Splanchnic and renal vasoconstrictor and metabolic responses to neuropeptide Y in resting and exercising man

Neuropeptide Y and measures of stress in a longitudinal study of women with the fibromyalgia syndrome

OBJECTIVES

Neuropeptide Y is associated with stress in animal and human laboratory studies. However, data from clinical studies are scarce and no clinical longitudinal studies have been published. The aim of this clinical study was to assess the possible association between changes in the levels of pain, depression, and stress measures, on the one hand, and plasma neuropeptide Y levels, on the other.

METHODS

Forty-four women with the fibromyalgia syndrome were exposed to a Cognitive Behavioral Therapy intervention. Levels of the plasma neuropeptide Y as well as pain, depression, and stress measures were obtained at the start and at the end of the intervention, and after a further six month follow-up. Based on these data, a before-and-after analysis was performed.

RESULTS

Almost all measures of pain, depression, and stress improved during the study; specifically, variables measuring life control (coping), depression, and stress-related time urgency improved significantly. Moreover, during the same time period, the mean plasma neuropeptide Y level was reduced from 93.2 ± 38.8 fmol/mL before the Cognitive Behavioral Therapy to 75.6 ± 42.9 fmol/mL (p<0.001) at the end of the study.

CONCLUSIONS

After exposure to a Cognitive Behavioral Therapy intervention, levels of most of the pain, depression, and stress measures improved, half of them significantly, as did the levels of neuropeptide Y. This circumstance indicates a possible functional relationship between pain-depression-stress and neuropeptide Y.

Renal gluconeogenesis: an underestimated role of the kidney in systemic glucose metabolism

Glucose levels are tightly regulated at all times. Gluconeogenesis is the metabolic pathway dedicated to glucose synthesis from non-hexose precursors. Gluconeogenesis is critical for glucose homoeostasis, particularly during fasting or stress conditions. The renal contribution to systemic gluconeogenesis is increasingly recognized. During the post-absorptive phase, the kidney accounts for ∼40% of endogenous gluconeogenesis, occurring mainly in the kidney proximal tubule. The main substrate for renal gluconeogenesis is lactate and the process is regulated by insulin and cellular glucose levels, but also by acidosis and stress hormones. The kidney thus plays an important role in the maintenance of glucose and lactate homoeostasis during stress conditions. The impact of acute and chronic kidney disease and proximal tubular injury on gluconeogenesis is not well studied. Recent evidence shows that in both experimental and clinical acute kidney injury, impaired renal gluconeogenesis could significantly participate in systemic metabolic disturbance and thus alter the prognosis. This review summarizes the biochemistry of gluconeogenesis, the current knowledge of kidney gluconeogenesis, its modifications in kidney disease and the clinical relevance of this fundamental biological process in human biology.

Responses to peripheral neuropeptide Y in avian adipose tissue are diet, depot, and time specific

The goal of this research was to determine the effect of dietary macronutrient composition on peripheral neuropeptide Y (NPY)-induced changes in adipose tissue dynamics in chicks. Chicks were fed one of three isocaloric diets from the day of hatch: high carbohydrate (HC), high fat (HF), or high protein (HP). On day 4 post-hatch, 0 (vehicle), 60, or 120 µg/kg BW of NPY was injected intraperitoneally, and subcutaneous, clavicular and abdominal adipose tissue samples were collected at 1 and 3 h post-injection. The effect of NPY was most pronounced in chicks fed the HF or HP diet. In the subcutaneous fat at 1 h post-injection, 60 µg/kg BW of NPY was associated with an increase in NPY receptor 2 (NPYR2) mRNA in chicks fed the HP diet and a decrease in 1-acylglycerol-3-phosphate O-acyltransferase 2 (AGPAT2) mRNA in chicks fed the HC diet. In response to 120 µg/kg BW of NPY, there was greater AGPAT2 mRNA in the clavicular fat of chicks that consumed the HP diet and less CCAAT/enhancer-binding protein alpha in the abdominal fat of chicks that were provided the HF diet. There were no gene expression changes in the abdominal fat at 3 h post-injection, whereas there were decreases in AGPAT2, adipose triglyceride lipase, fatty acid binding protein 4 and NPY mRNA in the clavicular fat of chicks fed the HP diet. Results demonstrate that diet affects exogenous NPY-dependent physiological effects in a time- and depot-dependent manner in chick adipose tissue.

The homeostatic role of neuropeptide Y in immune function and its impact on mood and behaviour

Neuropeptide Y (NPY), one of the most abundant peptides in the nervous system, exerts its effects via five receptor types, termed Y1, Y2, Y4, Y5 and Y6. NPY's pleiotropic functions comprise the regulation of brain activity, mood, stress coping, ingestion, digestion, metabolism, vascular and immune function. Nerve-derived NPY directly affects immune cells while NPY also acts as a paracrine and autocrine immune mediator, because immune cells themselves are capable of producing and releasing NPY. NPY is able to induce immune activation or suppression, depending on a myriad of factors such as the Y receptors activated and cell types involved. There is an intricate relationship between psychological stress, mood disorders and the immune system. While stress represents a risk factor for the development of mood disorders, it exhibits diverse actions on the immune system as well. Conversely, inflammation is regarded as an internal stressor and is increasingly recognized to contribute to the pathogenesis of mood and metabolic disorders. Intriguingly, the cerebral NPY system has been found to protect against distinct disturbances in response to immune challenge, attenuating the sickness response and preventing the development of depression. Thus, NPY plays an important homeostatic role in balancing disturbances of physiological systems caused by peripheral immune challenge. This implication is particularly evident in the brain in which NPY counteracts the negative impact of immune challenge on mood, emotional processing and stress resilience. NPY thus acts as a unique signalling molecule in the interaction of the immune system with the brain in health and disease.

Hypothalamus-adipose tissue crosstalk: neuropeptide Y and the regulation of energy metabolism

Neuropeptide Y (NPY) is an orexigenic neuropeptide that plays a role in regulating adiposity by promoting energy storage in white adipose tissue and inhibiting brown adipose tissue activation in mammals. This review describes mechanisms underlying NPY's effects on adipose tissue energy metabolism, with an emphasis on cellular proliferation, adipogenesis, lipid deposition, and lipolysis in white adipose tissue, and brown fat activation and thermogenesis. In general, NPY promotes adipocyte differentiation and lipid accumulation, leading to energy storage in adipose tissue, with effects mediated mainly through NPY receptor sub-types 1 and 2. This review highlights hypothalamus-sympathetic nervous system-adipose tissue innervation and adipose tissue-hypothalamus feedback loops as pathways underlying these effects. Potential sources of NPY that mediate adipose effects include the bloodstream, sympathetic nerve terminals that innervate the adipose tissue, as well as adipose tissue-derived cells. Understanding the role of central vs. peripherally-derived NPY in whole-body energy balance could shed light on mechanisms underlying the pathogenesis of obesity. This information may provide some insight into searching for alternative therapeutic strategies for the treatment of obesity and associated diseases.

Dysbalance in sympathetic neurotransmitter release and action in cirrhotic rats: impact of exogenous neuropeptide Y

BACKGROUND & AIMS

Splanchnic vasodilation is an essential disturbance in portal hypertension. Increased systemic sympathetic nerve activity is well known, but potential corresponding vascular desensitization is incompletely characterized. Release of splanchnic sympathetic neurotransmitters noradrenaline (NA) and co-transmitter neuropeptide Y (NPY) remains to be elucidated. Finally, the effects of exogenous NPY on these mechanisms are unexplored.

METHODS

Portal vein ligated cirrhotic, and control rats were used for in vitro perfusion of mesenteric arteries. Depletion of vascular pressure response was induced by repetitive electric sympathetic perivascular nerve stimulation (PNS) and performed in the absence and presence of exogenous NPY. Additionally, PNS-induced release of NA and NPY was measured.

RESULTS

Mesenteric PNS-induced pressure response was lower in portal hypertension. Depletion of the pressure response to PNS, representing the degree of desensitization, was enhanced in portal hypertension. NA release was elevated, whereas NPY release was attenuated in cirrhosis. Administration of exogenous NPY led to marked recovery from desensitization and vasoconstrictive improvement in cirrhotic rats, being associated with more pronounced decrease of NA release.

CONCLUSIONS

Pronounced depletion of splanchnic arterial pressure-response to repetitive sympathetic nerve stimulation in cirrhosis is partly attributable to altered NA release as well as to deficient NPY release. External NPY restores vascular contractility and attenuates pathologically elevated NA release in the portal hypertensive mesenteric vasculature, revealing post-, and prejunctional effects at the vascular smooth muscle motor endplate; therefore outlining encouraging therapeutic strategies.

Central functions of neuropeptide Y in mood and anxiety disorders

INTRODUCTION

Neuropeptide Y (NPY) is a highly conserved neuropeptide belonging to the pancreatic polypeptide family. Its potential role in the etiology and pathophysiology of mood and anxiety disorders has been extensively studied. NPY also has effects on feeding behavior, ethanol intake, sleep regulation, tissue growth and remodeling. Findings from animal studies have delineated the physiological and behavioral effects mediated by specific NPY receptor subtypes, of which Y1 and Y2 are the best understood.

AREAS COVERED

Physiological roles and alterations of the NPYergic system in anxiety disorders, depression, posttraumatic stress disorder (PTSD), alcohol dependence and epilepsy. For each disorder, studies in animal models and human investigations are outlined and discussed, focusing on behavior, neurophysiology, genetics and potential for novel treatment targets.

EXPERT OPINION

The wide implications of NPY in psychiatric disorders such as depression and PTSD make the NPYergic system a promising target for the development of novel therapeutic interventions. These include intranasal NPY administration, currently under study, and the development of agonists and antagonists targeting NPY receptors. Therefore, we are proposing that via this mode of administration, NPY might exert CNS therapeutic actions without untoward systemic effects. Future work will show if this is a feasible approach.

NPY and stress 30 years later: the peripheral view

Almost 30 years ago, neuropeptide Y (NPY) was discovered as a sympathetic co-transmitter and one of the most evolutionarily conserved peptides abundantly present all over the body. Soon afterward, NPY's multiple receptors were characterized and cloned, and the peptide's role in stress was first documented. NPY has proven to be pivotal for maintaining many stress responses. Most notably, NPY is known for activating long-lasting vasoconstriction in many vascular beds, including coronary arteries. More recently, NPY was found to play a role in stress-induced accretion of adipose tissue which many times can lead to detrimental metabolic changes. It is however due to its prominent actions in the brain, one of which is its powerful ability to stimulate appetite as well as its anxiolytic activities that NPY became a peptide of importance in neuroscience. In contrast, its actions in the rest of the body, including its role as a stress mediator, remained, surprisingly underappreciated and not well understood. Our research has focused on that other, "peripheral" side of NPY. In this review, we will discuss those actions of NPY on the cardiovascular system and metabolism, as they relate to adaptation to stress, and attempt to both distinguish NPY's effects from and integrate them with the effects of the classical stress mediators, glucocorticoids, and catecholamines. To limit the bias of someone (ZZ) who has viewed the world of stress through the eyes of NPY for over 20 years, fresh insight (DH) has been solicited to more objectively assess NPY's contributions to stress-related diseases and the body's ability to adapt to stress.

Renal lactate elimination is maintained during moderate exercise in humans

Reduced hepatic lactate elimination initiates blood lactate accumulation during incremental exercise. In this study, we wished to determine whether renal lactate elimination contributes to the initiation of blood lactate accumulation. The renal arterial-to-venous (a-v) lactate difference was determined in nine men during sodium lactate infusion to enhance the evaluation (0.5 mol x L(-1) at 16 ± 1 mL x min(-1); mean ± s) both at rest and during cycling exercise (heart rate 139 ± 5 beats x min(-1)). The renal release of erythropoietin was used to detect kidney tissue ischaemia. At rest, the a-v O(2) (CaO(2)-CvO(2)) and lactate concentration differences were 0.8 ± 0.2 and 0.02 ± 0.02 mmol x L(-1), respectively. During exercise, arterial lactate and CaO(2)-CvO(2) increased to 7.1 ± 1.1 and 2.6 ± 0.8 mmol x L(-1), respectively (P < 0.05), indicating a -70% reduction of renal blood flow with no significant change in the renal venous erythropoietin concentration (0.8 ± 1.4 U x L(-1)). The a-v lactate concentration difference increased to 0.5 ± 0.8 mmol x L(-1), indicating similar lactate elimination as at rest. In conclusion, a -70% reduction in renal blood flow does not provoke critical renal ischaemia, and renal lactate elimination is maintained. Thus, kidney lactate elimination is unlikely to contribute to the initial blood lactate accumulation during progressive exercise.

Intraportal administration of neuropeptide Y and hepatic glucose metabolism

We examined whether intraportal delivery of neuropeptide Y (NPY) affects glucose metabolism in 42-h-fasted conscious dogs using arteriovenous difference methodology. The experimental period was divided into three subperiods (P1, P2, and P3). During all subperiods, the dogs received infusions of somatostatin, intraportal insulin (threefold basal), intraportal glucagon (basal), and peripheral intravenous glucose to increase the hepatic glucose load twofold basal. Following P1, in the NPY group (n = 7), NPY was infused intraportally at 0.2 and 5.1 pmol.kg(-1).min(-1) during P2 and P3, respectively. The control group (n = 7) received intraportal saline infusion without NPY. There were no significant changes in hepatic blood flow in NPY vs. control. The lower infusion rate of NPY (P2) did not enhance net hepatic glucose uptake. During P3, the increment in net hepatic glucose uptake (compared with P1) was 4 +/- 1 and 10 +/- 2 micromol.kg(-1).min(-1) in control and NPY, respectively (P < 0.05). The increment in net hepatic fractional glucose extraction during P3 was 0.015 +/- 0.005 and 0.039 +/- 0.008 in control and NPY, respectively (P < 0.05). Net hepatic carbon retention was enhanced in NPY vs. control (22 +/- 2 vs. 14 +/- 2 micromol.kg(-1).min(-1), P < 0.05). There were no significant differences between groups in the total glucose infusion rate. Thus, intraportal NPY stimulates net hepatic glucose uptake without significantly altering whole body glucose disposal in dogs.

Modulator role of neuropeptide Y in human vascular sympathetic neuroeffector junctions

Reverse transcription polymerase chain reaction (RT-PCR) studies identified the mRNA coding for the Y1 and Y2 receptors in human mammary artery/vein and saphenous vein biopsies. Y1 receptors are expressed in vascular smooth muscles and potentiate the contractile action of sympathetic co-transmitters, adenosine triphosphate (ATP) and noradrenaline (NA); BIBP 3226, a competitive Y1 receptor antagonist, blocked the neuropeptide Y (NPY)-induced modulation. The Y2 receptor is expressed in sympathetic nerves terminals and modulates the pool of sympathetic co-transmitters released at the neuroeffector junction. NPY plays a dual role as a modulator of sympathetic co-transmission; it facilitates vascular smooth muscle reactivity and modulates the presynaptic release of ATP and NA. Sympathetic reflexes regulate human vascular resistance, where NPY plays a modulator role of paramount importance following increased sympathetic discharges, such as stress and vascular disease.

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.

Neuropeptide Y is released from human mammary and radial vascular biopsies and is a functional modulator of sympathetic cotransmission

The role of neuropeptide Y (NPY) as a modulator of the vasomotor responses mediated by sympathetic cotransmitters was examined by electrically evoking its release from the perivascular nerve terminals of second- to third-order human blood vessel biopsies and by studying the peptide-induced potentiation of the vasomotor responses evoked by exogenous adenosine 5' triphosphate (ATP) and noradrenaline (NA). Electrical depolarization of nerve terminals in mammary vessels and radial artery biopsies elicited a rise in superfusate immunoreactive NPY (ir-NPY), which was chromatographically identical to a standard of human NPY (hNPY); a second peak was identified as oxidized hNPY. The amount released corresponds to 4-6% of the total NPY content in these vessels. Tissue extracts also revealed two peaks; hNPY accounted for 68-85% of the ir-NPY, while oxidized hNPY corresponded to 7-15%. The release process depended on extracellular calcium and on the frequency and duration of the electrical stimuli; guanethidine blocked the release, confirming the peptide's sympathetic origin. Assessment of the functional activity of the oxidized product demonstrated that while it did not change basal tension, the NA-evoked contractions were potentiated to the same extent as with native hNPY. Moreover, NPY potentiated both the vasomotor action of ATP or NA alone and the vasoconstriction elicited by the simultaneous application of both cotransmitters. RT-PCR detected the mRNA coding for the NPY Y(1) receptor. In summary, the release of hNPY or its oxidized species, elicited by nerve terminal depolarization, coupled to the potentiation of the sympathetic cotransmitter vasomotor responses, highlights the modulator role of NPY in both arteries and veins, strongly suggesting its involvement in human vascular sympathetic reflexes.

Release and functional role of neuropeptide Y as a sympathetic modulator in human saphenous vein biopsies

Transmural electrical stimulation of the sympathetic nerve endings of human saphenous vein biopsies released two forms of NPY identified chromatographically as native and oxidized peptide. The release process is dependent on extracellular calcium, the frequency, and the duration of the stimuli. While guanethidine reduced the overflow of ir-NPY, phenoxybenzamine did not augment NPY release, but increased that of noradrenaline. Oxidized NPY, like native NPY, potentiated the noradrenaline and adenosine 5'-triphospahate-induced vasoconstriction, an effect blocked by BIBP 3226 and consonant with the RT-PCR detection of the mRNA encoding the NPY Y1 receptor. These results highlight the functional role of NPY in human vascular sympathetic reflexes.

Bench-to-bedside review: glucose production from the kidney

Data obtained from net organ balance studies of glucose production lead to the classic view according to which glucose homeostasis is mainly ensured by the liver, and renal glucose production only plays a significant role during acidosis and prolonged starvation. Renal glucose release and uptake, as well as the participation of gluconeogenic substrates in renal gluconeogenesis, were recently re-evaluated using systemic and renal arteriovenous balance of substrates in combination with deuterated glucose dilution. Data obtained using these methods lead one to reconsider the magnitude of renal glucose production as well as its role in various physiological and pathological circumstances. These findings now conduce one to consider that renal gluconeogenesis substantially participates in postabsorptive glucose production, and that its role in glucose homeostasis is of first importance.

Role of the kidney in hyperglycemia in type 2 diabetes

Overproduction of glucose is the major factor responsible for fasting hyperglycemia in type 2 diabetes. Formerly, this had been considered to be solely due to excessive hepatic glucose production because the human kidney was not regarded as an important source of glucose except during acidosis and after prolonged fasting. However, data accumulated over the last 60 years in animal and in vitro studies have provided considerable evidence that the kidney plays an important role in glucose homeostasis in conditions other than acidosis and prolonged fasting. This article summarizes early work in animals and humans, discusses methodologic issues in assessing renal glucose release in vivo, and provides evidence from recent human studies that the kidney substantially contributes to glucose overproduction in type 2 diabetes.

Neurohormonal activation in heart failure after acute myocardial infarction treated with beta-receptor antagonists

BACKGROUND

Few studies have described how neurohormonal activation is influenced by treatment with beta-receptor antagonists in patients with heart failure after acute myocardial infarction. The aims were to describe neurohormonal activity in relation to other variables and to investigate treatment effects of a beta(1) receptor-antagonist compared to a partial beta(1) receptor-agonist.

METHODS

Double-blind, randomized comparison of metoprolol 50-100 mg b.i.d. (n=74), and xamoterol 100-200 mg b.i.d (n=67). Catecholamines, neuropeptide Y-like immunoreactivity (NPY-LI), renin activity, and N-terminal pro-atrial natriuretic factor (N-ANF) were measured in venous plasma before discharge and after 3 months. Clinical and echocardiographic variables were assessed.

RESULTS

N-ANF showed the closest correlations to clinical and echocardiographic measures of heart failure severity, e.g. NYHA functional class, furosemide dose, exercise tolerance, systolic and diastolic function. Plasma norepinephrine, dopamine and renin activity decreased after 3 months on both treatments, in contrast to a small increase in NPY-LI which was greater (by 3.9 pmol/l, 95% CI 1.2-6.6) in the metoprolol group. N-ANF increased on metoprolol, and decreased on xamoterol (difference: 408 pmol/l, 95% CI 209-607). Increase above median of NPY-LI (>25.2 pmol/l, odds ratio 2.8, P=0.0050) and N-ANF (>1043 pmol/l, odds ratio 2.8, P=0.0055) were related to long term (mean follow-up 6.8 years) cardiovascular mortality.

CONCLUSIONS

Decreased neurohormonal activity, reflecting both the sympathetic nervous system and the renin-angiotensin system, was found 3 months after an acute myocardial infarction with heart failure treated with beta-receptor antagonists. The small increase in NPY-LI may suggest increased sympathetic activity or reduced clearance from plasma. The observed changes of N-ANF may be explained by changes in cardiac preload, renal function, and differences in beta-receptor mediated inhibition of atrial release of N-ANF. NPY-LI, and N-ANF at discharge were related to long term cardiovascular mortality.

Role of neuropeptide Y in renal sympathetic vasoconstriction: studies in normal and congestive heart failure rats

Sympathetic nerve activity, including that in the kidney, is increased in heart failure with increased plasma concentrations of norepinephrine and the vasoconstrictor cotransmitter neuropeptide Y (NPY). We examined the contribution of NPY to sympathetically mediated alterations in kidney function in normal and heart failure rats. Heart failure rats were created by left coronary ligation and myocardial infarction. In anesthetized normal rats, the NPY Y(1) receptor antagonist, H 409/22, at two doses, had no effect on heart rate, arterial pressure, or renal hemodynamic and excretory function. In conscious severe heart failure rats, high-dose H 409/22 decreased mean arterial pressure by 8 +/- 2 mm Hg but had no effect in normal and mild heart failure rats. During graded frequency renal sympathetic nerve stimulation (0 to 10 Hz), high-dose H 409/22 attenuated the decreases in renal blood flow only at 10 Hz (-36% +/- 5%, P <.05) in normal rats but did so at both 4 (-29% +/- 4%, P <.05) and 10 Hz (-33% +/- 5%, P <.05) in heart failure rats. The glomerular filtration rate, urinary flow rate, and sodium excretion responses to renal sympathetic nerve stimulation were not affected by high-dose H 409/22 in either normal or heart failure rats. NPY does not participate in the regulation of kidney function and arterial pressure in normal conscious or anesthetized rats. When sympathetic nervous system activity is increased, as in heart failure and intense renal sympathetic nerve stimulation, respectively, a small contribution of NPY to maintenance of arterial pressure and to sympathetic renal vasoconstrictor responses may be identified.

Inter-relationships between renal metabolism (both in physiology and renal dysfunction) and the liver

Recently, evaluation of organ-specific glucose release showed that renal glucose release is of the same order of magnitude as splanchnic glucose release during the postabsorptive period. Moreover, renal glucose release appeared to be more sensitive to hormone action than did hepatic glucose release, and appeared to have a pre-eminent role during the adaptation to various physiological and pathological conditions. The kidney is now recognized as playing a key role in interorgan glucose metabolism, and particularly in the Cori cycle and glutamine-glucose cycle. During chronic renal failure the suppression of renal glucose release, together with impaired hormone action, decreased glycogen storage and abnormal liver gluconeogenesis, are responsible for an increased risk for hypoglycaemia.

Early neurohormonal effects of trandolapril in patients with left ventricular dysfunction and a recent acute myocardial infarction: a double-blind, randomized, placebo-controlled multicentre study

Angiotensin-converting enzyme inhibitors improve long-term survival in patients with left ventricular dysfunction after a myocardial infarction, but their mechanism of action is not entirely clear. The neurohormonal effects may be important in this respect, as well as an early hemodynamic unloading induced by these drugs. The primary objective was to assess the effect of trandolapril on plasma levels of atrial natriuretic peptide. A secondary objective was to assess the effects of trandolapril on selected neurohormones, vasoactive peptides and enzymes, which may be important in the development of left ventricular remodeling and heart failure following an acute myocardial infarction. A total of 119 patients with an acute myocardial infarction and a wall motion index < or =1.2 (16-segment echocardiographic model) were randomized to double blind treatment with trandolapril or placebo within 3-7 days after the onset of infarction. Blind treatment was discontinued 21 days after the index infarction. Venous blood samples were collected at rest, before randomization and on the day after treatment was discontinued. At the end of the study, there were no differences in plasma levels of atrial natriuretic peptide between the two treatment groups. Angiotensin-converting enzyme activity was suppressed and plasma renin activity was higher in the trandolapril group. No differences in plasma levels of N-terminal pro-atrial natriuretic peptide, brain natriuretic peptide, aldosterone, noradrenaline, adrenaline, vasopressin, big endothelin-1 and neuropeptide Y were found between the two treatment groups. There were positive correlations between several markers of neurohormonal activation at baseline and variables expressing left ventricular dysfunction and clinical heart failure. Neurohormonal activation is related to left ventricular dysfunction. The effects of 2-3 weeks of angiotensin-converting enzyme inhibition on neurohormonal activation does not predict the already established beneficial long-term effects after myocardial infarction. Thus, early modulation of circulatory neurohormone levels may not be a major mechanism for the efficacy of angiotensin-converting enzyme inhibitors in these patients. Selected plasma hormone markers may still be used to identify patients who might get the greatest benefit from treatment.

Neuropeptide Y Y1 receptor mediated mesenteric vasoconstriction in the pig in vivo

The object of the present study was to investigate the effects of the sympathetic cotransmitter neuropeptide Y (NPY), and the closely related gut hormone peptide YY (PYY), on splanchnic blood flow regulation in the anaesthetized pig in vivo. Systemic injections of NPY, PYY and the NPY Y(1) receptor agonist [Leu(31)Pro(34)]NPY (470 pmol kg(-1) each) evoked pressor and mesenteric vasoconstrictor responses that were largely abolished by the selective NPY Y(1) receptor antagonist H 409/22 (60 nmol kg(-1) min(-1)). In contrast, the NPY Y(2) receptor agonist N-acetyl[Leu(28)Leu(31)]NPY(24-36) (1.1 nmol kg(-1)), a dose of which potently evoked splenic NPY Y(2) receptor mediated (not affected by H 409/22) vasoconstriction, did not evoke any mesenteric vascular response. Mesenteric vascular responses to angiotensin II (10 pmol kg(-1)), alpha,beta-methylene ATP (10 nmol kg(-1)) and the alpha(1)-adrenoceptor agonist phenylephrine (15 nmol kg(-1)), were not inhibited by H 409/22. It is concluded that NPY and PYY evokes porcine mesenteric vasoconstriction mediated by the NPY Y(1) receptor subtype, as demonstrated by selective and specific inhibition exerted by the NPY Y(1) receptor antagonist H 409/22, in vivo.

Molecular characterization of the ligand-receptor interaction of the neuropeptide Y family

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) belong to the NPY hormone family and activate a class of receptors called the Y-receptors, and also belong to the large superfamily of the G-protein coupled receptors. Structure-affinity and structure-activity relationship studies of peptide analogs, combined with studies based on site-directed mutagenesis and anti-receptor antibodies, have given insight into the individual characterization of each receptor subtype relative to its interaction with the ligand, as well as to its biological function. A number of selective antagonists at the Y1-receptor are available whose structures resemble that of the C-terminus of NPY. Some of these compounds, like BIBP3226, BIBO3304 and GW1229, have recently been used for in vivo investigations of the NPY-induced increase in food intake. Y2-receptor selective agonists are the analog cyclo-(28/32)-Ac-[Lys28-Glu32]-(25-36)-pNPY and the TASP molecule containing two units of the NPY segment 21-36. Now the first antagonist with nanomolar affinity for the Y2-receptor is also known, BIIE0246. So far, the native peptide PP has been shown to be the most potent ligand at the Y4-receptor. However, by the design of PP/NPY chimera, some analogs have been found that bind not only to the Y4-, but also to the Y5-receptor with subnanomolar affinities, and are as potent as NPY at the Y1-receptor. For the characterization of the Y5-receptor in vitro and in vivo, a new class of highly selective agonists is now available. This consists of analogs of NPY and of PP/NPY chimera which all contain the motif Ala31-Aib32. This motif has been shown to induce a 3(10)-helical turn in the region 28-31 of NPY and is suggested to be the key motif for high Y5-receptor selectivity. The results of feeding experiments in rats treated with the first highly specific Y5-receptor agonists support the hypothesis that this receptor plays a role in the NPY-induced stimulation of food intake. In conclusion, the selective compounds for the different Y receptor subtypes known so far are promising tools for a better understanding of the physiological properties of the hormones of the NPY family and related receptors.

Aetiology of running-related gastrointestinal dysfunction. How far is the finishing line?

30 to 65% of long distance runners experience gastrointestinal (GI) symptoms related to exercise. Several hypotheses have been postulated; however, the aetiology and pathophysiology are far from clear. The mechanical effect of running on the viscera must be involved in the development of GI symptoms in this sport. Reduction of splanchnic blood flow due to visceral vasoconstriction is another widely supported theory; nevertheless, it does not explain many of the clinical findings. Examination of the GI tract during exercise is a difficult task, and measurements of both orocaecal and whole-gut transit time have shown equivocal results. GI hormones, and especially prostaglandins, may be of crucial importance for the production of symptoms. Intestinal absorption, secretion and permeability may also be altered during exercise, provoking intestinal dysfunction. Factors such as stress, diet, dehydration, infections and other factors need to be analysed in order to present a global view of the hypotheses regarding the aetiology of this common and often overlooked problem.

[The human kidney as an important producer of glucose]

BACKGROUND

According to current textbook knowledge the liver is the exclusive site of glucose production in postabsorptive humans. Although many animal and in-vitro data have documented that the kidney is capable of gluconeogenesis, production of glucose by the human kidney has been regarded as negligible to date. This traditional perception is based on methodologically inadequate net balance studies, which other than after a prolonged fast or during metabolic acidosis showed no significant net renal glucose release.

STUDIES

Recent tracer studies, however, showing a renal glucose production accounting for 25% of systemic glucose production, have refuted this view. glucose production by the human kidney is stimulated by epinephrine and inhibited by insulin. Glucagon stimulates hepatic but not renal glucose production. The most important renal gluconeogenic precursors are lactate, glutamine and glycerol. The implications of these recent findings on the understanding of the physiology and pathophysiology of human glucose metabolism are discussed.

CONCLUSION

Magnitude and regulation of renal glucose production have important consequences for the intermediary metabolism, counterregulation of hypoglycemia, glucose metabolism of uremia and the pathophysiology of type I and type II diabetes.

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.

Exercise-induced changes in neuropeptide Y, noradrenaline and endothelin-1 levels in young people with type I diabetes

In search of early signs of autonomic and vascular dysfunction in diabetic subjects, six young men with type I diabetes and six healthy subjects were investigated regarding arterial levels of noradrenaline (NA), neuropeptide Y- (NPY) and endothelin-1-(ET-1) like immunoreactivity (Li) during and after 1 h of exercise at 70% of peak oxygen uptake. Basal NA, NPY-Li and ET-1-Li levels did not differ between groups. NA and NPY-Li rose during exercise in diabetic subjects to only 60% of the control values (P < 0.05, interaction group x time P < 0.001). Disappearance rates for NA and NPY-Li did not differ between groups. Plasma ET-1-Li did not differ between groups during exercise. Values returned to basal levels within 5 min in the diabetic but not in the control group. In conclusion, diabetic subjects show lower NPY-Li and NA levels than control subjects during exercise but similar disappearance rates after exercise, indicating lower releases. Furthermore, plasma ET-1 levels did not differ between groups during exercise.

Somatostatin and vasoactive intestinal peptide (VIP) in neuroblastoma and ganglioneuroma: chromatographic characterisation and release during surgery

Neuroblastomas and ganglioneuromas frequently produce somatostatin (SOM) and vasoactive intestinal peptide (VIP), and elevated concentrations in tumour tissue are associated with favourable outcome. Both somatostatin and VIP have been shown to have an autocrine effect on tumour growth and differentiation in vitro, and VIP may cause clinical symptoms when released systemically. Using gel-permeation chromatography and specific radioimmunoassays, we further characterised somatostatin-like immunoreactivity (SOM-LI) and VIP-like immunoreactivity (VIP-LI) in neuroblastoma and ganglioneuroma tumour tissue. The major part of SOM-LI and VIP-LI in both neuroblastoma and ganglioneuroma represents the biologically active forms SOM-28, SOM-14 and VIP-2, respectively. 21 children with neuroblastoma and ganglioneuroma were monitored with serial plasma samples during surgery. In 8 children with measurable concentrations of SOM-LI, all showed increased concentrations during tumour manipulation (P = 0.004) that subsequently decreased below preoperative levels in all but one case (P = 0.06). The only child presenting with diarrhoea showed the highest preoperative plasma VIP-LI in the study (54 pmol/l). 2 children with increased concentrations of VIP-LI preoperatively showed a rapid decrease after surgical tumour removal. These findings indicate a systemic release from the tumours. It is concluded that plasma and tumour tissue from children with neuroblastoma and ganglioneuroma contain biologically active molecular forms of somatostatin and vasoactive intestinal peptide. These peptides may bear significance both for specific symptoms in certain patients as well as influencing tumour growth and differentiation in vivo.

Vasoconstrictive action of neuropeptide Y in bone. The porcine tibia perfused in vivo

The hemodynamic effects of neuropeptide Y (NPY) and norepinephrine (NE) in bone were studied by infusion into the nutrient artery of an in vivo and in situ perfused tibia in 19 pigs. NPY and NE caused elevation of the perfusion pressure and decline in intraosseous pressure, which was evidence of intraosseous vasoconstriction. The study suggests that NPY, along with NE, acts as a sympathetic neurotransmitter in the control of vascular tone in bone.

Inhibitory effects of neuropeptide Y on splanchnic glycogenolysis and renin release in humans

Neuropeptide Y (NPY) is stored in sympathetic nerves and NPY levels increase several times during exercise. NPY administration during prolonged exercise causes reduced splanchnic glucose production. To elucidate the effects of NPY on adrenaline (Adr)-stimulated splanchnic glycogenolysis these substances were infused to seven healthy subjects in the post-absorptive state. Blood samples were drawn from an arterial and a central hepatic vein catheter for determination of splanchnic blood flow, exchanges of metabolites and arterial levels of NPY, catecholamines, insulin, glucagon and renin in the basal state and during 20 min Adr infusion (0.1-0.3 nmol kg-1 min-1). After basal values were reached a 60 min NPY infusion was initiated. At 40 min of NPY infusion the Adr infusion was repeated. Adr alone increased splanchnic blood flow (41%, P < 0.01), arterial glucose concentration (29%, P < 0.001) and splanchnic glucose production (102%, P < 0.01). During the NPY infusion both splanchnic blood flow and arterial glucose fell (P < 0.05). Although the combined NPY and Adr infusion caused the same proportional increases in splanchnic blood flow, arterial glucose and splanchnic glucose production as with Adr alone the absolute values were lower (all P < 0.05). Arterial insulin as well as Adr and noradrenaline increased with the combined NPY-and Adr infusion as with Adr alone. Arterial plasma renin activity was 12% lower with the combined NPY and Adr-infusion compared to Adr infusion alone. These results indicate further an inhibitory effect of NPY on splanchnic glycogenolysis and suggest that NPY inhibits Adr-stimulated renin release.