia could be abolished by the galanin receptor antagonist M40 (n=5). Importantly the GalR(1) receptor was immunofluorescently co-localised with choline acetyl-transferase containing neurons at the sinoatrial node. The protein kinase C inhibitor calphostin (100 nM, n=6) abolished the effect of galanin on vagal bradycardia whilst the protein kinase A inhibitor H89 (500 nM, n=6) had no effect. These results demonstrate that prolonged sympathetic activation releases the slowly diffusing adrenergic co-transmitter galanin in addition to NPY, and that this contributes to the attenuation in vagal bradyca

Topics: Acetylcholine; Animals; Bradycardia; Cholinergic Neurons; Cyclic AMP-Dependent Protein Kinases; Female; Galanin; Gene Expression; Guinea Pigs; Heart; Heart Atria; Neuropeptide Y; Postsynaptic Potential Summation; Protein Kinase C; Receptors, Galanin; Receptors, Neuropeptide Y; Stellate Ganglion; Vagus Nerve

Chronic stress, as a risk factor for cardiovascular diseases, has been reported to result in elevated plasma neuropeptide Y (NPY) and be highly associated with abnormal cardiac autonomic function. This study aimed to explore the effect of NPY on the chronic stress-induced abnormal baroreceptor reflex sensitivity (BRS). Seven types of recognized stressors were used to develop chronic stress rat model. Subcutaneously implanting ALZET mini-osmotic pumps containing NPY were used to evaluate the action of NPY on the stressed male rats. We found that chronic stress showed no influence on baseline systolic blood pressure (SBP) and heart rate (HR), whereas NPY (85 μg for 30 days) could elevate baseline SBP and induce bradycardia in rats intervened by various stimuli. NPY pretreatment could preserve chronic stress-induced decreases in left ventricular systolic pressure (LVSP) and the maximum rate of change in left ventricular pressure in the isovolumic contraction period (+dp/dt(max)) but has shown no effect on left ventricular end diastolic pressure (LVEDP) and the maximum rate of change in left ventricular pressure in the isovolumic relaxation period (-dp/dt(max)). Notably, chronic stress led to baroreflex oversensitivity indicated by the elevated ratio of Δheart rate (HR)/ Δmean arterial blood pressure (MABP) in rats followed by vasoconstrictor (phenylephrine, PE) or vasodilator (sodium nitroprusside, SNP) administration, which was almost completely reversed by NPY pretreatment. The expressions of substance P (SP) and gamma aminobutyric acid A receptor (GABA(A)R) in nucleus tractus solitarius were increased in chronic stress rats, which were counteracted by NPY pretreatment. We conclude that chronic stress-induced baroreflex hypersensitivity could be blocked by NPY pretreatment. Furthermore, the altered expressions of neurotransmitters and receptors in the brainstem might contribute to this process.

Topics: Animals; Baroreflex; Blood Pressure; Body Weight; Bradycardia; Calcitonin Gene-Related Peptide; Dose-Response Relationship, Drug; Heart Rate; Heart Ventricles; Myocardial Contraction; Neuropeptide Y; Nitroprusside; Phenylephrine; Rats; Rats, Wistar; Receptors, GABA-A; RNA, Messenger; Stress, Physiological; Substance P

The co-transmitter neuropeptide Y (NPY), released during prolonged cardiac sympathetic nerve stimulation, can attenuate vagal-induced bradycardia. We tested the hypothesis that NPY reduces acetylcholine release, at similar concentrations to which it attenuates vagal bradycardia, via pre-synaptic Y2 receptors modulating a pathway that is dependent on protein kinase A (PKA) or protein kinase C (PKC). The Y2 receptor was immunofluorescently colocalized with choline acetyl-transferase containing neurons at the guinea pig sinoatrial node. The effect of NPY in the presence of various enzyme inhibitors was then tested on the heart rate response to vagal nerve stimulation in isolated guinea pig sinoatrial node/right vagal nerve preparations and also on (3)H-acetylcholine release from right atria during field stimulation. NPY reduced the heart rate response to vagal stimulation at 1, 3 and 5 Hz (significant at 100 nM and reaching a plateau at 250 nM NPY, p<0.05, n=6) but not to the stable analogue of acetylcholine, carbamylcholine (30, 60 or 90 nM, n=6) which produced similar degrees of bradycardia. The reduced vagal response was abolished by the Y2 receptor antagonist BIIE 0246 (1 microM, n=4). NPY also significantly attenuated the release of (3)H-acetylcholine during field stimulation (250 nM, n=6). The effect of NPY (250 nM) on vagal bradycardia was abolished by the PKC inhibitors calphostin C (0.1 microM, n=5) and chelerythrine chloride (25 microM, n=6) but not the PKA inhibitor H89 (0.5 microM, n=6). Conversely, the PKC activator Phorbol-12-myristate-13-acetate (0.5 microM, n=7) mimicked the effect of NPY and significantly reduced (3)H-acetylcholine release during field stimulation. These results show that NPY attenuates vagal bradycardia via a pre-synaptic decrease in acetylcholine release that appears to be mediated by a Y2 receptor pathway involving modulation of PKC.

Topics: Acetylcholine; Animals; Arginine; Benzazepines; Bradycardia; Carbachol; Choline O-Acetyltransferase; Cyclic AMP-Dependent Protein Kinases; Female; Guinea Pigs; Heart Rate; Immunohistochemistry; Isoquinolines; Neuropeptide Y; Protein Kinase C; Receptors, Neuropeptide Y; Signal Transduction; Sinoatrial Node; Sulfonamides; Vagus Nerve

Neuropeptide Y (NPY) is involved in the regulation of emotionality including fear and anxiety, which modulate autonomic control of cardiovascular function. We therefore investigated the central effects of porcine NPY, selective Y1, Y2 and Y5 receptor agonists and a Y1 receptor antagonist on heart rate (HR) and HR variability in freely moving mice using auditory fear conditioning. Intracerebroventricular (i.c.v.) injections were applied 15 min before the tone-dependent memory test. NPY dose-dependently induced bradycardia associated with decreased HR variability, and blunted the stress-induced tachycardic response. The selective Y1 receptor antagonist BIBO 3304 blocked the NPY- and Y1-receptor agonist-induced suppression of conditioned tachycardia without affecting basal HR. The tachycardia elicited by both conditioned and unconditioned stressor was effectively attenuated by the Y1 receptor agonist. These results suggest a specific contribution of Y1, but not Y2 and Y5 receptors, to modulation of emotional responses most likely unrelated to impairment or modulation of memory. The NPY-induced bradycardia is attributed to not yet characterized NPY receptor subtypes other than Y1, Y2 and Y5, or a complex receptor interaction. In conclusion, NPY mediates central inhibition of sympathetic outflow, potentially coupled with attenuation of parasympathetic tone, i.e., mechanisms that may be associated with the reported anxiolytic action.

Topics: Animals; Arginine; Auditory Perception; Bradycardia; Conditioning, Psychological; Cues; Fear; Heart Rate; Male; Mice; Mice, Inbred C57BL; Neuropeptide Y; Receptors, Neuropeptide Y; Swine

Prejunctional neuropeptide Y (NPY) Y1 receptors on cardiac sympathetic neurons mediate transient inhibition of chronotropic responses in rabbit isolated right atria. The function of these receptors remains speculative. We investigated a possible functional role for these receptors in modulation of the baroreceptor-heart rate (HR) reflex in the conscious rabbit. Mean arterial pressure (MAP) responses to a range of doses of the Y1 receptor agonist [Leu31,Pro34]NPY (1-8 microg/kg, i.v.) were constructed in ganglion-blocked rabbits. After administration of the selective Y1 receptor antagonist GR231118(150 microg/kg, i.v.), two-point [Leu31,Pro34]NPY dose-pressor responses were assessed. Linear regression analysis of the relation between the shift in the [Leu31,Pro34]NPY dose-pressor response lines against time was used as an estimate of the functional half-life of GR231118. GR231118 shifted the two-point [Leu31,Pro34]NPY dose-pressor response relation by 10- to 30-fold. A single estimate of the functional half-life of a bolus dose of GR231118 was 25 +/- 2 min. This determination allowed a steady-state Y1-receptor blockade to be established by a bolus and infusion. In a separate group of rabbits, the baroreceptor-HR reflex was assessed before and 30 min after administration of GR231118 (150 microg/kg bolus, then 150 microg/ kg/h, i.v.). GR231118 caused an initial transient pressor response and bradycardia, followed by a depressor response and a more sustained tachycardia. Infusion of GR231118 had no effect on the baroreceptor-HR reflex. Prejunctional Y1 receptors appear not to mediate a tonic inhibition of cardiac sympathetic neurotransmission in the conscious rabbit during physiological manipulations in MAP. However, activation of postjunctional Y1 receptors by neuronal or circulating NPY may be important in maintenance of vascular tone in the conscious rabbit.

Topics: Animals; Blood Pressure; Bradycardia; Dose-Response Relationship, Drug; Female; Heart Rate; Male; Neuropeptide Y; Peptides, Cyclic; Pressoreceptors; Rabbits; Receptors, Neuropeptide Y; Tachycardia; Time Factors

Diaspirin crosslinked hemoglobin (DCLHb) is a chemically stabilized hemoglobin (Hb) that induces an increase in blood pressure and a decrease of heart rate when injected intravenously in some animals. The mechanism by which DCLHb elicits these hemodynamic effects was studied in pentobarbital-anesthetized, vagotomized rats using a variety of drugs known for their inhibitory action towards endogenous hemodynamically active systems. The hypertensive episode elicited by DCLHb (100 or 400 mg.kg-1) was attenuated in animals pretreated with NG-nitro-L-arginine (inhibitor of nitric oxide synthases) throughout the 30-min period of observation, but it was not reduced in those pretreated with a variety of sympatholytic drugs (e.g., prazosin), atropine, BIBP-3226 (neuropeptide Y antagonist), indomethacin, [1-(beta-mercapto-beta,beta-cyclopentanemethylene propionic acid), 2-(0-methyl) tyrosine]-Arg8 vasopressin (vasopressin antagonist), losartan (angiotensin antagonist), bosentan (endothelin antagonist), or L-arginine-(nitric oxide precursor), compared with control animals. With the exception of propranolol and BIBP-3226, none of the aforenamed inhibitors reduced the amplitude of the bradycardia associated with the pressor effect of DCLHb. These results suggest that: (i) the acute (< 30 min) pressor activity of DCLHb in our animal model requires the presence of an endogenous nitric oxide generating system to be expressed; (ii) the bradycardia elicited by DCLHb might involve the participation of neuropeptide Y and (or) its NPY-1 receptors, but it is unlikely to involve a baroreceptor-mediated vagal reflex, at least in our animal model.

Topics: Animals; Arginine; Aspirin; Blood Pressure; Blood Substitutes; Bradycardia; Enzyme Inhibitors; Hemoglobins; Male; Neuropeptide Y; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y; Vagotomy

1. Neuropeptide Y (NPY) is colocalized with catecholamines in central regions involved in blood pressure regulation and exerts depressor responses in the nucleus tractus solitarius (NTS). Ageing is accompanied by a decline in baroreflex function and a reduction in NPY concentrations in some brain areas. The present study investigated whether the cardiovascular response to NPY microinjection into the NTS and medullary NPY concentrations were conserved in aged rats. 2. Neuropeptide Y (6 pmol in 100 nL) unilaterally injected into the NTS of anaesthetized 3- or 17-month-old male Sprague-Dawley rats produced a prompt 9-10% fall in mean arterial pressure (MAP), which tended to last longer in aged rats. Decreases in heart rate (HR) observed following NPY administration into the NTS were modest but more prolonged than the depressor responses. ANOVA with repeated measures demonstrated no significant effect of age on the MAP or HR response to NPY injection into the NTS. Neuropeptide Y concentrations in the dorsomedial and ventrolateral medulla were not different between the two age groups. 3. Thus, the depressor and bradycardic responses to exogenous NPY administration in the NTS were maintained with age, in keeping with the observation of similar medullary NPY concentrations in adult and aged rats.

Topics: Aging; Animals; Blood Pressure; Bradycardia; Cardiovascular Physiological Phenomena; Cardiovascular System; Heart Rate; Male; Medulla Oblongata; Microinjections; Neuropeptide Y; Rats; Rats, Sprague-Dawley; Solitary Nucleus; Stereotaxic Techniques

Stimulation of the dorsal part of the midbrain periaqueductal gray matter (dPAG) inhibits baroreflex vagal bradycardia (BVB) via a central mechanism. Here we report that the dPAG suppresses vagal bradycardia also by a peripheral mechanism. In chloralose-urethan-anesthetized, beta-blocked rats, the cervical vagus nerve was cut and the distal cut end was electrically stimulated to induce vagal bradycardia (VIB). Sustained electrical stimulation of the dPAG attenuated VIB in a duration-dependent manner but did not affect bradycardia induced by intravenous acetyl-choline (AIB). The dPAG inhibition of VIB was abolished by C1 transection. Intravenous norepinephrine (NE) reduced VIB but did not affect AIB. Both the dPAG and NE inhibitions of VIB were largely attenuated during intravenous prazosin, a selective alpha 1-receptor antagonist. In contrast, BVB provoked by aortic depressor nerve stimulation was remarkably inhibited by a shortly preceding dPAG stimulation, but this inhibition was not affected by C1 transection. Prazosin treatment did reduced the inhibition, but only moderately. In conclusion, the dPAG has a potential ability to suppress VIB by prejunctionally inhibiting acetylcholine release from cardiac vagus nerve terminals via alpha 1-receptors. However, dPAG stimulation first suppresses BVB largely at a central site, leaving a limited fraction of vagal outflow to be inhibited by a prejunctional mechanism operating with long latency.

Topics: Acetylcholine; Animals; Baroreflex; Bradycardia; Electric Stimulation; Male; Mesencephalon; Neural Inhibition; Neuropeptide Y; Norepinephrine; Periaqueductal Gray; Prazosin; Rats; Rats, Wistar; Receptors, Adrenergic, alpha; Vagus Nerve

Neuropeptide Y (NPY) is contained in and coreleased with norepinephrine (NE) from sympathetic nerves innervating vascular and cardiac tissues. The effects of NPY infusion on systemic hemodynamics and cardiac performance were compared with those of NE in conscious and pentobarbital sodium-anesthetized rats. A 10-min infusion of NPY (2 nmol.kg-1.min-1) decreased cardiac index (CI) 20% and stroke volume index (SVI) 9% with increases of 20% in mean arterial pressure (MAP) and 48% in total peripheral resistance (TPR). Conversely, NE (1.0 microgram.kg-1.min-1) increased SVI 14%, MAP 29%, and TRP 26%, with no change in CI. Heart rates decreased similarly (approximately 60 beats/min) but only NE-induced bradycardia was reversible by methylatropine nitrate. In anesthetized rats NPY (0.1 nmol.kg-1.min-1) increased left ventricular end-diastolic pressure (LVEDP) 20 +/- 10 mmHg (means +/- SD, n = 7) and decreased dP/dt by 8 +/- 6%. NE (0.07 microgram.kg-1.min-1) produced an equivalent pressor response, however, dP/dt rose 22 +/- 10% whereas LVEDP increased significantly less than with NPY. Thus NPY is a potent vasoconstrictor exerting similar effects to NE on MAP and TPR but, unlike NE, possesses negative inotropic and chronotropic activity.

Topics: Animals; Atropine Derivatives; Blood Pressure; Bradycardia; Depression, Chemical; Heart Rate; Hemodynamics; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Inbred Strains; Vasoconstriction

Topics: Animals; Blood Pressure; Bradycardia; Brain; Feeding Behavior; Heart Rate; Hypotension; Injections, Intraventricular; Male; Neuropeptide Y; Rats; Rats, Inbred Strains; Respiration