Galanin/alpha2-receptor interactions in central cardiovascular control

Short N-terminal galanin fragments are occurring naturally in vivo

The galanin family currently consists of four peptides, namely galanin, galanin-message associated peptide, galanin-like peptide and alarin. Unlike galanin that signals through three different G protein-coupled receptors; GAL₁, GAL₂, and GAL₃, binding at its N-terminal end, the cognate receptors for other members of the galanin family are currently unknown. Research using short N-terminal galanin fragments generated either by enzymatic cleavage or solid-phase synthesis has revealed differences in their receptor binding properties exerting numerous biological effects distinct from galanin(1-29) itself. Our studies on tissue extracts derived from rat small intestine and bovine gut using chromatographic techniques and sensitive galanin(1-16)-specific radioimmunoassay revealed the presence of immunoreactive compounds reacting with antiserum against galanin(1-16) distributed in distinct elution volumes. These results suggested a possible presence of short N-terminal galanin fragments also in vivo. Moreover, employing immunoaffinity chromatography and reverse-phase high performance liquid chromatography (HPLC) followed by mass spectrometry allowed specific enrichment of these immunoreactive compounds from rat tissues and identification of their molecular structure. Indeed, our study revealed presence of several distinct short N-terminal galanin sequences in rat tissue. To prove their receptor binding, four of the identified sequences were synthetized, namely, galanin(1-13), galanin(1-16), galanin(1-20), galanin(6-20), and tested on coronal rat brain sections competing with ¹²⁵I-labeled galanin(1-29). Our autoradiographs confirmed that galanin(1-13), galanin(1-16), and galanin(1-20) comprehensively displaced ¹²⁵I-galanin(1-29) but galanin(6-20) did not. Here we show, for the first time, that short N-terminal galanin fragments occur naturally in rat tissues and that similar or identical galanin sequences can be present also in tissues of other species.

BIOLOGICAL SIGNIFICANCE

This study is first to provide an evidence of the presence of short N-terminal galanin fragments in vivo in a biological system and provides further foundations for the previous studies using synthetized short N-terminal galanin fragments.

Low levels of plasma galanin in obese subjects with hypertension

BACKGROUND

Obesity is strongly linked to increased blood pressure, which increases the risk of cardiovascular diseases. To our knowledge, little literature reported the information about galanin levels in obese individuals with hypertension. Therefore, the aim of this study was to investigate the possible involvement of galanin in the pathogenesis of obese subjects with hypertension.

METHODS

We measured body mass index and blood pressure of 38 obese patients with hypertension, 44 obese controls with normal blood pressure and 44 lean controls with normal blood pressure. Blood samples from all cases were collected at 8:00 a.m. after an overnight fast to determine the fasting plasma concentration of galanin, glucose, insulin, triglyceride, total cholesterol, high- and low-density lipoprotein cholesterol.

RESULTS

We found that plasma galanin levels were significantly decreased in obese patients with hypertension compared with the obese control group, whereas the galanin levels were significantly increased in obese controls compared with lean controls. Furthermore, in both obese groups the galanin levels were negatively correlative to diastolic blood pressure and positively correlative to insulin and triglyceride levels, but not to heart rate.

CONCLUSIONS

Low galanin levels were one of characters of obese patients with high blood pressure, and this levels may be taken as a novel biomarker to predict the development of high blood pressure in obese patients.

The role of food intake regulating peptides in cardiovascular regulation

Obesity is a risk factor that worsens cardiovascular events leading to higher morbidity and mortality. However, the exact mechanisms of relation between obesity and cardiovascular events are unclear. Nevertheless, it has been demonstrated that pharmacological therapy for obesity has great potential to improve some cardiovascular problems. Therefore, it is important to determine the common mechanisms regulating both food intake and blood pressure. Several hormones produced by peripheral tissues work together with neuropeptides involved in the regulation of both food intake and blood pressure. Anorexigenic (food intake lowering) hormones such as leptin, glucagon-like peptide-1 and cholecystokinin cooperate with α-melanocyte-stimulating hormone, cocaine- and amphetamine-regulated peptide as well as prolactin-releasing peptide. Curiously their collective actions result in increased sympathetic activity, especially in the kidney, which could be one of the factors responsible for the blood pressure increases seen in obesity. On the other hand, orexigenic (food intake enhancing) peptides, especially ghrelin released from the stomach and acting in the brain, cooperates with orexins, neuropeptide Y, melanin-concentrating hormone and galanin, which leads to decreased sympathetic activity and blood pressure. This paradox should be intensively studied in the future. Moreover, it is important to know that the hypothalamus together with the brainstem seem to be major structures in the regulation of food intake and blood pressure. Thus, the above mentioned regions might be essential brain components in the transmission of peripheral signals to the central effects. In this short review, we summarize the current information on cardiovascular effects of food intake regulating peptides.

Circulating galanin and IL-6 concentrations in gestational diabetes mellitus

OBJECTIVE

The aim of this study is to compare galanin and IL-6 levels in pregnant women with gestational diabetes mellitus (GDM) and normal glucose tolerance (NGT). Also association of insulin resistance markers, galanin and IL-6 was investigated.

MATERIALS AND METHODS

The study registered 30 pregnant women with GDM and 30 pregnant women with NGT. Fasting venous blood samples were collected from all patients. Galanin and IL-6 levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

Galanin and IL-6 levels were found higher in pregnant women with GDM (p < 0.001). A significant positive correlation was determined between galanin concentrations and glucose (r = 0.240, p = 0.065), insulin (r = 0.681, p < 0.001), HbA1c (r = -0.644, p < 0.001), IL-6 (r = 0.783, p < 0.05) and oral glucose challenge test results (r = 0.745, p < 0.001) in pregnant women included in study, whereas no significant association was determined between galanin and gestational age (r = 0.058, p = 0.662), body mass index (r = -0.019, p = 0.886).

CONCLUSION

Galanin and IL-6 were found to be significantly associated with insulin resistance markers in GDM, thus may play important roles in regulation of glucose hemostasis.

Galanin peptide family as a modulating target for contribution to metabolic syndrome

Metabolic syndrome (MetS) is defined as abdominal central obesity, atherogenic dyslipidemia, insulin resistance, glucose intolerance and hypertension. The rapid increasing prevalence of MetS and the consequent diseases, such as type 2 diabetes mellitus and cardiovascular disorder, are becoming a global epidemic health problem. Despite considerable research into the etiology of this complex disease, the precise mechanism underlying MetS and the association of this complex disease with the development of type 2 diabetes mellitus and increased cardiovascular disease remains elusive. Therefore, researchers continue to actively search for new MetS treatments. Recent animal studies have indicated that the galanin peptide family of peptides may increase food intake, glucose intolerance, fat preference and the risk for obesity and dyslipidemia while decreasing insulin resistance and blood pressure, which diminishes the probability of type 2 diabetes mellitus and hypertension. To date, however, few papers have summarized the role of the galanin peptide family in modulating MetS. Through a summary of available papers and our recent studies, this study reviews the updated evidences of the effect that the galanin peptide family has on the clustering of MetS components, including obesity, dyslipidemia, insulin resistance and hypertension. This line of research will further deepen our understanding of the relationship between the galanin peptide family and the mechanisms underlying MetS, which will help develop new therapeutic strategies for this complex disease.

The role of adrenomedullin and galanin in recurrent vasovagal syncope: a case control study

AIMS

Orthostatic stimuli are known to elicit changes in vasoactive peptide levels. The hypothesis of no difference in adrenomedullin and/or galanin levels in patients with recurrent vasovagal syncope and healthy controls was tested in a passive 35-min head-up tilt test (HUTT).

METHODS

Twenty eight persons (14 patients and 14 healthy controls) were tested in a 35-min/60° head-up tilt test with telemetry monitoring. Three blood samples were evaluated for each person during the HUTT. Plasma levels of adrenomedullin and galanin were analysed by the Kruskal-Wallis test for all sampling periods. Vagal influence was indirectly assessed by the break index.

RESULTS

There were no significant differences between groups in median values for either adrenomedullin or galanin plasma levels (all 6 p-values were greater than 0.4). For adrenomedullin, no significant difference between groups was found. For galanin, the rate of change between the 1st and 2nd measurement was significantly greater for patients (P=0.04), regardless of HUTT result but between the 2(nd) and 3(rd) measurement it was insignificant (P=0.36). In the group of positive cases, the break index increased significantly (P=0.02).

CONCLUSION

We confirmed that there is a different galanin secretion pattern during orthostatic provocation in patients with recurrent vasovagal syncope than healthy individuals. For adrenomedullin, no significant difference was found. A significant increment of the break index confirmed increased vagal influence in the subgroup of positive cases.

On the existence and function of galanin receptor heteromers in the central nervous system

Galanin receptor (GalR) subtypes 1-3 linked to central galanin neurons may form heteromers with each other and other types of G protein-coupled receptors in the central nervous system (CNS). These heteromers may be one molecular mechanism for galanin peptides and their N-terminal fragments (gal 1-15) to modulate the function of different types of glia-neuronal networks in the CNS, especially the emotional and the cardiovascular networks. GalR-5-HT1A heteromers likely exist with antagonistic GalR-5-HT1A receptor-receptor interactions in the ascending midbrain raphe 5-HT neuron systems and their target regions. They represent a novel target for antidepressant drugs. Evidence is given for the existence of GalR1-5-HT1A heteromers in cellular models with trans-inhibition of the protomer signaling. A GalR1-GalR2 heteromer is proposed to be a galanin N-terminal fragment preferring receptor (1-15) in the CNS. Furthermore, a GalR1-GalR2-5-HT1A heterotrimer is postulated to explain why only galanin (1-15) but not galanin (1-29) can antagonistically modulate the 5-HT1A receptors in the dorsal hippocampus rich in gal fragment binding sites. The results underline a putative role of different types of GalR-5-HT1A heteroreceptor complexes in depression. GalR antagonists may also have therapeutic actions in depression by blocking the antagonistic GalR-NPYY1 receptor interactions in putative GalR-NPYY1 receptor heteromers in the CNS resulting in increases in NPYY1 transmission and antidepressant effects. In contrast the galanin fragment receptor (a postulated GalR1-GalR2 heteromer) appears to be linked to the NPYY2 receptor enhancing the affinity of the NPYY2 binding sites in a putative GalR1-GalR2-NPYY2 heterotrimer. Finally, putative GalR-α2-adrenoreceptor heteromers with antagonistic receptor-receptor interactions may be a widespread mechanism in the CNS for integration of galanin and noradrenaline signals also of likely relevance for depression.

Neurochemical modulation of central cardiovascular control: the integrative role of galanin

Galanin (GAL) is a peptide involved in multiple functions, including central cardiovascular control. In this review, the role of GAL and its fragments in the modulation of cardiovascular neuronal networks in the nucleus of the solitary tract is presented, including its interaction with the classical neurotransmitters and other neuropeptides involved in cardiovascular responses in this nucleus. First, we describe the cardiovascular responses of GAL and the pathway involved in these responses. Then we summarize findings obtained in our laboratory on how GAL, through its receptors, interacts with two other neuropeptides--Neuropeptide Y and Angiotensin II and their receptors--as they have particularly conspicuous cardiovascular effects. All these results strengthen the role of GAL in central cardiovascular control and indicate the existence of interactions among GAL receptor subtypes and alpha2-adrenergic receptors, AT1, and Y1 receptor subtypes. These interactions are crucial for understanding the integrative mechanisms responsible for the organization of the cardiovascular responses from the NTS.

Hypotensive and antiaggregative effects of eugenosedin-B with serotonin and alpha/beta-adrenoceptor antagonistic activities in rats and human platelets

Eugenosedin-B is able to block serotonin (5-HT) and alpha/beta receptors and to inhibit platelet aggregation. In Wistar rats, intravenous injections of eugenosedin-B (2.4, 7.2, 12 micromoL/kg) caused a dose-dependent decrease in blood pressure and heart rate. In contrast, intracisternal injection of eugenosedin-B (0.3, 0.03 micromoL) and an alpha2-antagonist yohimbine (0.03 micromoL) increased blood pressure and heart rate. Eugenosedin-B and yohimbine prevented hypotension induced by intracisternal injection of an alpha2-agonist clonidine (38 pmol). In in vitro experiments, eugenosedin-B (10, 10, 10 M) competitively antagonized norepinephrine-, clonidine-, and 5-HT (10 to 10 M)-induced vasocontractions in isolated rat aorta. It also competitively antagonized the isoproterenol (10 to 10 M)-induced positive inotropic effects in isolated rat atrium. These findings clearly suggest that eugenosedin-B possesses alpha1, alpha2, beta1, and 5-HT2A receptor blocking activities. In isolated rabbit ear artery sensitized with 16 mM K, eugenosedin-B antagonized 5-nonyloxytryptamine- and 5-HT-induced vasocontractions, indicating it also blocked 5-HT1B and 5-HT2A receptors. In radioligand-binding experiments, eugenosedin-B had significant binding affinities on alpha1, alpha2, beta1, 5-HT1B, and 5-HT2A receptors. In human platelets, eugenosedin-B inhibited epinephrine and 5-HT-induced aggregations. It also had competitive binding effects in human platelet with [H]yohimbine (alpha2), [H]ketanserin (5-HT2A). We conclude that hypotensive and vasorelaxant effects of eugenosedin-B can be attributed to its multiple actions on the blockade of 5-HT1B, 5-HT2A, alpha1/2 and beta1 receptors, and its ability to reduce platelet aggregation attributed to its blockade of alpha2 and 5-HT2A receptors.

Region specific galanin receptor/neuropeptide Y Y1 receptor interactions in the tel- and diencephalon of the rat. Relevance for food consumption

The aim of this work was to determine the interactions between NPY and GAL receptor (GALR) subtypes in the hypothalamus and the amygdala using quantitative receptor autoradiography to analyze the binding characteristics of NPY-Y1 and Y2 receptor subtypes in the presence and absence of GAL. Food intake in satiated animals was evaluated after intraventricular co-injections of GAL and NPY-Y1 or Y2 agonists. The expression of c-Fos IR in both regions was also investigated. GAL decreases NPY-Y1 agonist binding in the arcuate nucleus by about 15% (p<0.01), but increases NPY-Y1 agonist binding in amygdala (18%) (p<0.01). These effects were blocked with the GAL antagonist M35. Y2-agonist binding was not modified by GAL. GAL blocked the food intake induced by the Y1 agonist (p<0.01). Co-injections of Y1 agonist and GAL also reduced the c-Fos expression induced by the Y1 agonist in the arcuate nucleus and the dorsomedial hypothalamic nucleus but increased c-Fos expression in amygdala. These results indicate the existence of antagonistic interactions between GALR and NPY-Y1 receptors in the hypothalamus and their functional relevance for food intake. In contrast, a facilitatory interaction between GALR and Y1 receptors exists in the amygdala which may be of relevance for fear related behaviour.

Receptor–receptor interactions in central cardiovascular regulation. Focus on neuropeptide/α2-adrenoreceptor interactions in the nucleus tractus solitarius

The nucleus tractus solitarii (NTS) is a key nucleus in central cardiovascular control. In this mechanism it is well known the role of the alpha(2)-adrenoreceptors for the modulation of the autonomic pathways. Moreover a number of neuropeptides described in the NTS, including Neuropeptide Y (NPY), Galanin (GAL) and Angiotensin II (Ang II), have different roles in regulating the cardiovascular function within this nucleus. We show in this review several data which help to understand how these neuropeptides (NPY, GAL and Ang II) could modulate the cardiovascular responses mediated through alpha(2)-adrenoreceptors in the NTS. Also we show for the first time the interactions between neuropeptides in the brain, specifically the interactions between NPY, GAL, and Ang II, and its functional relevance for central cardiovascular regulation. These data strength the role of neuropeptides on central autonomic control and provide some evidences to understand the neurochemical mechanisms involved in the cardiovascular responses from the NTS.

Galanin-neuropeptide Y (NPY) interactions in central cardiovascular control: involvement of the NPY Y1receptor subtype

The interactions between neuropeptide Y (NPY), specifically through NPY Y(1) and Y(2) receptor subtypes, and galanin [GAL(1-29)] have been analysed at the cardiovascular level. The cardiovascular effects of intracisternal coinjections of GAL(1-29) with NPY or NPY Y(1) or Y(2) agonists, as well as quantitative receptor autoradiography of the binding characteristics of NPY Y(1) and Y(2) receptor subtypes in the nucleus of the solitary tract (NTS), in the presence or absence of GAL(1-29), have been investigated. The effects of coinjections of GAL(1-29) and the NPY Y(1) agonist on the expression of c-FOS immunoreactivity in the NTS were also studied. The coinjection of NPY with GAL(1-29) induced a significant vasopressor and tachycardic action with a maximum 40% increase (P < 0.001). The coinjection of the NPY Y(1) agonist and GAL(1-29) induced a similar increase in mean arterial pressure and heart rate as did NPY plus GAL(1-29), actions that were not observed with the NPY Y(2) agonist plus GAL(1-29). GAL(1-29), 3 nm, significantly and substantially (by approximately 40%) decreased NPY Y(1) agonist binding in the NTS. This effect was significantly blocked (P < 0.01) in the presence of the specific galanin antagonist M35. The NPY Y(2) agonist binding was not modified in the presence of GAL(1-29). At the c-FOS level, the coinjection of NPY Y(1) and GAL(1-29) significantly reduced the c-FOS-immunoreactive response induced by either of the two peptides. The present findings suggest the existence of a modulatory antagonistic effect of GAL(1-29) mediated via galanin receptors on the NPY Y(1) receptor subtype and its signalling within the NTS.

Circulatory galanin levels increase severalfold with intense orthostatic challenge in healthy humans

The purpose of this study was to test the hypothesis that plasma galanin concentration (pGal) is regularly increased in healthy humans with extensive orthostatic stress. Twenty-six test persons (14 men, 12 women) were brought to an orthostatic end point via a progressive cardiovascular stress (PCS) protocol consisting of 70° head-up tilt plus increasing levels of lower body negative pressure until either hemodynamically defined presyncope or other signs of orthostatic intolerance occurred (nausea, clammy skin, excessive sweating, pallor of the skin). We further tested for possible gender, gravitational, and muscular training influences on plasma pGal responses: PCS was applied before and after 3 wk of daily vertical acceleration exposure training on a Human Powered Centrifuge. Test persons were randomly assigned to active (with bicycle work) or passive (without work) groups (seven men, six women in each group). Resting pGal was 26 ± 3 pg/ml in men and 39 ± 15 pg/ml in women (not significant); women had higher galanin responses (4.9-fold increase) than men (3.5-fold, P = 0.017) to PCS exposure. Overall, PCS increased pGal to 186 ± 5 pg/ml ( P = 0.0003), without significant differences between presyncope vs. orthostatic intolerance, pre- vs. postcentrifuge, or active vs. passive gravitational training. Increases in pGal were poorly related to synchronous elevations in plasma vasopressin. We conclude that galanin is regularly increased in healthy humans under conditions of presyncopal orthostatic stress, the response being independent of gravity training but larger in women than in men.

Role of galanin and galanin(1-15) on central cardiovascular control

Galanin and the N-terminal fragment Galanin(1-15) are involved in central cardiovascular regulation. The present paper reviews the recent cardiovascular results obtained by intracisternal injections of Galanin and Galanin(1-15) showing that: (A) the Galanin antagonist M40 blocks the central cardiovascular responses induced by Galanin(1-15) but not those elicited by Galanin; (B) both Galanin and Galanin(1-15) induce the expression of c-Fos in cardiovascular nuclei of the medulla oblongata with different temporal and spatial profiles; (C) the cardiovascular action of Galanin(1-15), but not Galanin, is mediated by peripheral beta-receptor stimulation; (D) and it is demonstrated an antagonistic Galanin/alpha2-adrenoceptors interaction as well as a differential modulation of central cardiovascular responses of Angiotensin II by Galanin or Galanin(1-15). All these data strengthen the involvement of both Galanin molecules as neuromodulators on central cardiovascular regulation.

Intracisternal galanin/angiotensin II interactions in central cardiovascular control

The aim of this work was to investigate the interactions between angiotensin II (Ang II) and galanin(1-29) [GAL(1-29)] or its N-terminal fragment galanin(1-15) [GAL(1-15)] on central cardiovascular control. The involvement of angiotensin type1 (AT1) receptor subtype was analyzed by the AT1 antagonist, DuP 753. Anesthesized male Sprague-Dawley rats received intracisternal microinjections of Ang II (3 nmol) with GAL(1-29) (3 nmol) or GAL(1-15) (0.1 nmol) alone or in combination. The changes in mean arterial pressure (MAP) and heart rate (HR) recorded from the femoral artery were analyzed. The injection of Ang II and GAL(1-15) alone did not produce any change in MAP. However, coinjections of both Ang II and GAL(1-15) elicited a significant vasopressor response. This response was blocked by DuP 753. Ang II and GAL(1-15) alone produced an increase in HR. The coinjections of Ang II with GAL(1-15) induced an increase in HR not significantly different from the tachycardia produced by each peptide. The presence of DuP 753 counteracted this response. GAL(1-29) alone elicited a transient vasopressor response that disappeared in the presence of Ang II. The coinjections of Ang II with GAL(1-29) and with DuP 753 restored the transient vasopressor effect produced by GAL(1-29). GAL(1-29) produced a slight but significant tachycardic effect that was not modified in the presence of Ang II. The presence of DuP 753 did not modify the tachycardic response produced by Ang II and GAL(1-29). These results give indications for the existence of a differential modulatory effect of Ang II with GAL(1-15) and GAL(1-29) on central blood pressure response that might be dependent on the activity of the angiotensin AT1 receptor subtype.

Decreases in the expression of CGRP and galanin mRNA in central and peripheral neurons related to the control of blood pressure following experimental hypertension in rats

Calcitonin gene-related peptide (alpha CGRP) and galanin (GAL) are peptides known to participate in central mechanisms of blood pressure control. Nonetheless, variations in the synthesis of the peptides in response to a hypertensive challenge are not well described, specially using a model, which allows acute and chronic analyses. In this study, we have employed in situ hybridization to analyse changes in mRNA expression of alpha CGRP and GAL in the nucleus tractus solitarii (NTS), hypothalamic paraventricular nucleus (PVN) as well as petrosal and nodose ganglia after aortic coarctation-induced hypertension in rats. Acute (2h) and chronic (3 and 7 days) analyses were performed in order to evaluate the involvement of both peptides in different periods of hypertension. The analysis of relative mRNA levels showed significant differences between sham-operated and aortic coarcted hypertensive rats. alpha CGRP mRNA expression was decreased 2h (40%) and 3 days (42%) in nodose and petrosal ganglia, respectively, after coarctation. No changes in CGRP mRNA signal were seen in the NTS and PVN in the analysed periods. GAL mRNA expression was decreased in the NTS (19%) and PVN (55%), 3 and 7 days, respectively, after coarctation-induced hypertension. No changes in GAL mRNA expression were observed in petrosal and nodose ganglia following aortic coarctation. Data suggest that alpha CGRP and GAL may participate in the mechanisms involved in the establishment/maintenance of hypertension induced by aortic coarctation. Acute changes might be involved with the adaptation to the hypertensive state, while changes at the chronic phase might be related to counteraction of hypertension.

Molecular mechanisms and therapeutical implications of intramembrane receptor/receptor interactions among heptahelical receptors with examples from the striatopallidal GABA neurons

The molecular basis for the known intramembrane receptor/receptor interactions among G protein-coupled receptors was postulated to be heteromerization based on receptor subtype-specific interactions between different types of receptor homomers. The discovery of GABAB heterodimers started this field rapidly followed by the discovery of heteromerization among isoreceptors of several G protein-coupled receptors such as delta/kappa opioid receptors. Heteromerization was also discovered among distinct types of G protein-coupled receptors with the initial demonstration of somatostatin SSTR5/dopamine D2 and adenosine A1/dopamine D1 heteromeric receptor complexes. The functional meaning of these heteromeric complexes is to achieve direct or indirect (via adapter proteins) intramembrane receptor/receptor interactions in the complex. G protein-coupled receptors also form heteromeric complexes involving direct interactions with ion channel receptors, the best example being the GABAA/dopamine D5 receptor heteromerization, as well as with receptor tyrosine kinases and with receptor activity modulating proteins. As an example, adenosine, dopamine, and glutamate metabotropic receptor/receptor interactions in the striatopallidal GABA neurons are discussed as well as their relevance for Parkinson's disease, schizophrenia, and drug dependence. The heterodimer is only one type of heteromeric complex, and the evidence is equally compatible with the existence of higher order heteromeric complexes, where also adapter proteins such as homer proteins and scaffolding proteins can exist. These complexes may assist in the process of linking G protein-coupled receptors and ion channel receptors together in a receptor mosaic that may have special integrative value and may constitute the molecular basis for some forms of learning and memory.

Plasma galanin response to head-up tilt in normal subjects and patients with recurrent vasovagal syncope

Neurohumoral factors may contribute to cardiovascular changes associated with vasovagal syncope (VVS). Galanin (GAL) is a neuropeptide, widely distributed in the central and peripheral nervous systems, that interacts with both sympathetic and vagal systems as well as with neurotransmitters, such as serotonin. We investigated the changes in plasma GAL and catecholamine levels during head-up tilt (HUT) test in patients with recurrent VVS. Twenty-two patients (11 women, aged 33.1 +/- 4.2 years) with a history of VVS and 10 healthy subjects (5 women, aged 38.0 +/- 5.8 years) underwent HUT test (60 degrees, 45 minutes). GAL and catecholamine plasma levels were measured in the supine position, during HUT and, in patients with positive response, at presyncope, syncope, and after recovery of consciousness. Thirteen patients developed syncope during HUT, whereas no healthy subjects had a positive response. In healthy subjects, GAL did not change during HUT. By contrast, in patients with a history of VVS and a negative response to tilting (no syncope), GAL significantly (P <.001) increased in response to tilting (supine, 10.2 +/- 0.6 pmol/L; tilting, 18.1 +/- 1.1 pmol/L at 45 minutes) and correlated positively with the increases in blood pressure (BP) and heart rate (HR). In patients with a positive response, GAL did not change either before the loss of consciousness or during syncope. In patients with a positive response, norepinephrine (NE) significantly (P <.001) increased during tilting and then remained practically unchanged during syncope, whereas epinephrine (E) significantly (P <.001) increased during tilting and then showed further significant increases at presyncope and syncope. In conclusion, this study shows that circulating GAL levels progressively increase in correlation with the cardiovascular parameters during a negative HUT in patients with a history of VVS, whereas they remain unchanged in healthy subjects. Moreover, in the patients with tilting-induced syncope GAL does not change either before or during loss of consciousness. These data suggest a role for endogenous GAL in the adaptive responses to acute orthostatic stress preventing syncope in susceptible individuals.

Propranolol blocks the tachycardia induced by galanin (1-15) but not by galanin (1-29)

The efferent pathways involved in the tachycardia induced by intracisternal injections of the N-terminal galanin fragment (1-15) (GAL (1-15)) and galanin (GAL (1-29)) has been evaluated in rats pretreated with the cholinergic antagonist atropine or the beta-antagonist propranolol. The pretreatment with propranolol significantly blocked the tachycardic and vasopressor effect produced by intracisternal injection of GAL (1-15) (p<0.05), but the pretreatment with atropine did not modify these cardiovascular effects. However, the cardiovascular response elicited by GAL (1-29) is modified by the pretreatment with atropine (p<0.05) but not by propranolol. These findings demonstrate that the central cardiovascular action of GAL (1-15), but not GAL (1-29), is mediated by beta-receptor stimulation and this suggests the existence of a different pathway involved in the cardiovascular response produced by the N-terminal galanin fragment as compared with the parent molecule GAL (1-29).

Central galanin and N-terminal galanin fragment induce c-Fos immunoreactivity in the medulla oblongata of the anesthetized rat

This immunohistochemical study analyzed the c-Fos expression (c-Fos-ir) induced by galanin injections. Galanin and N-terminal galanin fragment (1-15) induced a significant increase of c-Fos expression (c-ir) within the medulla oblongata 90 min and 6 h. after intracisternal injections. This expression has been studied mainly in the nucleus of the solitary tract and in the ventrolateral medulla showing different temporal profiles for both peptides. The presence of c-Fos-ir in TH-positive cells was analyzed in all the groups. These results may be relevant to understand the role of galanin in several functions including central cardiovascular control.

Galanin/alpha2-adrenoceptor interactions in telencephalic and diencephalic regions of the rat

The aim of this study was to evaluate whether galanin could affect central alpha2-adrenoceptors in telencephalic and diencephalic regions in the rat using quantitative receptor autoradiography with the alpha2 agonist radioligand [3H]p-aminoclonidine. Galanin 1 nM significantly and substantially increased the Kd value of the [3H]p-aminoclonidine binding sites in the medial hypothalamus and amygdala by 86% (p < 0.01) and 73% (p < 0.05) respectively. The Bmax value was only significantly increased with 3 nM galanin in the amygdala and the medial hypothalamus (both p < 0.05). The antagonist M35 counteracted the increase of the Kd values of the alpha2-adrenoceptor agonist binding sites produced by galanin 1 nM in the amygdala and the medial hypothalamus (both p < 0.001). These findings suggest the existence of an antagonistic galanin/alpha2 adrenoceptor interaction in the medial hypothalamus and amygdala that may be of relevance for alpha2-adrenoceptor-regulated neuroendocrine functions and food intake.

Antagonistic oxytocin/alpha2-adrenoreceptor interactions in the nucleus tractus solitarii: relevance for central cardiovascular control

The modulation of the central cardiovascular effects of alpha2-adrenoceptor activation by oxytocin in the nucleus tractus solitarii has been evaluated by cardiovascular analysis and by quantitative receptor autoradiography. Microinjections in the nucleus tractus solitarii of a threshold dose of oxytocin effectively and significantly counteracted the vasodepressor and bradycardic actions of an ED50 dose of the alpha2-adrenoceptor agonist clonidine. The coinjection of a threshold dose of oxytocin with a threshold dose of clonidine did not produce any changes in the mean arterial pressure but a tachycardic response was observed. Receptor autoradiographical experiments showed that oxytocin (3 nM) significantly increased the Kd and Bmax values of [3H]p-aminoclonidine binding sites in the nucleus tractus solitarii compatible with a possible antagonistic interaction with the alpha2-adrenoceptors, and this effect was blocked by the presence of the specific oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin. These findings suggest the existence of an antagonistic oxytocin/alpha2-adrenoceptor interaction in nucleus tractus solitarii that may be of relevance for the demonstrated modulation of alpha2-adrenoceptor induced cardiovascular responses by oxytocin.