Neuropeptide Y Y1 receptors are involved in the vasoconstriction caused by human sympathetic nerve stimulation

Relation of plasma neuropeptide-Y with myocardial function and infarct severity in acute ST-elevation myocardial infarction

BACKGROUND

Acute myocardial infarction is associated with the release of the co-transmitter neuropeptide-Y (NPY). NPY acts as a potent vasoconstrictor and is associated with microvascular dysfunction after ST-elevation myocardial infarction (STEMI). This study comprehensively evaluated the association of plasma NPY with myocardial function and infarct severity, visualized by cardiac magnetic resonance (CMR) imaging, in STEMI patients revascularized by primary percutaneous coronary intervention (PCI).

METHODS

In this observational study, we included 260 STEMI patients enrolled in the prospective MARINA-STEMI (NCT04113356) study. Plasma NPY concentrations were measured by an immunoassay 24h after PCI from peripheral venous blood samples. Left ventricular ejection fraction (LVEF), global longitudinal strain (GLS), infarct size (IS) and microvascular obstruction (MVO) were determined using CMR imaging.

RESULTS

Median plasma concentrations of NPY were 70 [interquartile range (IQR):35-115] pg/ml. NPY levels above median were significantly associated with lower LVEF (48%vs.52%, p=0.004), decreased GLS (-8.8%vs.-12.6%, p<0.001) and larger IS (17%vs.13%, p=0.041) in the acute phase after infarction as well as after 4 months (LVEF:50%vs.52%, p=0.030, GLS:-10.5vs.-12.9,p<0.001,IS:13%vs.10%,p=0.011). In addition, NPY levels were significantly related to presence of MVO (58%vs.52%, p=0.041). Moreover, in multivariable linear regression analysis, NPY remained significantly associated with all investigated CMR parameters (LVEF:p<0.001,GLS:p<0.001,IS:p=0.003,MVO:p=0.042) independent of other established clinical variables including high-sensitivity cardiac troponin T, pre-interventional TIMI flow 0 and left anterior descending artery as culprit lesion location.

CONCLUSION

High plasma levels of NPY, measured 24h after STEMI, were independently associated with lower LVEF, decreased GLS, larger IS as well as presence of MVO, indicating plasma NPY as a novel clinical risk marker post STEMI.

Splanchnic Nerve Modulation Effects on Surrogate Measures of Venous Capacitance

Background Splanchnic nerve modulation (SNM) is an emerging procedure to reduce cardiac filling pressures in heart failure. Although the main contributor to reduction in cardiac preload is thought to be increased venous capacitance in the splanchnic circulation, supporting evidence is limited. We examined changes in venous capacitance surrogates pre- and post-SNM. Methods and Results This is a prespecified analysis of a prospective, open-label, single-arm interventional study evaluating the effects of percutaneous SNM with ropivacaine in chronic heart failure with elevated filling pressures at rest and with exercise. Patients underwent cardiopulmonary exercise testing with invasive hemodynamic assessment pre- and post-SNM. Blood pressure changes with modified Valsalva maneuver and hemoconcentration, pre- and post-SNM were compared using a repeated measures model. Inferior vena cava diameter and collapsibility (>50% decrease in size with inspiration), and presence of bendopnea pre- and post-SNM were also compared. Fifteen patients undergoing SNM (age 58 years, 47% women, 93% with left ventricular ejection fraction ≤35%) were included. After SNM, changes in systolic blood pressure during Valsalva (peak-to-trough) were greater (41 versus 48 mm Hg, P=0.025). Exercise-induced hemoconcentration was unchanged (0.63 versus 0.43 g/dL, P=0.115). Inferior vena cava diameter was reduced (1.59 versus 1.30 cm, P=0.034) with higher collapsibility (33% versus 73%, P=0.014). Bendopnea was less (47% versus 13%, P=0.025). Conclusions SNM resulted in increased venous capacitance, associated decreased cardiac preload, and decreased bendopnea. Minimally invasive measures of venous capacitance could serve as markers of successful SNM. Long-term effects of SNM on venous capacitance warrant further investigation for heart failure management. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03453151.

The Role of Neuropeptide Y in Cardiovascular Health and Disease

Neuropeptide Y (NPY) is an abundant sympathetic co-transmitter, widely found in the central and peripheral nervous systems and with diverse roles in multiple physiological processes. In the cardiovascular system it is found in neurons supplying the vasculature, cardiomyocytes and endocardium, and is involved in physiological processes including vasoconstriction, cardiac remodeling, and angiogenesis. It is increasingly also implicated in cardiovascular disease pathogenesis, including hypertension, atherosclerosis, ischemia/infarction, arrhythmia, and heart failure. This review will focus on the physiological and pathogenic role of NPY in the cardiovascular system. After summarizing the NPY receptors which predominantly mediate cardiovascular actions, along with their signaling pathways, individual disease processes will be considered. A thorough understanding of these roles may allow therapeutic targeting of NPY and its receptors.

Evidence for a functional vasoconstrictor role for ATP in the human cutaneous microvasculature

NEW FINDINGS

What is the central question of this study? In young adults, about half of the cold-related reduction in skin blood flow during cold exposure is mediated by noradrenaline, while the remainder is attributable to other substances co-released with noradrenaline that have yet to be identified. What is the main finding and its importance? Purinergic receptor blockade blunted the vasoconstriction response to whole-body cooling and to intradermal administration of tyramine. These results indicate that ATP is necessary to vasoconstrict blood vessels in the skin adequately and prevent heat loss in a cold environment. Noradrenaline is responsible for eliciting ∼60% of the reflex cutaneous vasoconstriction (VC) response in young adults, while the remainder is attributable to one or more unidentified co-released sympathetic adrenergic neurotransmitter(s). Inconsistent evidence has placed neuropeptide Y in this role; however, other putative cotransmitters have yet to be tested. We hypothesize that ATP contributes to the reflex cutaneous VC response. Two protocols were conducted in young adults (n = 10); both involved the placement of three microdialysis probes in forearm skin and whole-body cooling (skin temperature = 30.5°C). In protocol 1, the following solutions were infused: (i) lactated Ringer solution (control); (ii) 10 mm l-NAME; and (iii) purinergic receptor blockade with 1 mm suramin plus l-NAME. In protocol 2, the following solutions were infused: (i) lactated Ringer solution; (ii) suramin plus l-NAME; and (iii) suramin plus l-NAME plus adrenoreceptor blockade with 5 mm yohimbine plus 1 mm propranolol. Laser Doppler flux (LDF) was measured over each microdialysis site, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP) and expressed as percentage changes from baseline (%ΔCVC_BASELINE ). l-NAME was used to block the vasodilatory influence of ATP and unmask the P₂ X-mediated VC response to exogenous ATP infusion (-21 ± 6%ΔCVC_BASELINE ). During cooling, the VC response (control, -39 ± 8%ΔCVC_BASELINE ) was attenuated at the suramin site (-21 ± 4%ΔCVC_BASELINE ) and further blunted with combined adrenoreceptor blockade (-9 ± 3%ΔCVC_BASELINE ; P < 0.05). Compared with the control site (-22 ± 5%ΔCVC_BASELINE ), suramin inhibited pharmacologically induced VC to tyramine (-12 ± 6%ΔCVC_BASELINE ; P < 0.05), which displaces adrenergic neurotransmitters from axon terminals. These data indicate that ATP contributes to the cutaneous VC response in humans.

Electrical muscle stimulation in thomboprophylaxis: review and a derived hypothesis about thrombogenesis-the 4th factor

INTRODUCTION

Electrical muscle stimulation (EMS) is an FDA-approved thromboprophylactic method. Thrombus pathogenesis is considered to depend on factors related to components of the vessel wall, the velocity of blood, and blood consistency-collectively known as, the Virchow's triad.

OBJECTIVE

The testimony supporting the thromboprophylactic effects of the EMS is reviewed. An emphasis is placed on the fact that, EMS has demonstrated, in certain circumstances, an efficacy rate that cannot be fully explained by the Virchow's triad; also that, in reviewing relevant evidence and the theorized pathophysiological mechanisms, several findings collectively point to a potentially missed point. Remarkably, venous thromboembolic disease (VTE) is extremely more common in the lower versus the upper extremities even when the blood velocities equalize; EMS had synergistic effects with intermittent compressive devices, despite their presumed identical mechanism of action; sleep is not thrombogenic; non-peroperative EMS is meaningful only if applied ≥5 times daily; neural insult increases VTEs more than the degree expected by the hypomobility-related blood stasis; etc. These phenomena infer the presence of a 4th thrombogenetic factor: neural supply to the veins provides direct antithrombic effects, by inducing periodic vessel diameter changes and/or by neuro-humoral, chemically acting factors. EMS may stimulate or substitute the 4th factor. This evidence-based hypothesis is analyzed.

CONCLUSION

A novel pathophysiologic mechanism of thrombogenesis is supported; and, based on this, the role of EMS in thromboprophylaxis is expanded. Exploration of this mechanism may provide new targets for intervention.

Elevated levels of neuropeptide Y in preeclampsia: A pilot study implicating a role for stress in pathogenesis of the disease

OBJECTIVE

To determine if preeclampsia (PE) is associated with dysregulation of the neuropeptide Y (NPY) system.

METHODS

The study enrolled 114 subjects either with normal pregnancy (NP) or with PE. Systolic blood pressure (SBP) was collected from patients using a standard sphygmomanometer. The PE patients were divided into two groups based on the gestational age (GA) at delivery - placental PE (PLPE, GA <34 weeks) or maternal PE (MTPE, GA ≥34 weeks). NPY was measured in platelet rich plasma (PRP), platelet poor plasma (PPP) and in the serum of NP and PE patients utilizing radioimmunoassay. Serum levels of soluble fms-like tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) were measured in NP and PE subjects by ELISA.

RESULTS

SBP was higher in PE compared to NP. Circulating NPY in serum and PRP, as well as NPY content per 100,000 platelets, but not its concentrations in PPP, were elevated in PE, as compared to NP. The highest NPY concentrations were observed in sera and PRP of patients with MTPE. PE patients had also elevated levels of sFlt-1, as compared to NP, although no difference between PLPE and MTPL groups were observed. There was no increase in P1GF in PE patients.

CONCLUSION

Systemic NPY is elevated in PE patients, as compared to NP. This increase is observed in blood fractions containing platelets, suggesting accumulation of the peptide in these cells. NPY concentrations are particularly high in patients with MTPE, underlying differences in etiology between PLPE and MTPE. Our study implicates NPY as a potential target in antihypertensive therapies for PE patients.

Sympathetic control of reflex cutaneous vasoconstriction in human aging

This Synthesis highlights a series of recent studies that has systematically interrogated age-related deficits in cold-induced skin vasoconstriction. In response to cold stress, a reflex increase in sympathetic nervous system activity mediates reductions in skin blood flow. Reflex vasoconstriction during cold exposure is markedly impaired in aged skin, contributing to the relative inability of healthy older adults to maintain core temperature during mild cold stress in the absence of appropriate behavioral thermoregulation. This compromised reflex cutaneous vasoconstriction in healthy aging can occur as a result of functional deficits at multiple points along the efferent sympathetic reflex axis, including blunted sympathetic outflow directed to the skin vasculature, reduced presynaptic neurotransmitter synthesis and/or release, and altered end-organ responsiveness at several loci, in addition to potential alterations in afferent thermoreceptor function. Arguments have been made that the relative inability of aged skin to appropriately constrict is due to the aging cutaneous arterioles themselves, whereas other data point to the neural circuitry controlling those vessels. The argument presented herein provides strong evidence for impaired efferent sympathetic control of the peripheral cutaneous vasculature during whole body cold exposure as the primary mechanism responsible for attenuated vasoconstriction.

Vas deferens neuro-effector junction: from kymographic tracings to structural biology principles

The vas deferens is a simple bioassay widely used to study the physiology of sympathetic neurotransmission and the pharmacodynamics of adrenergic drugs. The role of ATP as a sympathetic co-transmitter has gained increasing attention and furthered our understanding of its role in sympathetic reflexes. In addition, new information has emerged on the mechanisms underlying the storage and release of ATP. Both noradrenaline and ATP concur to elicit the tissue smooth muscle contractions following sympathetic reflexes or electrical field stimulation of the sympathetic nerve terminals. ATP and adenosine (its metabolic byproduct) are powerful presynaptic regulators of co-transmitter actions. In addition, neuropeptide Y, the third member of the sympathetic triad, is an endogenous modulator. The peptide plus ATP and/or adenosine play a significant role as sympathetic modulators of transmitter's release. This review focuses on the physiological principles that govern sympathetic co-transmitter activity, with special interest in defining the motor role of ATP. In addition, we intended to review the recent structural biology findings related to the topology of the P2X1R based on the crystallized P2X4 receptor from Danio rerio, or the crystallized adenosine A2A receptor as a member of the G protein coupled family of receptors as prototype neuro modulators. This review also covers structural elements of ectonucleotidases, since some members are found in the vas deferens neuro-effector junction. The allosteric principles that apply to purinoceptors are also reviewed highlighting concepts derived from receptor theory at the light of the current available structural elements. Finally, we discuss clinical applications of these concepts.

NO production and eNOS phosphorylation induced by epinephrine through the activation of beta-adrenoceptors

Epinephrine plays a key role in the control of vasomotor tone; however, the participation of the NO/cGMP pathway in response to beta-adrenoceptor activation remains controversial. To evaluate the involvement of the endothelium in the vascular response to epinephrine, we assessed NO production, endothelial NO synthase phosphorylation, and tissue accumulation of cGMP in the perfused arterial mesenteric bed of rat. Epinephrine elicited a concentration-dependent increase in NO (EC(50) of 45.7 pM), which was coupled to cGMP tissue accumulation. Both NO and cGMP production were blocked by either endothelium removal (saponin) or NO synthase inhibition (N(omega)-nitro-L-arginine). Blockade of beta(1)- and beta(2)-adrenoceptors with 1 microM propranolol or beta(3)-adrenoceptor with 10 nM SR 59230A displaced rightward the concentration-NO production curve evoked by epinephrine. Selective stimulation of beta(1)-, beta(2)-, or beta(3)-adrenoceptors also resulted in NO and cGMP production. Propranolol (1 microM) inhibited the rise in NO induced by isoproterenol or the beta(2)-adrenoceptor agonists salbutamol, terbutaline, or fenoterol. Likewise, 10 nM SR 59230A reduced the effects of the beta(3)-adrenoceptor agonists BRL 37344, CGP 12177, SR 595611A, or pindolol. The NO production induced by epinephrine and BRL 37344 was associated with the activation of the phosphatidylinositol 3-kinase/Akt pathway and phosphorylation of eNOS in serine 1177. In addition, in anaesthetized rats, bolus administration of isoproterenol, salbutamol, or BRL 37344 produced NO-dependent reductions in systolic blood pressure. These findings indicate that beta(1)-, beta(2)-, and beta(3)-adrenoceptors are coupled to the NO/cGMP pathway, highlighting the role of the endothelium in the vasomotor action elicited by epinephrine and related beta-adrenoceptor agonists.

Splanchnic and systemic vasodilation: the experimental models

Experimental models are a sine qua non condition for unraveling the specific components and mechanisms contributing to vascular dysfunction and arterial vasodilation in portal hypertension. Moreover, a careful selection of the type of animal model, vascular bed, and methodology is crucial for any investigation of this issue. In this review, some critical aspects related to experimental models in portal hypertension and the techniques applied are highlighted. In addition, a detailed summary of the mechanisms of arterial vasodilation in portal hypertension is presented. First, humoral and endothelial vasodilators, predominantly nitric oxide but also carbon monoxide and endothelium-derived hyperpolarizing factor, and others are discussed. Second, time course and potential stimuli triggering and/or perpetuating splanchnic vasodilation are delineated. Finally, a brief general overview of vascular smooth muscle signaling sets the stage for a discussion on cotransmission, receptor desensitization, and the observed impairment in vasoconstrictor-induced smooth muscle contraction in the splanchnic and systemic circulation during portal hypertension.

In vivo mechanisms of cutaneous vasodilation and vasoconstriction in humans during thermoregulatory challenges

This review focuses on the neural and local mechanisms that have been demonstrated to effect cutaneous vasodilation and vasoconstriction in response to heat and cold stress in vivo in humans. First, our present understanding of the mechanisms by which sympathetic cholinergic nerves mediate cutaneous active vasodilation during reflex responses to whole body heating is discussed. These mechanisms include roles for cotransmission as well as nitric oxide (NO). Next, the mechanisms by which sympathetic noradrenergic nerves mediate cutaneous active vasoconstriction during whole body cooling are reviewed, including cotransmission by neuropeptide Y (NPY) acting through NPY Y1 receptors. Subsequently, current concepts for the mechanisms that effect local cutaneous vascular responses to direct skin warming are examined. These mechanisms include the roles of temperature-sensitive afferent neurons as well as NO in causing vasodilation during local heating of skin. This section is followed by a review of the mechanisms that cause local cutaneous vasoconstriction in response to direct cooling of the skin, including the dependence of these responses on intact sensory and sympathetic, noradrenergic innervation as well as roles for nonneural mechanisms. Finally, unresolved issues that warrant further research on mechanisms that control cutaneous vascular responses to heating and cooling are discussed.

Enhanced Y1-receptor-mediated vasoconstrictive action of neuropeptide Y (NPY) in superior mesenteric arteries in portal hypertension

BACKGROUND/AIMS

Vascular hyporeactivity to catecholamines contributes to arterial vasodilation and hemodynamic dysregulation in portal hypertension. Neuropeptide Y (NPY) is a sympathetic neurotransmitter facilitating adrenergic vasoconstriction via Y1-receptors on the vascular smooth muscle. Therefore, we investigated its role for vascular reactivity in the superior mesenteric artery (SMA) of portal vein ligated (PVL) and sham operated rats.

METHODS

In vitro perfused SMA vascular beds of rats were tested for the cumulative dose-response to NPY dependent on the presence and level of alpha1-adrenergic vascular tone (methoxamine MT: 0.3-10 microM). Moreover, the effect of NPY (50 nM) on vascular responsiveness to alpha1-adrenergic stimulation (MT: 0.3-300 microM) was evaluated. Y1-receptor function was tested by Y1-selective inhibition using BIBP-3226 (1 microM).

RESULTS

NPY dose-dependently and endothelium-independently enhanced MT-pre-constriction in SMA. This potentiation was increasingly effective with increasing adrenergic pre-stimulation and being more pronounced in PVL rats as compared to sham rats at high MT concentrations. NPY enhanced vascular contractility only in PVL rats correcting the adrenergic vascular hyporeactivity. Y1-receptor inhibition completely abolished NPY-evoked vasoconstrictive effects.

CONCLUSIONS

NPY endothelium-independently potentiates adrenergic vasoconstriction via Y1-receptors being more pronounced in portal hypertension improving mesenteric vascular contractility and thereby correcting the splanchnic vascular hyporeactivity. This makes NPY a superior vasoconstrictor counterbalancing arterial vasodilation in portal hypertension.

Sympathetic co-transmission: the coordinated action of ATP and noradrenaline and their modulation by neuropeptide Y in human vascular neuroeffector junctions

The historical role of noradrenaline as the predominant sympathetic neurotransmitter in vascular neuroeffector junctions has matured to include ATP and the modulator action of neuropeptide Y (NPY). Numerous studies with isolated blood vessels rings demonstrate the presence of key enzymes responsible for the synthesis of ATP, noradrenaline and NPY, their co-storage, and their electrically evoked release from sympathetic perivascular nerve terminals. Functional assays coincide to demonstrate the integral role of these neurochemicals in sympathetic reflexes. In addition, the detection of the diverse receptor populations for ATP, noradrenaline and NPY in blood vessels, either in the smooth muscle, endothelial cells or nerve endings, further contribute to the notion that sympathetic vascular reflexes encompass the orchestrated action of the noradrenaline and ATP, and their modulation by NPY. The future clinical opportunities of sympathetic co-transmission in the control of human cardiovascular diseases will be highlighted.

Altered neurotransmitter control of reflex vasoconstriction in aged human skin

Cutaneous vasoconstriction (VC) in response to cooling is attenuated in older humans; however, mechanisms underlying this functional decline remain unclear. The present study tested the hypothesis that the contributions of noradrenaline (NA) and sympathetic cotransmitters to reflex-mediated cutaneous VC are altered with age. In 11 young (18-26 years) and 11 older (61-77 years) men and women, forearm skin blood flow was monitored at three sites using laser Doppler flowmetry (LDF) while mean skin temperature was lowered from 34 to 30.5 degrees C using a water-perfused suit. Cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was expressed as percentage change from baseline (% DeltaCVC(base)). Solutions of yohimbine + propranolol (Y + P), bretylium tosylate (BT), and lactated Ringer solution were infused via intradermal microdialysis at each LDF site to antagonize alpha- and beta-adrenoceptors, block sympathetic release of NA and cotransmitters, and act as control, respectively. During cooling, VC was attenuated at the control site in older subjects compared to young subjects (-16 +/- 3 versus-34 +/- 4% DeltaCVC(base), P < 0.001). Y + P attenuated VC in young subjects (-13 +/- 8% DeltaCVC(base), P < 0.001 versus control) and abolished VC in older subjects (0 +/- 3% DeltaCVC(base), P > 0.9 versus baseline). BT completely blocked VC in both age groups. Cutaneous VC in young subjects is mediated by both NA and sympathetic cotransmitter(s); however, reflex VC in aged skin is attenuated compared to young and appears to be mediated solely by NA.

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.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Effects of a selective neuropeptide Y Y(1) receptor antagonist BIBP 3226 on double peaked vasoconstrictor responses to periarterial nerve stimulation in canine splenic arteries

The periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient constriction (first peak) followed by a prolonged response (second peak) in the isolated, perfused canine splenic artery. At low frequencies (1 and 4 Hz), a neuropeptide Y (NPY) Y(1) receptor antagonist BIBP 3226 (0.1-1 microM) produced a dose-dependent inhibitory effect on the second peak, but did not modify the first peak. At a high frequency (10 Hz), 1 microM BIBP 3226 induced a slight, but significant inhibition on both the first and second peaked responses. At a low frequency (1 Hz), the first peak was not influenced by blockade of alpha(1)-adrenoceptors or NPY Y(1) receptors with prazosin (0.1 microM) or BIBP 3226 (1 microM), respectively, but abolished by P2X receptor desensitization with alpha,beta-methylene ATP (alphabeta-m ATP, 1 microM). At a high frequency (10 Hz), the first peak was mostly inhibited by alphabeta-m ATP and partially by prazosin and BIBP 3226. On the other hand, the second peak at a low frequency was largely decreased by BIBP 3226 and partially by prazosin and alphabeta-m ATP, whereas at a high frequency, it was largely attenuated by prazosin and partially by alphabeta-m ATP and BIBP 3226. The results suggest that at a low frequency, the firstly transient constriction of double peaked responses is mainly induced via an activation of P2X-receptors, whereas at a high frequency, it is mostly mediated by the P2X-receptors, and partially by alpha(1)-receptors and NPY Y(1)-receptors. The secondary prolonged vasoconstriction at frequencies used is predominantly mediated via both alpha(1)-receptor and NPY Y(1) receptor activations, and in part by P2X-receptors. Furthermore, an activation of NPY Y(1) receptors may play an important role in evoking the prolonged vasoconstrictor response to longer pulse trains of stimulation at a low frequency, whereas an alpha(1)-adrenoceptor activation exerts a main vasomotor effect for the prolonged response at a high frequency.

BIIE0246, a potent and highly selective non-peptide neuropeptide Y Y(2) receptor antagonist

1. BIIE0246, a newly synthesized non-peptide neuropeptide Y (NPY) Y(2) receptor antagonist, was able to compete with high affinity (8 to 15 nM) for specific [(125)I]PYY(3 - 36) binding sites in HEK293 cells transfected with the rat Y(2) receptor cDNA, and in rat brain and human frontal cortex membrane homogenates. 2. Interestingly, in rat brain homogenates while NPY, C2-NPY and PYY(3 - 36) inhibited all specific [(125)I]PYY(3 - 36) labelling, BIIE0246 failed to compete for all specific binding suggesting that [(125)I]PYY(3 - 36) recognized, in addition to the Y(2) subtype, another population of specific NPY binding sites, most likely the Y(5) receptor. 3. Quantitative receptor autoradiographic data confirmed the presence of [(125)I]PYY(3 - 36)/BIIE0246-sensitive (Y(2)) and-insensitive (Y(5)) binding sites in the rat brain as well as in the marmoset monkey and human hippocampal formation. 4. In the rat vas deferens and dog saphenous vein (two prototypical Y(2) bioassays), BIIE0246 induced parallel shifts to the right of NPY concentration-response curves with pA(2) values of 8.1 and 8.6, respectively. In the rat colon (a Y(2)/Y(4) bioassay), BIIE0246 (1 microM) completely blocked the contraction induced by PYY(3 - 36), but not that of [Leu(31), Pro(34)]NPY (a Y(1), Y(4) and Y(5) agonist) and hPP (a Y(4) and Y(5) agonist). Additionally, BIIE0246 failed to alter the contractile effects of NPY in prototypical Y(1) in vitro bioassays. 5. Taken together, these results demonstrate that BIIE0246 is a highly potent, high affinity antagonist selective for the Y(2) receptor subtype. It should prove most useful to establish further the functional role of the Y(2) receptor in the organism.

Role of NPY Y1 receptors in cardiovascular control in the conscious rabbit

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.

Rise in endothelium-derived NO after stimulation of rat perivascular sympathetic mesenteric nerves

To evaluate whether sympathetic activity induces nitric oxide (NO) production, we perfused the rat arterial mesenteric bed and measured luminally accessible norepinephrine (NE), NO, and cGMP before, during, and after stimulation of perivascular nerves. Electrical stimulation (1 min, 30 Hz) raised perfusion pressure by 97 +/- 7 mmHg, accompanied by peaks of 23 +/- 3 pmol NE, 445 +/- 48 pmol NO, and 1 pmol cGMP. Likewise, perfusion with 10 microM NE induced vasoconstriction coupled to increased NO and cGMP release. Electrically elicited NO release depended on stimulus frequency and duration. Endothelium denudation with saponin abolished the NO peak without changing NE release. Inhibition of NO synthase with 100 microM N(omega)-nitro-L-arginine reduced basal NO and cGMP release and blocked the electrically stimulated and exogenous NE-stimulated NO peak while enhancing vasoconstriction. Blocking either sympathetic exocytosis with 1 microM guanethidine or alpha1-adrenoceptors with 30 nM prazosin abolished the electrically evoked vasoconstriction and NO release. alpha2-Adrenoceptor blockade with 1 microM yohimbine reduced both vasoconstriction and NO peak while increasing NE release. In summary, sympathetically released NE induces vasoconstriction, which triggers a secondary release of endothelial NO coupled to cGMP production.

The involvement of neuropeptide Y Y1 receptors in the blood pressure baroreflex: studies with BIBP 3226 and BIBO 3304

To ascertain the role of the neuropeptide Y Y1 receptors in the vascular manifestations of the sympathetic baroreflex, 10-s bilateral carotid occlusions were performed in anesthetized cats; systemic blood pressure was monitored continually. This maneuver rose systolic blood pressure in 23 +/- 2 mmHg. Following 100 microg/kg BIBP 3226 or BIBO 3304 i.v., the increase in blood pressure elicited by the occlusions was only 14 +/- 1 and 15 mmHg, respectively. Both BIBP 3226 and BIBO 3304 displaced significantly 5.5 fold rightward the pressor dose-response curve elicited by exogenous neuropeptide Y, without altering the norepinephrine curve. Prazosin (10 microg/kg) reduced the pressor response elicited by the carotid occlusion to 12 +/- 4 mmHg. The simultaneous administration of BIBP 3226 plus prazosin rose the systemic blood pressure following the occlusion only 9 +/- 2 mmHg, supporting the involvement of neuropeptide Y in vascular sympathetic reflexes.

Adenosine 5'-triphosphate and neuropeptide Y are co-transmitters in conjunction with noradrenaline in the human saphenous vein

1. Human saphenous veins were used to assess the cooperative participation of adenosine 5-triphosphate (ATP), neuropeptide Y (NPY), and noradrenaline (NA) in the vasomotor responses elicited following electrical depolarization of the perivascular nerve terminals. Rings from recently dissected human biopsies were mounted to record isometric muscular contractions; the motor activity elicited in the circular muscle layer following electrical depolarization (2.5-20 Hz, 50 V, 0.5 msec) were recorded. 2. Incubation of the biopsies with either 100 nM tetrodotoxin (TTX) or 1 microM guanethidine abolished the vasomotor response elicited by electrical nerve depolarization. The independent application of either ATP or NA to vein rings induced concentration-dependent contractions. 3. Tissue incubation with 30 microM suramin or 10 nM prazosin produced 10 fold rightward displacements of the alpha,beta-methylene ATP and NA concentration-response curves respectively. NPY contracted a limited number of biopsies, the vasoconstriction elicited was completely blocked by 1 microM BIBP 3226. A 5 min incubation of the biopsies with 10-100 nM NPY synergized, in a concentration-dependent fashion, both the ATP and the ATP analogue-induced contractions. Likewise, tissue preincubation with 10 nM NPY potentiated the vasomotor responses evoked with 20-60 nM NA. 4. Neither suramin, BIBP 3226, nor prazosin was individually able to significantly modify the derived frequency-tension curves. In contrast, the co-application of 30 microM suramin and 10 nM prazosin or 30 microM suramin and 1 microM BIBP 3226, elicited a significant (P<0.01) downward displacement of the respective frequency-tension curves. 5. The simultaneous application of the three antagonists-30 microM suramin, 1 microM BIBP 3226 and 10 nM prazosin-caused a significantly greater displacement of the frequency-tension curve than that achieved in experiments using two of these antagonists. 6. Electrically-evoked vasomotor activity is blocked to a larger extent by tissue incubation with 2.5 microM chloroethylclonidine and 30 microM suramin rather than with 10 nM 5 methyl urapidil and 30 microM suramin. As a result, the alpha1-adrenoceptor involved in the vasomotor activity has tentatively been associated with the alpha1B adrenoceptor family subtype. 7. Results support the physiological role of ATP in sympathetic neurotransmission. The present results are consistent with the working hypothesis that human sympathetic vasomotor reflexes involve the coordinated motor action of ATP, NPY, and NA acting on vascular smooth muscle cells. The present results support the concept of sympathetic co-transmission in the human saphenous vein.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Increased neuropeptide Y pressor activity in Goldblatt hypertensive rats: in vivo studies with BIBP 3226

Nanomoles of neuropeptide Y (NPY) and noradrenaline (NA), administered i.v. to pentobarbital-anesthetized rats, caused nearly equipotent dose-dependent pressor responses in normotensive rats. However, in renovascular Goldblatt hypertensive rats, the dose-response curves for both NPY and NA were significantly displaced to the left, approximately threefold. Intravenous administration of BIBP 3226 (30-180 microg/kg) did not consistently lower blood pressure, per se, but did evoke competitive antagonism of the NPY pressor response in both rat populations. The magnitude of the NPY antagonism evoked by BIBP 3226 was comparable in normotensive and hypertensive rats. The absence of NA antagonism demonstrates the selectivity of the BIBP 3226 blockade.