Cardiovascular effects of calcitonin gene-related peptides I and II in man

Distribution and morphology of calcitonin gene-related peptide (CGRP) innervation in flat mounts of whole rat atria and ventricles

Calcitonin gene-related peptide (CGRP) is widely used as a marker for nociceptive afferent axons. However, the distribution of CGRP-IR axons has not been fully determined in the whole rat heart. Immunohistochemically labeled flat-mounts of the right and left atria and ventricles, and the interventricular septum (IVS) in rats for CGRP were assessed with a Zeiss imager to generate complete montages of the entire atria, ventricles, and septum, and a confocal microscope was used to acquire detailed images of selected regions. We found that 1) CGRP-IR axons extensively innervated all regions of the atrial walls including the sinoatrial node region, auricles, atrioventricular node region, superior/inferior vena cava, left pre-caval vein, and pulmonary veins. 2) CGRP-IR axons formed varicose terminals around individual neurons in some cardiac ganglia but passed through other ganglia without making appositions with cardiac neurons. 3) Varicose CGRP-IR axons innervated the walls of blood vessels. 4) CGRP-IR axons extensively innervated the right/left ventricular walls and IVS. Our data shows the rather ubiquitous distribution of CGRP-IR axons in the whole rat heart at single-cell/axon/varicosity resolution for the first time. This study lays the foundation for future studies to quantify the differences in CGRP-IR axon innervation between sexes, disease models, and species.

Mechanisms of QT prolongation by buprenorphine cannot be explained by direct hERG channel block

Buprenorphine is a μ-opioid receptor (MOR) partial agonist used to manage pain and addiction. QT_C prolongation that crosses the 10 msec threshold of regulatory concern was observed at a supratherapeutic dose in two thorough QT studies for the transdermal buprenorphine product BUTRANS^®. Because QT_C prolongation can be associated with Torsades de Pointes (TdP), a rare but potentially fatal ventricular arrhythmia, these results have led to further investigation of the electrophysiological effects of buprenorphine. Drug-induced QT_C prolongation and TdP are most commonly caused by acute inhibition of hERG current (I_hERG) that contribute to the repolarizing phase of the ventricular action potentials (APs). Concomitant inhibition of inward late Na⁺ (I_NaL) and/or L-type Ca²⁺ (I_CaL) current can offer some protection against proarrhythmia. Therefore, we characterized the effects of buprenorphine and its major metabolite norbuprenorphine on cardiac hERG, Ca²⁺, and Na⁺ ion channels, as well as cardiac APs. For comparison, methadone, a MOR agonist associated with QT_C prolongation and high TdP risk, and naltrexone and naloxone, two opioid receptor antagonists, were also studied. Whole cell recordings were performed at 37°C on cells stably expressing hERG, Ca_V1.2, and Na_V1.5 proteins. Microelectrode array (MEA) recordings were made on human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The results showed that buprenorphine, norbuprenorphine, naltrexone, and naloxone had no effect on I_hERG, I_CaL, I_NaL, and peak Na⁺ current (I_NaP) at clinically relevant concentrations. In contrast, methadone inhibited I_hERG, I_CaL, and I_NaL. Experiments on iPSC-CMs showed a lack of effect for buprenorphine, norbuprenorphine, naltrexone, and naloxone, and delayed repolarization for methadone at clinically relevant concentrations. The mechanism of QT_C prolongation is opioid moiety-specific. This remains undefined for buprenorphine, while for methadone it involves direct hERG channel block. There is no evidence that buprenorphine use is associated with TdP. Whether this lack of TdP risk can be generalized to other drugs with QT_C prolongation not mediated by acute hERG channel block warrants further study.

Neurohumoral Control of Sinoatrial Node Activity and Heart Rate: Insight From Experimental Models and Findings From Humans

The sinoatrial node is perhaps one of the most important tissues in the entire body: it is the natural pacemaker of the heart, making it responsible for initiating each-and-every normal heartbeat. As such, its activity is heavily controlled, allowing heart rate to rapidly adapt to changes in physiological demand. Control of sinoatrial node activity, however, is complex, occurring through the autonomic nervous system and various circulating and locally released factors. In this review we discuss the coupled-clock pacemaker system and how its manipulation by neurohumoral signaling alters heart rate, considering the multitude of canonical and non-canonical agents that are known to modulate sinoatrial node activity. For each, we discuss the principal receptors involved and known intracellular signaling and protein targets, highlighting gaps in our knowledge and understanding from experimental models and human studies that represent areas for future research.

Protective Role of α-Calcitonin Gene-Related Peptide in Cardiovascular Diseases

α-Calcitonin gene-related peptide (α-CGRP) is a regulatory neuropeptide of 37 amino acids. It is widely distributed in the central and peripheral nervous system, predominantly in cell bodies of the dorsal root ganglion (DRG). It is the most potent vasodilator known to date and has inotropic and chronotropic effects. Using pharmacological and genetic approaches, our laboratory and other research groups established the protective role of α-CGRP in various cardiovascular diseases such as heart failure, experimental hypertension, myocardial infarction, and myocardial ischemia/reperfusion injury (I/R injury). α-CGRP acts as a depressor to attenuate the rise in blood pressure in three different models of experimental hypertension: (1) DOC-salt, (2) subtotal nephrectomy-salt, and (3) L-NAME-induced hypertension during pregnancy. Subcutaneous administration of α-CGRP lowers the blood pressure in hypertensive and normotensive humans and rodents. Recent studies also demonstrated that an α-CGRP analog, acylated α-CGRP, with extended half-life (~7 h) reduces blood pressure in Ang-II-induced hypertensive mouse, and protects against abdominal aortic constriction (AAC)-induced heart failure. Together, these studies suggest that α-CGRP, native or a modified form, may be a potential therapeutic agent to treat patients suffering from cardiac diseases.

CGRP Discovery and Timeline

Calcitonin gene-related peptide (CGRP) was discovered over about 35 years ago through molecular biological techniques. Its activity as a vasodilator and the proposal that it was involved in pain processing were then soon established. Today, we are in the interesting situation of having the approval for the clinical use of antagonists and antibodies that have proved to block CGRP activities and benefit migraine. Despite all, there is still much to learn concerning the relevance of the vasodilator and other activities as well as further potential applications of CGRP agonists and blockers in disease. This review aims to discuss the history and present knowledge and to act as an introductory chapter in this volume.

Menopausal Hot Flashes: A Concise Review

Hot flashes (HFs), defined as transient sensations of heat, sweating, flushing, anxiety, and chills lasting for 1-5 min, constitute one of the most common symptoms of menopause among women though only a few seek treatment for these. The basis of HFs lies in abnormal hypothalamic thermoregulatory control resulting in abnormal vasodilatory response to minor elevations of core body temperature. Recent data suggest an important role for calcitonin gene-related peptide, hypothalamic kisspeptin, neurokinin B and dynorphin signal system, serotonin, norepinephrine in causation of HFs in addition to estrogen deficiency which plays a cardinal role. The mainstay of treatment includes hormonal replacement therapy, selective serotonin, and norepinephrine reuptake inhibitors in addition to lifestyle modification. In this review, we address common issues related to menopause HFs and suggest a stepwise approach to their management.

Nociceptor sensory neurons suppress neutrophil and γδ T cell responses in bacterial lung infections and lethal pneumonia

Nociceptor sensory neurons suppress innate immunity during bacterial lung infection.

Lung-innervating nociceptor sensory neurons detect noxious or harmful stimuli and consequently protect organisms by mediating coughing, pain, and bronchoconstriction. However, the role of sensory neurons in pulmonary host defense is unclear. Here, we found that TRPV1⁺ nociceptors suppressed protective immunity against lethal Staphylococcus aureus pneumonia. Targeted TRPV1⁺-neuron ablation increased survival, cytokine induction, and lung bacterial clearance. Nociceptors suppressed the recruitment and surveillance of neutrophils, and altered lung γδ T cell numbers, which are necessary for immunity. Vagal ganglia TRPV1⁺ afferents mediated immunosuppression through release of the neuropeptide calcitonin gene–related peptide (CGRP). Targeting neuroimmunological signaling may be an effective approach to treat lung infections and bacterial pneumonia.

A Novel α-Calcitonin Gene-Related Peptide Analogue Protects Against End-Organ Damage in Experimental Hypertension, Cardiac Hypertrophy, and Heart Failure

Supplemental Digital Content is available in the text.

Research into the therapeutic potential of α-calcitonin gene–related peptide (α-CGRP) has been limited because of its peptide nature and short half-life. Here, we evaluate whether a novel potent and long-lasting (t_½ ≥7 hours) acylated α-CGRP analogue (αAnalogue) could alleviate and reverse cardiovascular disease in 2 distinct murine models of hypertension and heart failure in vivo.

Relationship Between Migraine, Blood Pressure and Carotid Thickness. A Population-Based Study in the Elderly

The relationship between migraine and blood pressure is controversial. We studied the association between migraine and blood pressure in a population-based sample of elderly patients. Participants were 1373 subjects 59-71 years of age. Lifetime migraine was diagnosed according to the International Headache Society criteria by a headache specialist. Blood pressure was measured as well as the carotid intima-media thickness (IMT) which is a good marker of the long-term exposure to high blood pressure. Migraine during life was diagnosed in 140 participants. Mean systolic blood pressure was lower in subjects with migraine than in those without headache (128 mmHg vs. 137 mmHg). There was a significant trend of decreasing frequency of migraine with increasing blood pressure and also with increasing IMT. In this study, migraine was associated with lower levels of blood pressure and with smaller values of carotid wall thickness.

Migraine Patients have Lower Systolic but Higher Diastolic Blood Pressure Compared with Controls in a Population-Based Study of 21 537 Subjects. The Reykjavik Study

Several studies have explored a possible association between migraine and hyper- tension, with contradictory results. Because of this uncertainty the relation between blood pressure (BP) and migraine was studied in 10 366 men and 11 171 women in a population-based longitudinal study. A modified version of the 1988 International Headache Society criteria was used for diagnosis of migraine. Logistic regression analysis was used. The crude 1-year prevalence of migraine was 5.2% among men and 14.1% among women. No significant association was found between hypertension and migraine. For a one standard deviation (SD) increase in diastolic BP the probability of having migraine increased 14% ( P = 0.11) for men and 30% ( P < 0.0001) for women. For a 1-SD increase in systolic BP the probability of having migraine decreased 19% ( P = 0.007) for men and 25% ( P < 0.0001) for women. It was also found that for a 1-SD increase in pulse pressure the probability of having migraine decreased 13% ( P = 0.005) for men and 14% ( P < 0.0001) for women. In a population-based study of men and women it was found that subjects with migraine had lower pulse pressure, lower systolic BP and higher diastolic BP compared with controls.

Calcitonin Gene-Related Peptide Improves Hypoxia-Induced Inflammation and Apoptosis via Nitric Oxide in H9c2 Cardiomyoblast Cells

OBJECTIVES

The aim of this work was to investigate whether calcitonin gene-related peptide (CGRP) plays a protective role in cardiomyocytes against hypoxia-induced inflammation and apoptosis via an NO-mediated pathway.

METHODS

H9c2 cardiac cells were exposed to hypoxia for 2 h to establish a model of myocardial hypoxic-ischemic injury. The cells were pretreated with either CGRP or nitric oxide synthase (NOS) inhibitor (L-NAME) before being exposed to hypoxia for 30 min. Cell viability was analyzed using a cell counter kit 8 (CCK-8). The levels of IL-6 and TNF-α were determined by the corresponding enzyme-linked immunosorbent assay. The expression levels of several apoptosis proteins (p53, caspase-3, cytochrome C) and NOS were detected by Western blot assays. An NO kit was used to evaluate the production of NO.

RESULTS

Pretreatment of H9c2 cardiac cells with CGRP for 30 min prior to exposure to hypoxia markedly improved cell viability (83.57 ± 3.21 vs. 62.83 ± 8.30%, p < 0.001); the same effect was observed following pretreatment with the NOS inhibitor L-NAME (89.34 ± 5.95 vs. 75.01 ± 5.61%, p < 0.01). Pretreatment with CGRP also significantly attenuated the inflammatory responses induced by hypoxia, as evidenced by decreases of the levels of both IL-6 (193.21 ± 13.54 vs. 293.38 ± 56.49%, p < 0.001) and TNF-α (207.71 ± 44.27 vs. 281.46 ± 64.88%, p < 0.001). Additionally, CGRP significantly decreased the hypoxia-induced overexpression of the apoptotic proteins (p53: 0.27 ± 0.10 vs. 0.87 ± 0.30, p < 0.001; caspase-3: 0.65 ± 0.15 vs. 0.98 ± 0.26, p < 0.001; cytochrome C: 1.51 ± 0.39 vs. 2.80 ± 0.69, p < 0.001) and enhanced the expression of both endothelial NOS (eNOS; 0.59 ± 0.24 vs. 0.37 ± 0.14, p < 0.05) and phosphorylated eNOS (0.60 ± 0.13 vs. 0.40 ± 0.07, p < 0.05). Furthermore, the application of both L-NAME and CGRP attenuated the hypoxia-induced expression of inducible NOS (iNOS; p < 0.05) and enhanced a hypoxia-mediated decrease in NO (p < 0.01). Interestingly, the expression levels of cell apoptosis (p < 0.05), iNOS and eNOS (p < 0.05) were decreased with L-NAME and CGRP cotreatment following 2 h of acute hypoxia, but the apoptotic factors (p < 0.05) were increased compared with only CGRP pretreatment.

CONCLUSION

CGRP protects cardiomyocytes from hypoxia-induced inflammation and apoptosis by modulating NO production.

Inotropic and lusitropic effects of calcitonin gene-related peptide in the heart

Previous studies have demonstrated positive-inotropic effects of calcitonin gene-related peptide (CGRP), but the mechanisms remain unclear. Therefore, two experiments were performed to determine the physiological correlates of the positive-inotropic effects of CGRP. Treatments designed to antagonize the effects of physiologically active CGRP₁₋₃₇ included posttreatment with CGRP₈₋₃₇ and pretreatment with LY-294002 (LY, an inhibitor of phosphatidylinositol 3-kinase), 17β-estradiol (E), and progesterone (P) were also used to modulate the effects of CGRP₁₋₃₇. Experiment 1 was in vitro studies on sarcomeres and cells of isolated adult rat cardiac myocytes. CGRP₁₋₃₇, alone and in combination with E and P, decreased sarcomere shortening velocities and increased shortening percentages, effects that were antagonized by CGRP₈₋₃₇, but not by LY. CGRP₁₋₃₇ increased resting intracellular calcium ion concentrations and Ca(2+) influxes, effects that were also antagonized by both CGRP₈₋₃₇ and LY. Experiment 2 was in vivo studies on left ventricular pressure-volume (PV) loops. CGRP₁₋₃₇ increased end-systolic pressure, ejection fraction, and velocities of contraction and relaxation while decreasing stroke volume, cardiac output, stroke work, PV area, and compliance. After partial occlusion of the vena cava, CGRP₁₋₃₇ increased the slope of the end-systolic PV relationship. CGRP₈₋₃₇ and LY attenuated most of the CGRP-induced changes. These findings suggest that CGRP-induced positive-inotropic effects may be increased by treatments with estradiol and progesterone and inhibited by LY. The physiological correlates of CGRP-induced positive inotropy observed in rat sarcomeres, cells, and intact hearts are likely to reveal novel mechanisms of heart failure in humans.

Migraine and hypertension

Although the possibility of a comorbidity between migraine and hypertension has long been suspected, the epidemiologic evidence is controversial, with studies demonstrating positive, negative or no correlation between the two diseases. A unifying view that takes into account the most recent evidence suggests that there might be a different effect of diastolic and systolic pressure, with the former having a positive and the latter a negative correlation with migraine. In this paper, the methodologic and clinical reasons for the discrepancies in epidemiologic studies are discussed, together with the possible biological mechanisms that might account for the migraine-hypertension correlation. One such mechanisms may be the renin angiotensin system, which is certainly involved in hypertension and has activities in the CNS that may be relevant for migraine pathogenesis. Despite the uncertainty still present in this field, the control of hypertension in migraine patients is an important factor for the success of migraine treatment and to lower cerebrovascular risk.

Biochemistry and pharmacology of endovanilloids

Endovanilloids are defined as endogenous ligands and activators of transient receptor potential (TRP) vanilloid type 1 (TRPV1) channels. The first endovanilloid to be identified was anandamide (AEA), previously discovered as an endogenous agonist of cannabinoid receptors. In fact, there are several similarities, in terms of opposing actions on the same intracellular signals, role in the same pathological conditions, and shared ligands and tissue distribution, between TRPV1 and cannabinoid CB(1) receptors. After AEA and some of its congeners (the unsaturated long chain N-acylethanolamines), at least 2 other families of endogenous lipids have been suggested to act as endovanilloids: (i) unsaturated long chain N-acyldopamines and (ii) some lipoxygenase (LOX) metabolites of arachidonic acid (AA). Here we discuss the mechanisms for the regulation of the levels of the proposed endovanilloids, as well as their TRPV1-mediated pharmacological actions in vitro and in vivo. Furthermore, we outline the possible pathological conditions in which endovanilloids, acting at sometimes aberrantly expressed TRPV1 receptors, might play a role.

Stimulated release of calcitonin gene-related peptide from the human right atrium in patients with and without diabetes mellitus

Calcitonin gene-related peptide (CGRP), a potent vasodilator released during activation from a subset of sensory Adelta- and C-fiber afferents, has been suggested to play a beneficial role in myocardial ischemia. Variations in CGRP release can possibly be correlated with diseases that involve changes in activity or degeneration of cardiac afferent fibers. The aim of the present study was to examine basal and stimulated CGRP release from cardiac tissue in patients who underwent cardiopulmonary bypass surgery and to compare patients with and without known history of diabetes mellitus. Small pieces of the right atrium routinely excised during the bypass operations were passed through series of oxygenated solutions. The TRPV1 receptor agonist capsaicin and the nitric oxide donor NONOate were added for stimulation of cardiac afferent fibers. The eluates were processed using an enzyme immuno-assay (EIA) for measurement of CGRP concentrations. Both capsaicin and NONOate caused significant increases in CGRP release. No significant differences in CGRP release between patients with and without diabetes mellitus were examined. The present study evaluates a simple and reproducible model for measuring stimulated CGRP release from the human right atrium.

Calcitonin deficiency in mice progressively results in high bone turnover

Although the pharmacological action of calcitonin (CT) as an inhibitor of bone resorption is well established, there is still some controversy regarding its physiological function. Unexpectedly, Calca-deficient mice lacking CT and alpha-calcitonin gene-related peptide (alphaCGRP) were described to have a high bone mass phenotype caused by increased bone formation with normal bone resorption. Here we show that these mice develop a phenotype of high bone turnover with age, suggesting that CT is a physiological inhibitor of bone remodeling.

INTRODUCTION

The absence of significant changes in bone mineral density caused by decline or overproduction of CT in humans has raised the question, whether the pharmacological action of CT as an inhibitor of bone resorption is also of physiological relevance. To study the physiological role of mammalian CT, we have analyzed the age-dependent bone phenotype of two mouse models, one lacking CT and alphaCGRP (Calca-/-), the other one lacking only alphaCGRP (alphaCGRP-/-).

MATERIALS AND METHODS

Bones from wildtype, Calca-/- -mice and alphaCGRP-/- -mice were analyzed at the ages of 6, 12 and 18 months using undecalcified histology. Differences of bone remodeling were quantified by static and dynamic histomorphometry as well as by measuring the urinary collagen degradation products. To rule out secondary mechanisms underlying the observed phenotype, we determined serum concentrations of relevant hormones using commercially available antibody-based detection kits.

RESULTS

Whereas alphaCGRP-/- -mice display an osteopenia at all ages analyzed, the Calca-/- -mice develop a phenotype of high bone turnover with age. Histomorphometric analysis performed at the age of 12 months revealed significant increases of bone formation and bone resorption specifically in the Calca-/- -mice. This severe phenotype that can result in hyperostotic lesions, can not be explained by obvious endocrine abnormalities other than the absence of CT.

CONCLUSIONS

In addition to the previously described increase of bone formation in the Calca-deficient mice, we have observed that there is also an increase of bone resorption with age. This suggests that CT has a dual action as an inhibitor of bone remodeling, which may explain why alterations of CT serum levels in humans do not result in major changes of bone mineral density.

CGRP stimulates gill carbonic anhydrase activity in molluscs via a common CT/CGRP receptor

The physiological significance of calcitonin gene-related peptide (CGRP) during biomineralization was investigated by assessing the effect of human CGRP on the carbonic anhydrase activity in gill membranes of the pearl oyster, Pinctada margaritifera. Salmon CT and human CGRP were able to induce a 150% increase of the basal activity. No additive effect was observed suggesting that both activities are mediated by the same receptor. The CGRP-stimulated effect was specific as demonstrated by the inhibition produced by the CGRP antagonist, hCGRP8-37. So, CGRP by its specific action on gill carbonic anhydrase controls the calcification process, an ancient role both in invertebrates and non-mammalian vertebrates.

Release of calcitonin gene-related peptide from the isolated mouse heart: methodological validation of a new model

Calcitonin gene-related peptide (CGRP), a potent vasodilator released from a subset of sensory Adelta- and C-fiber afferents, has been suggested to play a beneficial role in myocardial ischemia. Variations in CGRP release can possibly be correlated with diseases that involve changes in activity or degeneration of cardial afferent fibers. The aim of the present study was to evaluate a simple and easily reproducible model for measuring stimulated CGRP release from cardial afferents. For this reason freshly isolated mouse hearts were passed through incubations in series of 25 min. Solutions consisting of oxygenated synthetic interstitial fluid. Dissolved substances such as capsaicin, bradykinin and potassium chloride were used as excitatory test stimuli. For comparison, isolated mouse hearts were perfused with the same solutions through a cannula inserted into the rising aorta. The eluates were processed using an enzyme immuno-assay for measurement of CGRP concentrations. Capsaicin, bradykinin and the potassium solution caused concentration-dependent increases in CGRP release. There were no differences in CGRP release when oxygen was replaced by nitrogen in the solutions. Immersion of hearts caused significantly more CGRP release than perfusion with same solutions. The results suggest that mouse heart immersion is more effective than coronary perfusion in measuring stimulated CGRP release from cardial afferents which are widely distributed in the epicardium but rare in deeper myocardial layers. The results are discussed with respect to the potentially important vasodilatory and cardioprotective functions of CGRP released from activated epicardial afferents.

Fish and Shellfish Upgrading, Traceability

Recognition of the limited biological resources and the increasing environmental pollution has emphasised the need for better utilisation of by-products from the fisheries. Currently, the seafood industry is dependent on the processing of the few selected fish and shellfish species that are highly popular with consumers but, from economic and nutritional points of view, it is essential to utilise the entire catch. In this review, we will focus on recent developments and innovations in the field of underutilised marine species and marine by-product upgrading and, more precisely, on two aspects of the bioconversion of wastes from marine organisms, i.e. extraction of enzymes and preparation of protein hydrolysates. We will deal with the question of accurate determination of fish species at the various steps of processing. Methods of genetic identification applicable to fresh fish samples and to derived products will be described.

Calcitonin gene-related peptide antagonism attenuates the haemodynamic and glycaemic responses to acute hypoxaemia in the late gestation sheep fetus

The fetal defence to acute hypoxaemia involves cardiovascular and metabolic responses, which include peripheral vasoconstriction and hyperglycaemia. Both these responses are mediated via neuroendocrine mechanisms, which require the stimulation of the sympathetic nervous system. In the adult, accumulating evidence supports a role for calcitonin gene-related peptide (CGRP) in the activation of sympathetic outflow. However, the role of CGRP in stimulated cardiovascular and metabolic functions before birth is completely unknown. This study tested the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence responses to acute hypoxaemia by affecting sympathetic outflow. Under anaesthesia, five sheep fetuses at 0.8 of gestation were surgically instrumented with catheters and a femoral arterial Transonic flow-probe. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. Arterial samples were taken for blood gases, metabolic status and hormone analyses. CGRP antagonism did not alter basal arterial blood gas, metabolic, cardiovascular or endocrine status. During hypoxaemia, similar falls in Pa,O2 occurred in all fetuses. During saline infusion, hypoxaemia induced hypertension, bradycardia, femoral vasoconstriction, hyperglycaemia and an increase in haemoglobin, catecholamines and neuropeptide Y (NPY). In contrast, CGRP antagonism markedly diminished the femoral vasoconstrictor and glycaemic responses to hypoxaemia, and attenuated the increases in haemoglobin, catecholamines and NPY. Combined, these results strongly support the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence to hypoxaemia by affecting sympathetic outflow.

The effects of CGRP on calcium transients of dedifferentiating cultured adult rat cardiomyocytes compared to non-cultured adult cardiomyocytes: possible protective and deleterious results in cardiac function

CGRP has potent cardiovascular effects but its role in heart failure is unclear. Effects of CGRP on calcium concentrations in fresh adult rat cardiomyocytes, cultured adult cardiomyocytes and neonatal cardiomyocytes were determined by real time fluorescence spectrophotometry. Treatment of cultured adult cardiomyocytes with CGRP resulted in a rapid cessation of beating and a reduction in intracellular calcium. Similar results were obtained in cultured neonatal myocytes. However, rod-shaped adult cardiomyocytes revealed a number of responses; (a) non-beating cells began to beat with increased intracellular calcium; (b) spontaneously beating cells exhibited increased intracellular calcium content and a faster beating rate or (c), myocytes increased their beating rate and became arrhythmic, suggesting that CGRP action on cultured dedifferentiated adult and neonatal myocytes depletes intracellular calcium, whereas in the rod-shaped mature myocytes calcium is retained, pointing to a different mode of action for CGRP on developing and dedifferentiating cardiomyocytes, compared to fully developed cardiomyocytes.

Calcitonin gene-related peptide contributes to the umbilical haemodynamic defence response to acute hypoxaemia

Despite clinical advances in obstetric practice, undiagnosed fetal hypoxaemia still contributes to a high incidence of perinatal morbidity. The fetal defence to hypoxaemia involves a redistribution of blood flow away from peripheral circulations towards essential vascular beds, such as the umbilical, cerebral, myocardial and adrenal circulations. In marked contrast to other essential vascular beds, the mechanisms mediating maintained perfusion of the umbilical circulation during hypoxaemia remain unknown. This study determined the role of calcitonin gene-related peptide (CGRP) in the maintenance of umbilical blood flow during basal and hypoxaemic conditions. Under anaesthesia, five sheep fetuses were instrumented with catheters and a Transonic probe around an umbilical artery, inside the fetal abdomen, at 0.8 of gestation. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. The CGRP antagonist did not alter basal blood gas or cardiovascular status in the fetus. A similar fall in Pa,O2 occurred in fetuses during either saline (21 +/- 0.8 to 9 +/- 0.9 mmHg) or antagonist treatment (20 +/- 0.9 to 9 +/- 1.2 mmHg). Hypoxaemia during saline led to significant increases in arterial blood pressure, umbilical blood flow and umbilical vascular conductance. In marked contrast, hypoxaemia during CGRP antagonist treatment led to pronounced falls in both umbilical blood flow and umbilical vascular conductance without affecting the magnitude of the hypertensive response. In conclusion, CGRP plays an important role in the umbilical haemodynamic defence response to hypoxaemia in the late gestation fetus.

Effects of the calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS on alpha-CGRP-induced regional haemodynamic changes in anaesthetised rats

Several studies suggest that a calcitonin gene-related peptide (CGRP) receptor antagonist may have antimigraine properties, most probably via the inhibition of CGRP-induced cranial vasodilatation. We recently showed that the novel selective CGRP receptor antagonist, BIBN4096BS (1-piperidinecarboxamide, -N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl] carbonyl] pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl) methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-, [[R-(R,(R*,S*)]), attenuated the CGRP-induced porcine carotid vasodilatation in a model predictive of antimigraine activity. In order to evaluate the potential safety of BIBN4096BS in migraine therapy, this study was designed to investigate the effects of intravenous BIBN4096BS on alpha-CGRP-induced systemic and regional haemodynamic changes in anaesthetised rats, using radioactive microspheres. In vehicle-pretreated animals, consecutive intravenous infusions of alpha-CGRP (0.25, 0.5 and 1 microg kg(-1) min.(-1)) dose-dependently decreased mean arterial blood pressure with an accompanying increase in heart rate and systemic vascular conductance whereas cardiac output remained unchanged. Alpha-CGRP also increased the vascular conductance to the heart, brain, gastrointestinal tract, adrenals, skeletal muscles and skin, whilst that to the kidneys, spleen, mesentery/pancreas and liver remained unaltered. The above systemic and regional haemodynamic responses to alpha-CGRP were clearly attenuated in BIBN4096BS (3 mg kg(-1) intravenously)-pretreated animals. These results indicate that exogenously administered alpha-CGRP dilates regional vascular beds via CGRP receptors on the basis of the antagonism produced by BIBN4096BS. Moreover, the fact that BIBN4096BS did not alter baseline haemodynamics suggests that endogenously produced CGRP does not play an important role in regulating the systemic and regional haemodynamics under resting conditions.

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS blocks CGRP and adrenomedullin vasoactive responses in the microvasculature

Calcitonin gene-related peptide (CGRP) is a potent microvascular dilator neuropeptide that is considered to play an essential role in neurogenic vasodilatation and in maintaining functional integrity in peripheral tissues. We have examined the effect of the nonpeptide CGRP antagonist BIBN4096BS on responses to CGRP and the structurally related peptide adrenomedullin, AM, in murine isolated aorta and mesentery preparations, and in the cutaneous microvasculature in vivo. We show for the first time that BIBN4096BS is an effective antagonist of CGRP and AM responses in the murine mesenteric and cutaneous microvasculature, and of CGRP in the murine aorta. After local administration, BIBN4096BS selectively inhibits the potentiation of microvascular permeability in the cutaneous microvasculature by CGRP and AM, with no effect on responses induced by other microvascular vasodilators. BIBN4096BS reversed both newly developed and established vasoactive responses induced by CGRP. The ability of CGRP to potentiate plasma extravasation was lost when coinjected with compound 48/80 (where mast cells would be activated to release proteases), but regained when soybean trypsin inhibitor was coinjected with compound 48/80. These results demonstrate that BIBN4096BS is a selective antagonist of responses induced by CGRP and AM in the mouse microvasculature, and CGRP in the mouse aorta. The ability of BIBN4096BS to block an established CGRP microvascular vasodilatation indicates that the sustained vasodilator activity of CGRP is due to the retention of the active intact peptide and the continued involvement of the CGRP receptor.

Activation of Capsaicin-Sensitive Sensory Neurons by Carvedilol, a Nonselective β-Blocker, in Spontaneous Hypertensive Rats

We performed a study in spontaneous hypertensive rats (SHR) to determine whether carvedilol, a nonselective beta-adrenoceptor antagonist, activates capsaicin-sensitive sensory neurons (CSSNs), thereby promoting the release of calcitonin gene-related peptide (CGRP), a neuropeptide with an important role in maintenance of cardiovascular homeostasis. Carvedilol given intravenously at a dose of 0.3 mg/kg transiently decreased the mean arterial blood pressure (MABP) and increased renal tissue blood flow with increases in CGRP levels in plasma and kidney. These effects induced by carvedilol were not seen in animals pretreated with capsazepine, an antagonist of capsaicin. Although 1.0 mg/kg cavedilol markedly decreased MABP, it neither increased renal tissue blood flow nor CGRP levels in plasma and kidney. Prazosin, a selective alpha(1)-adrenoceptor antagonist, and bisoprolol, a selective beta(1)-adrenoceptor antagonist, decreased MABP with capsazepine, showing no antagonistic action in either cases, and these agents increased neither renal tissue blood flow nor levels of CGRP in plasma and kidney. Both ICI 118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol], a selective beta(2)-adrenoceptor antagonist, at a dose of 0.25 mg/kg and capsaicin mimicked effects induced by 0.3 mg/kg carvedilol. Administration of 1.0 mg/kg ICI 118,551 produced effects similar to those induced by 1.0 mg/kg carvedilol. These observations strongly suggested that the low dose of carvedilol might activate CSSNs in SHR to increase the release of CGRP, thereby decreasing blood pressure with an increase in renal tissue blood flow. The effects induced by carvedilol seemed to be mediated by its beta(2)-adrenoceptor blockade activity.

Changes in calcitonin gene-related peptide, atrial natriuretic peptide and brain natriuretic peptide in patients undergoing coronary artery bypass grafting

The initiation of cardiopulmonary bypass creates significant derangements in cardiovascular volume status and both endocrine and autonomic nervous system function. To examine whether such derangements might differ in patients with different pre-operative physical status scores, we measured the plasma concentrations of calcitonin gene-related peptide, atrial natriuretic peptide and brain natriuretic peptide, catecholamines and antidiuretic hormone, as well as haemodynamic variables, during and after cardiopulmonary bypass in 27 consecutive patients undergoing coronary artery bypass grafting. The pre-operative levels of atrial natriuretic peptide and brain natriuretic peptide differed significantly between ASA II patients and III and IV patients [mean (SD) brain natriuretic peptide levels = 14 (8.2) vs. 129 (51) pg.ml-1]. Plasma calcitonin gene-related peptide increased significantly in both groups after the initiation of cardiopulmonary bypass, and remained increased throughout cardiopulmonary bypass. The changes in plasma epinephrine, norepinephrine and antidiuretic hormone were similar to those reported previously. The changes in plasma calcitonin gene-related peptide, atrial natriuretic peptide and brain natriuretic peptide did not correlate with any changes in haemodynamic variables before or after cardiopulmonary bypass. Measurement of plasma brain natriuretic peptide might usefully be included in the pre-operative evaluation of patients with cardiac disease.

Migraine is more frequent in individuals with optimal and normal blood pressure: a population-based study

BACKGROUND

The notion that hypertension causes headache is widely accepted despite the absence of confirmation by well-designed studies.

OBJECTIVE

To investigate the association between headache, characterized as tension type and migraine like, with blood pressure and hypertension.

METHODS

In a cross-sectional study we evaluate this association in a sample of 1174 individuals older than 17 years, representative of inhabitants of Porto Alegre, RS, Brazil. Headache and its subtypes were defined according to International Headache Society criteria. Hypertension was defined as the mean of two blood pressure readings >or=140/90 mmHg or use of antihypertensive drugs.

RESULTS

Headache in lifetime, in the last year, and defined as episodic and chronic tension-type headache was not associated with hypertension. Individuals with optimal or normal blood pressure (Sixth Joint National Committee criteria) complained of migraine more frequently than the participants with high-normal blood pressure or hypertension. This association persisted after adjustment for several potential confounding factors (risk ratio, 0.56; confidence interval, 0.41-0.77).

CONCLUSION

Our findings confirm that high blood pressure is not associated with the complaint of headache in the population. Individuals with migraine-like episodes of headache may have lower blood pressure than individuals without headache.

Regional hemodynamic effects of adrenomedullin in Wistar rats: a comparison with calcitonin gene-related peptide

Because both vasodilation induced by adrenomedullin (AM) and that induced by calcitonin gene-related peptide (CGRP) may occur via the same receptor, the two peptides might play similar roles in circulation. To examine this possibility, we used the colored microsphere technique and an ultrasonic flowmeter to investigate the systemic and regional effects of an equivalent dose (650 pmol/l) of AM and CGRP in conscious Wistar rats. AM significantly decreased mean arterial pressure and peripheral resistance but increased heart rate and cardiac index (CI). On the other hand, hypotension induced by CGRP was not accompanied by an increment in Cl. Both AM and CGRP increased the femoral arterial blood flow measured by the flowmeter, with the increase by AM being significantly larger. The regional hemodynamic effects were quite different between the two peptides. AM increased the blood flow in the heart, lungs, kidneys, adrenal glands, and spleen, whereas CGRP increased blood flow only in the heart. On the other hand, CGRP increased the cutaneous and gastric blood flows, which were not affected by AM. These differences in the regional vasodilatory effects of AM and CGRP suggest that the two peptides do not play similar roles in circulatory regulation.

Calcitonin gene-related peptide is not essential for the development of pressure overload-induced hypertrophy in vivo

The regulatory neuropeptide calcitonin-gene related peptide (CGRP) has been shown to evoke a hypertrophic response in isolated cardiomyocytes in vitro, an effect which was attributed to PKC activation. Activation of PKC has previously been implicated in the development of cardiac hypertrophy. We therefore investigated the role of CGRP in pressure overload-induced hypertrophy in vivo, which has not previously been reported. Constriction of the ascending aorta of rats resulted in an increase in the heart weight to body weight ratio, increased myocyte diameter, re-expression of the fetal genes ANF, MHCbeta and skeletal alpha-actin, and decreased expression of the adult genes GLUT4 and SERCA2a. Treatment of neonatal rat pups (1-2 days old) with capsaicin (50 mg/kg), resulted in the permanent de-afferentation of small-diameter unmyelinated CGRP-containing sensory C-fibres. Such treatment caused a 68% decrease in the CGRP-like immunoreactivity of hearts isolated from 10 week old rats (p < 0.001). Contrary to expectations, aortic constriction of capsaicin treated rats had no effect on the development of hypertrophy at the trophic, morphometric or gene expression levels. The results suggest that the development of pressure overload-induced hypertrophy in vivo does not require the regulatory neuropeptide CGRP.

Nitroxyl anion exerts redox-sensitive positive cardiac inotropy in vivo by calcitonin gene-related peptide signaling

Nitroxyl anion (NO(-)) is the one-electron reduction product of nitric oxide (NO( small middle dot)) and is enzymatically generated by NO synthase in vitro. The physiologic activity and mechanism of action of NO(-) in vivo remains unknown. The NO(-) generator Angeli's salt (AS, Na(2)N(2)O(3)) was administered to conscious chronically instrumented dogs, and pressure-dimension analysis was used to discriminate contractile from peripheral vascular responses. AS rapidly enhanced left ventricular contractility and concomitantly lowered cardiac preload volume and diastolic pressure (venodilation) without a change in arterial resistance. There were no associated changes in arterial or venous plasma cGMP. The inotropic response was similar despite reflex blockade with hexamethonium or volume reexpansion, indicating its independence from baroreflex stimulation. However, reflex activation did play a major role in the selective venodilation observed under basal conditions. These data contrasted with the pure NO donor diethylamine/NO, which induced a negligible inotropic response and a more balanced veno/arterial dilation. AS-induced positive inotropy, but not systemic vasodilatation, was highly redox-sensitive, being virtually inhibited by coinfusion of N-acetyl-l-cysteine. Cardiac inotropic signaling by NO(-) was mediated by calcitonin gene-related peptide (CGRP), as treatment with the selective CGRP-receptor antagonist CGRP(8-37) prevented this effect but not systemic vasodilation. Thus, NO(-) is a redox-sensitive positive inotrope with selective venodilator action, whose cardiac effects are mediated by CGRP-receptor stimulation. This fact is evidence linking NO(-) to redox-sensitive cardiac contractile modulation by nonadrenergic/noncholinergic peptide signaling. Given its cardiac and vascular properties, NO(-) may prove useful for the treatment of cardiovascular diseases characterized by cardiac depression and elevated venous filling pressures.

The effect of calcitonin gene-related peptide on pancreatic blood flow and secretion in conscious dogs

The effects of human alpha-calcitonin gene-related peptide (alpha-CGRP) and beta-CGRP on pancreatic arterial (PA), superior mesenteric (SMA) and left gastric arterial (LGA) blood flows were studied by ultrasound transit-time blood flow meters in five conscious dogs. Intravenous injections of alpha-CGRP and beta-CGRP (5-200 pmol/kg) induced a dose-related increase in PA flow and a dose-related decrease in its resistance. At lower doses, alpha-CGRP was more potent than beta-CGRP, but their maximal responses were similar. The blood flow responses to alpha-CGRP (200 pmol/kg) were 153% of the basal flow in LGA, 313% in PA, and 534% in SMA, while those to VIP (100 pmol/kg) were 467% in LGA, 953% in PA and 163% in SMA. Somatostatin reduced blood flow in all arteries. alpha-CGRP, but not beta-CGRP, at higher doses induced gastric contractions and pancreatic protein-rich secretion, which were blocked by atropine. These results suggest that CGRP in perivascular nerves in the pancreas may regulate pancreatic blood flow in dogs but its physiological function remains to be studied.

Calcitonin gene-related peptide (CGRP) expression in the human neonatal paravertebral ganglia

The distribution of calcitonin gene-related peptide-immunoreactivity (CGRP-IR) in human neonatal paravertebral ganglia was demonstrated by the method of indirect immunohistochemistry. A marked population (up to 21%) of CGRP-IR neurons and varicose nerve fibres was observed. The number of calcionin gene-related peptide-immunoreactive neurons varied from ganglion to ganglion in the sympathetic trunk. In addition to its cotransmitter functions, the existence of CGRP in neonatal ganglionic nerve cells was suggested by its inductive and trophic actions on the growth and differentiation of neurons.

Calcitonin and calcitonin gene-related peptide in the human prostate gland

BACKGROUND

Calcitonin-related peptides have been found in the human prostate, and calcitonin (CT) and calcitonin gene-related peptide (CGRP) have been demonstrated in subpopulations of neuroendocrine (NE) cells. The purpose of this study was to determine the concentrations of CT and CGRP as well as the densities of NE cells in normal prostates, benign prostatic hyperplasia (BPH), and carcinoma of the prostate (CAP).

METHODS

In 42 specimens of radical prostatectomy, the number of CT- and CGRP-immunoreactive NE cells in areas of normal and BPH tissue was determined, and compared with CAP tissue using immunocytochemistry. In addition, by radioimmunoassay (RIA), tissue levels of CT and CGRP were analyzed in extracts from areas of normal, BPH, and CAP tissue, as verified by adjacent histologic sections.

RESULTS

A significant decrease in CT-immunoreactive NE cells was observed in hyperplastic nodules of BPH in comparison to normal tissue. These findings were in parallel with a significant reduction in tissue CT level in BPH compared to normal tissue. There was also a marked, but statistically nonsignificant, reduction in CT levels in CAP tissue. In contrast, levels of CGRP in BPH and CAP tissue did not show any significant differences compared to normal tissue.

CONCLUSIONS

CT and CGRP are present in NE cells of the human prostate. Calcitonin levels are significantly reduced in BPH, in parallel with a decreased number of CT-immunoreactive NE cells, whereas no significant changes in tissue levels of CGRP were observed. The functional significance of these findings is discussed.

Positive inotropy mediated via CGRP receptors in isolated human myocardial trabeculae

Isometric contractile force were studied on isolated human myocardial trabeculae that were paced at 1.0 Hz in tissue baths. Alpha calcitonin gene-related peptide (alpha-CGRP) had a potent positive inotropic effect in most trabeculae from both the right atrium and left ventricle, and this effect was partially antagonized by the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M). Amylin and the CGRP(2) receptor agonist [Cys(acetylmethoxy)(2, 7)]CGRP had a positive inotropic effect in some trabeculae, whereas adrenomedullin had no inotropic effect. Using reverse transcriptase-polymerase chain reaction (PCR) mRNAs encoding the human calcitonin receptor-like receptor and the receptor associated modifying proteins (RAMPs) RAMP1, RAMP2, and RAMP3 were detected in human myocardial trabeculae from both the right atrium and left ventricle. In conclusion, functional CGRP(1) and CGRP(2) receptors may mediate a positive inotropic effect at both the atrial and ventricular level of the human heart. mRNAs for calcitonin receptor-like receptor and specific RAMPs further support the presence of CGRP receptors.

Positive inotropy of calcitonin gene-related peptide and amylin on porcine isolated myocardium

Isolated porcine myocardial trabeculae from right atria and left ventricles were paced at 1.5 Hz in tissue baths, and changes in isometric contractile force upon exposure to agonist were studied. Alpha calcitonin gene-related peptide (alpha-CGRP) increased contractile force in nearly half of the trabeculae, whereas the selective CGRP(2) receptor agonist [Cys(acetylmethoxy)(2,7)]-CGRP had effect in only a few. Preincubation with the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M) almost completely blocked positive inotropic responses to alpha-CGRP. Amylin had weak positive inotropic effects in some atrial, but not in ventricular trabeculae. Adrenomedullin did not affect contractility in either atrial or ventricular trabeculae. In conclusion, these results suggest that alpha-CGRP has a positive inotropic effect that can be mediated by both CGRP(1) and CGRP(2) receptors. Amylin seems to have a potential positive inotropic effect on atrial tissue, whereas no direct effect of adrenomedullin could be measured.

Mice lacking alpha-calcitonin gene-related peptide exhibit normal cardiovascular regulation and neuromuscular development

alpha-Calcitonin gene-related peptide (alphaCGRP) is a pleiotropic peptide neuromodulator that is widely expressed throughout the Central and peripheral nervous systems. CGRP has been implicated in a variety of physiological processes including peripheral vasodilation, cardiac acceleration nicotinic acetylcholine receptor (AChR) synthesis and function, testicular descent, nociception, carbohydrate metabolism, gastrointestinal motility, neurogenic inflammation, and gastric acid secretion. To provide a better understanding of the physiological role(s) mediated by this peptide neurotransmitter, we have generated alphaCGRP-null mice by targeted modification in embryonic stem cells. Mice lacking alpha CGRP expression demonstrate no obvious phenotypic differences from their wild-type littermates. Detailed analysis of systemic cardiovascular function revealed no differences between control and mutant mice regarding heart rate and blood pressure under basal or exercise-induced conditions and subsequent to pharmacological manipulation. Characterization of neuromuscular junction in morphology including nicotinic receptor localization, terminal sprouting in response to denervation, developmental regulation of AChR subunit expression, and synapse elimination also revealed no differences in alphaCGRP-deficient animals. These results suggest that alphaCGRP is not required for the systemic regulation of cardiovascular hemodynamics or development of the neuromuscular junction.

Ca2+-induced Ca2+ release involved in positive inotropic effect mediated by CGRP in ventricular myocytes

To investigate the effects and mechanisms of calcitonin gene-related peptide (CGRP) on ventricular contractility, ventricular myocytes isolated from adult rat and mouse hearts were exposed to CGRP. Myocyte contractility was assessed by a video edge motion detector, and the intracellular [Ca2+] transients were measured by a spectroflurophotometer in fura 2-loaded myocytes. CGRP exerted a potent concentration-dependent (10 pM-10 nM, EC50 = 44.1 pM) positive inotropism on rat ventricular myocytes. CGRP (1 nM) increased cell shortening during contraction by 140 +/- 40% above baselines and increased maximum velocity of contraction and relaxation by 98 and 106%, respectively. CGRP failed to produce any response in the presence of the CGRP1 receptor antagonist. CGRP induced similar inotropic response in mouse ventricular myocytes. CGRP increased the amplitude of [Ca2+] transients of ventricular myocytes by 120 +/- 25% above baseline and shortened the time of half-maximum myoplasmic Ca2+ clearance by 30 +/- 5%. Increase in intracellular Ca2+ mobilization by CGRP was dependent on Ca2+ influx through the activation of the L-type Ca2+ channel, because nifedipine blocked the CGRP-induced increase in [Ca2+] transients. Furthermore, CGRP failed to increase [Ca2+] transients after the inhibition of protein kinase A in ventricular myocytes. These data indicate that stimulation of mammalian ventricular myocardial CGRP1 receptors enhances [Ca2+] transients through the activation of protein kinase A, which in turn activates voltage-dependent L-type Ca2+ channels. These events lead to Ca2+-induced intracellular Ca2+ release and enhanced myocyte contraction and facilitated relaxation.

Haemodynamic and catecholamine responses to calcitonin gene-related peptide during volatile anaesthesia

PURPOSE

Calcitonin gene-related peptide (CGRP) produces vasodilatation, hypotension, and tachycardia. Tachycardia induced by CGRP may be due to sympathetic activation. Volatile anaesthetics attenuate activation of arterial baroreflexes. We examined the haemodynamic and endocrine effects of CGRP infusion (4 micrograms.kg-1) during anaesthesia with either enflurane or isoflurane in dogs.

METHODS

Measurements of haemodynamic variables and hormone assays for plasma catecholamines were made before, during, and after CGRP infusion. Anaesthesia consisted of induction with 25 mg.kg-1 pentobarbital, followed by either enflurane (n = 7) or isoflurane (n = 7) to achieve a 1.0 end-tidal minimum alveolar concentration in oxygen 100%.

RESULTS

Mean arterial pressure and systemic vascular resistance decreased (P < 0.01) and the reductions in both variables were similar during CGRP infusion in both groups. Cardiac index (CI) was increased (P < 0.01) in the enflurane group throughout the study while CI increased (P < 0.01) only during infusion in the isoflurane group. Heart rate (HR) remained unchanged (from 135 +/- 6 bpm to 134 +/- 7 bpm) in the enflurane group but tended to increase (from 162 +/- 9 bpm to 171 +/- 9 bpm) in the isoflurane group during infusion. Intergroup differences in HR were found (P < 0.05). Plasma epinephrine concentrations increased (from 42.4 +/- 12.7 pg.ml-1 to 115.3 +/- 41.8 pg.ml-1, P < 0.01) during infusion in the isoflurane group. However, these increases were suppressed (from 46.6 +/- 23.2 pg.ml-1 to 64.7 +/- 32.4 pg.ml-1) to a greater extent in the enflurane group.

CONCLUSION

The haemodynamic responses, except for HR, of CGRP infusion are similar during enflurane and isoflurane anaesthesia. Suppression of tachycardia induced by CGRP is greater with enflurane than with isoflurane. The differences in HR may be due to the roles of catecholamine responses resulting from the anaesthetic-induced sympathetic suppression.

Neuropeptide secretion in exercise

Plasma concentrations of atrial natriuretic peptide immunoreactivity (irANP) and brain natriuretic peptide immunoreactivity (irBNP) in elderly normal subjects (mean age 71.1, range 66-81 years, n = 10) were examined before (rest), during (peak of exercise) and after (3 min, 6 min) a treadmill exercise test (modified Bruce protocol). An attempt was also made to determine the effect of steady state exercise (30% and 50%) and posture (supine, sitting) on circulating levels of atrial natriuretic peptide and calcitonin gene-related peptide (CGRP) in man. The results suggest that exercise gives rise to increased levels of irANP and irCGRP, but not human BNP. The study also demonstrated a >40% rise in irCGRP and irANP levels at 50% steady state exercise compared with 30% steady state exercise. irCGRP was shown to decline in the upright position compared with the supine position, and irCGRP did not rise with exercise. Although ANP is normally stored in large concentration in the atria with much less in the ventricles and BNP is derived to a much greater extent from the ventricles, the differential release rate of these peptides may make BNP concentration a more sensitive indicator of left ventricular dysfunction than ANP. The observations obtained here also raise the possibility that the ANP system may not only help to eliminate intermittent overhydration, but also participate in the postural regulation of diuresis and natriuresis and perhaps even support the maintenance of excretory kidney function in the ageing subjects.

Local neurogenic regulation of rat hindlimb circulation: CO2-induced release of calcitonin gene-related peptide from sensory nerves

1. The mechanism of release of calcitonin gene-related peptide (CGRP) from sensory nerves in response to skeletal muscle contraction was investigated in the rat hindlimb in vivo and in vitro. 2. In the anaesthetized rat, sciatic nerve stimulation at 10 Hz for 1 min caused a hyperaemic response in the hindlimb. During the response, partial pressure of CO2 in the venous blood effluent from the hindlimb significantly increased from 43 +/- 3 to 73 +/- 8 mmHg, whereas a small decrease in pH and no appreciable change in partial pressure of O2 were observed. 3. An intra-arterial bolus injection of NaHCO3 (titrated to pH 7.2 with HCl), which elevated PCO2 of the venous blood, caused a sustained increase in regional blood flow of the iliac artery. Capsaicin (0.33 micromol kg(-1), i.a.) and a specific calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37), (100 nmol kg(-1) min(-1), i.v.) significantly suppressed the hyperaemic response to NaHCO3. Neither ND(omega)-nitro-L-arginine methyl ester (1 micromol kg(-1) min(-1), i.v.) nor indomethacin (5 mg kg(-1), i.v.) affected the response. 4. The serum level of CGRP-like immunoreactivity in the venous blood was significantly increased by a bolus injection of NaHCO3 (pH = 7.2) from 50 +/- 4 to 196 +/- 16 fmol ml(-1). 5. In the isolated hindlimb perfused with Krebs-Ringer solution, a bolus injection of NaHCO3 (pH = 7.2) caused a decrease in perfusion pressure which was composed of two responses, i.e., an initial transient response and a slowly-developing long-lasting one. CGRP(8-37) significantly inhibited the latter response by 73%. 6. These results suggest that CO2 liberated from exercising skeletal muscle activates capsaicin-sensitive perivascular sensory nerves locally, which results in the release of CGRP from their peripheral endings, and then the released peptide causes local vasodilatation.

Mechanism of action of human calcitonin gene-related peptide in rabbit heart and in human mammary arteries

We investigated the effects of human calcitonin gene-related peptide (CGRP) on isolated rabbit hearts to evaluate the mechanisms responsible for the vasodilatory action of the peptide on the coronary district, monitoring contemporaneously the effects on left ventricular pressure (LVP) and heart rate (HR). We also evaluated the reactivity of the human internal mammary artery (IMA) to excitatory drugs acting with different mechanisms and the inhibitory response to CGRP in comparison with the commonly used vasodilatory agents. The peptide induced a slight inhibitory effect on the basal coronary perfusion pressure (CPP), whereas it was ineffective on the inotropism and chronotropism. A more detectable coronary vasodilation was evident when CPP was increased by spasmogenic agents [vasopressin, methoxamine, Bay K 8644, and prostaglandin F2 alpha (PGF2 alpha)]. This inhibitory effect was dose dependent (10(-11)-10(-8) M) and apparently not specific, occurring to the same extent on different stimuli. Forskolin (10(-8) M), an adenylate-cyclase activator, and indomethacin (1.4 x 10(-5) M), a cyclooxygenase inhibitor, did not modify the spasmolytic activity of CGRP on precontracted coronary smooth muscle. The experiments performed on the segments of IMA, used for myocardial revascularization of patients affected by coronary diseases, have shown an evident spasmolytic action of CGRP on increased vascular tone induced by KCl (90 mM), noradrenaline (10(-5) M), serotonin (10(-6) M), and angiotensin II (10(-6) M). These inhibitory responses of CGRP on the spasmogenic compounds disappeared when the endothelial function of IMA, validated by the acetylcholine test, was abolished by mechanical ablation. A series of IMA segments was incubated (30 min) with N(G)-monomethil-L-arginine (L-NMMA), which inhibits nitric oxide (NO) synthase. In these experiments, the peptide failed to induce the vasodilation, suggesting that its action may be related to synthesis of NO. All these results show that CGRP is able to induce a potent vasodilatory action on different vessels of humans (internal mammary artery) and animals (rabbit coronary arteries). In particular the data obtained from IMA demonstrated that the vasorelaxant effect was related to synthesis of NO, one of the most studied endothelium-derived relaxing factors (EDRFs).

Influence of meal composition on postprandial peripheral plasma concentrations of vasoactive peptides in man

In a randomized cross-over study healthy non-obese male human subjects received standardized isocaloric, isovolumetric meals consisting of either carbohydrate, protein or fat and a non-caloric control meal consisting of an equal volume of water. Peripheral venous plasma concentrations of calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and peptide YY (PYY) were measured pre- and postprandially. Plasma CGRP concentrations were lowered following the protein meal and following the fat meal, but remained unaltered after carbohydrate or water ingestion. Plasma VIP concentrations increased slightly following the carbohydrate meal and following water loading. The PYY concentrations increased after the protein and the carbohydrate meal and a slight rise was observed following fat ingestion. Water loading did not affect the plasma level of PYY. We conclude that the postprandial peripheral plasma concentrations of CGRP, VIP and PYY are dependent on the caloric meal composition. The VIP, but not the CGRP and PYY concentrations seem to be influenced by gastric distension. The physiological significance of the postprandial alterations in peripheral concentrations of these peptides is at present uncertain.

Calcitonin gene-related peptide is a potent intestinal, but not gastric, vasodilator in conscious dogs

The effects of human alpha-calcitonin gene-related peptide (alpha-CGRP), beta-CGRP, and vasoactive intestinal polypeptide (VIP) on left gastric (LGA) and superior mesenteric arterial (SMA) blood flow, heart rate and systemic arterial blood pressure were investigated in 6 conscious beagle dogs. Both intravenous injections of alpha-CGRP and beta-CGRP (5-200 pmol/kg) and infusion of alpha-CGRP (25-100 pmol/kg per h) induced a dose-related increase in SMA flow and a dose-related decrease in its resistance. At lower doses, alpha-CGRP was more potent than beta-CGRP, but their maximal responses were the same. alpha-CGRP and beta-CGRP had little effect on LGA flow. However, alpha-CGRP at 200 pmol/kg, but not beta-CGRP, stimulated gastroduodenal contractions that were associated with a phasic increase of LGA flow. Atropine inhibited gastric, but not duodenal, motor and circulatory responses to alpha-CGRP. Tachycardia and hypotension induced by beta-CGRP were significantly less than those by alpha-CGRP. VIP, on the other hand, increased mainly LGA flow. These results suggest that blood vessels of the small intestine of dogs are more sensitive to CGRP than those of the stomach, while the sensitivity to VIP is reversed.