The actions of calcitonin gene related peptide and vasoactive intestinal peptide as vasodilators in man in vivo and in vitro

The effects of CGRP in vascular tissue - Classical vasodilation, shadowed effects and systemic dilemmas

Vascular tissue consists of endothelial cells, vasoactive smooth muscle cells and perivascular nerves. The perivascular sensory neuropeptide CGRP has demonstrated potent vasodilatory effects in any arterial vasculature examined so far, and a local protective CGRP-circuit of sensory nerve terminal CGRP release and smooth muscle cell CGRP action is evident. The significant vasodilatory effect has shadowed multiple other effects of CGRP in the vascular tissue and we therefore thoroughly review vascular actions of CGRP on endothelial cells, vascular smooth muscle cells and perivascular nerve terminals. The actions beyond vasodilation includes neuronal re-uptake and neuromodulation, angiogenic, proliferative and antiproliferative, pro- and anti-inflammatory actions which vary depending on the target cell and anatomical location. In addition to the classical perivascular nerve-smooth muscle CGRP circuit, we review existing evidence for a shadowed endothelial autocrine pathway for CGRP. Finally, we discuss the impact of local and systemic actions of CGRP in vascular regulation and protection from hypertensive and ischemic heart conditions with special focus on therapeutic CGRP agonists and antagonists.

Vampire Venom: Vasodilatory Mechanisms of Vampire Bat (Desmodus rotundus) Blood Feeding

Animals that specialise in blood feeding have particular challenges in obtaining their meal, whereby they impair blood hemostasis by promoting anticoagulation and vasodilation in order to facilitate feeding. These convergent selection pressures have been studied in a number of lineages, ranging from fleas to leeches. However, the vampire bat (Desmondus rotundus) is unstudied in regards to potential vasodilatory mechanisms of their feeding secretions (which are a type of venom). This is despite the intense investigations of their anticoagulant properties which have demonstrated that D. rotundus venom contains strong anticoagulant and proteolytic activities which delay the formation of blood clots and interfere with the blood coagulation cascade. In this study, we identified and tested a compound from D. rotundus venom that is similar in size and amino acid sequence to human calcitonin gene-related peptide (CGRP) which has potent vasodilatory properties. We found that the vampire bat-derived form of CGRP (i.e., vCGRP) selectively caused endothelium-independent relaxation of pre-contracted rat small mesenteric arteries. The vasorelaxant efficacy and potency of vCGRP were similar to that of CGRP, in activating CGRP receptors and Kv channels to relax arteriole smooth muscle, which would facilitate blood meal feeding by promoting continual blood flow. Our results provide, for the first time, a detailed investigation into the identification and function of a vasodilatory peptide found in D. rotundus venom, which provides a basis in understanding the convergent pathways and selectivity of hematophagous venoms. These unique peptides also show excellent drug design and development potential, thus highlighting the social and economic value of venomous animals.

Endosomal proteolysis regulates calcitonin gene-related peptide responses in mesenteric arteries

BACKGROUND AND PURPOSE

Calcitonin gene-related peptide (CGRP) is a potent vasodilator, implicated in the pathogenesis of migraine. CGRP activates a receptor complex comprising, calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1). In vitro studies indicate recycling of CLR●RAMP1 is regulated by degradation of CGRP in early endosomes by endothelin-converting enzyme-1 (ECE-1). However, it is not known if ECE-1 regulates the resensitization of CGRP-induced responses in functional arterial tissue.

EXPERIMENTAL APPROACH

CLR, ECE-1a-d and RAMP1 expression in rat mesenteric artery smooth muscle cells (RMA-SMCs) and mesenteric arteries was analysed by RT-PCR and by immunofluorescence and confocal microscopy. CGRP-induced signalling in cells was examined by measuring cAMP production and ERK activation. CGRP-induced relaxation of arteries was measured by isometric wire myography. ECE-1 was inhibited using the specific inhibitor, SM-19712.

KEY RESULTS

RMA-SMCs and arteries contained mRNA for CLR, ECE-1a-d and RAMP1. ECE-1 was present in early endosomes of RMA-SMCs and in the smooth muscle layer of arteries. CGRP induced endothelium-independent relaxation of arteries. ECE-1 inhibition had no effect on initial CGRP-induced responses but reduced cAMP generation in RMA-SMCs and vasodilation in mesenteric arteries responses to subsequent CGRP challenges.

CONCLUSIONS AND IMPLICATIONS

ECE-1 regulated the resensitization of responses to CGRP in RMA-SMCs and mesenteric arteries. CGRP-induced relaxation did not involve endothelium-derived pathways. This is the first report of ECE-1 regulating CGRP responses in SMCs and arteries. ECE-1 inhibitors may attenuate an important vasodilatory pathway, implicated in primary headaches and may represent a new therapeutic approach for the treatment of migraine.

Vasoactive intestinal polypeptide relaxes isolated rat pulmonary artery rings through two distinct mechanisms

Vasoactive intestinal polypeptide (VIP), an endogenous neuropeptide normally present in lungs and other organs, relaxes pulmonary arteries (PAs) in different species, whereas the underlying mechanisms are still not fully understood. The aim of this study, therefore, is to investigate the signal transduction of VIP in the relaxation of isolated rat PA rings. The isometric tension of the rings was studied in vitro with force-electricity transducers. In endothelium-intact (EI) rings, VIP elicited concentration-dependent relaxation after the rings were pre-contracted by phenylephrine. A similar effect, though smaller, was observed in endothelium-denuded (ED) rings. Inhibition of the endothelial nitric oxide synthase (eNOS) by NG-nitro-L-arginine methyl ester diminished the VIP-induced vasodilatation of PA rings. The VIP-induced vasorelaxation was markedly reduced by the inhibition of the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway with wortmannin and LY294002, respectively, which was seen in EI rings, but not in ED rings. Western blot analysis revealed that VIP increased the phosphorylation of eNOS at Ser 1177, but did not affect the overall expression of eNOS. In ED rings, the PKA inhibitor H-89 and K(ATP) channel inhibitor glibenclamide almost totally abolished the vasodilatation effect of VIP. The results suggested that the vasodilatation effect of VIP on rat PAs is mediated by both vascular endothelium and smooth muscle, involving respectively the PI3K/Akt-eNOS pathway and the PKA-K(ATP) channel pathway.

Involvement of endothelial NO in the dilator effect of VIP on rat isolated pulmonary artery

The endothelium and its interaction with smooth muscle play a central role in the local control of the pulmonary vasculature, and endothelial dysfunction is thought to contribute to pulmonary hypertension and chronic obstructive pulmonary disease. Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, relaxes the rat pulmonary artery, but there is controversy as to whether or not this action of VIP depends on the endothelium. The aim of this study, therefore, was to investigate the role of the endothelium and nitric oxide (NO), the major endothelium-derived relaxing factor, in the dilator action of VIP on the rat isolated pulmonary artery. Pulmonary artery preparations pre-contracted by the alpha(1)-adrenoceptor agonist L-phenylephrine were relaxed by VIP (0.003-1 microM) and acetylcholine (0.003-10 microM) in a concentration-dependent manner. Mechanical removal of the endothelium reduced the maximal response to VIP by about 50% and practically abolished the response to acetylcholine. Inhibition of NO synthesis by N(omega)-nitro-L-arginine methyl ester (0.5 mM) had a similar effect, abolishing the vasorelaxation caused by acetylcholine and attenuating the vasorelaxation caused by VIP by about 50%. From these data it is concluded that the relaxant action of VIP on the rat isolated pulmonary artery depends in part on the presence of the endothelium and that this part is mediated by endothelial NO.

Human VIP-alpha: an emerging biologic response modifier to treat primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare life-threatening disorder of unknown etiology manifested by chronic elevation of pulmonary arterial pressure. Given that pulmonary vasoconstriction, endothelial and vascular smooth muscle cell proliferation and in situ thrombosis contribute appreciably to the evolution of PPH, treatment with vasodilators, antiproliferative drugs and anticoagulants, alone or in combination, constitute the pharmacologic standard of care. To this end, long-term administration of oral calcium channel blockers, prostacyclin analogs by various routes and oral endothelin-1 receptor antagonists, alone or in combination, is efficacious in treating patients with PPH. Unfortunately, efficacy is hampered by poor stability, delivery and bioavailability, and by systemic toxicity. Hence, there is an ongoing need to develop and test new drugs to treat patients with PPH. To address this issue, a novel, targeted, long-acting, biocompatible and safe sterically stabilized liposomal and micellar formulation of human vasoactive intestinal peptide (VIP) was developed and tested for human use: the 28-amino acid pleiotropic biologic response modifier, human VIP-alpha. The long-lasting salutary effects of phospholipid-associated VIP on vasomotor tone and arterial pressure were expressed at low concentrations solely in diseased animals and were independent of its route of administration. Thus, the author proposes that human VIP-alpha could be developed as a safe long-acting drug to treat patients with PPH.

Reproducibility of forearm vasodilator response to intra-arterial infusion of calcitonin gene-related peptide assessed by venous occlusion plethysmography

AIMS

To assess the reproducibility of the forearm blood flow (FBF) response to intra-arterial infusion of calcitonin-gene related peptide (CGRP), measured by venous occlusion plethysmography. In addition, to compare different ways of expressing the FBF response and perform sample size calculations.

METHODS

On two separate visits, CGRP (10 ng min(-1) dl(-1) forearm) was infused for 45 min into the brachial artery of six healthy subjects. Reproducibility was assessed by calculating mean difference, repeatability coefficient, within-subject coefficient of variation (WCV) and intraclass correlation coefficient.

RESULTS

CGRP increased FBF from 2.8 +/- 0.4 and 3.2 +/- 0.7 (at baseline) to 15.4 +/- 1.4 and 15.2 +/- 1.5 ml min(-1) dl(-1) forearm (at 45 min) on visits 1 and 2, respectively (P < 0.0001 for both visits). Mean difference in FBF at 45 min between both visits was 0.3 ml min(-1) dl(-1) forearm (repeatability coefficient: 4.1 ml min(-1) dl(-1) forearm). This FBF response appeared to be more reproducible when expressed as absolute FBF in the infused arm (WCV 11%) compared with absolute FBF-ratio between both arms (WCV 37%), percentage change from baseline in FBF in the infused arm (WCV 29%) and percentage change from baseline in FBF-ratio (WCV 40%). When expressed as absolute FBF, a sample size of five (95% confidence interval: 2-12) subjects gives 90% power at a type I error probability of 0.05 to detect a 25% shift in FBF response.

CONCLUSIONS

Intra-arterial infusion of CGRP results in a forearm vasodilator response which is reproducible between days. This response is most reproducible when expressed as absolute FBF. The presented methodology provides a suitable pharmacodynamic model to assess the in vivo activity of CGRP-receptor antagonists in a small number of subjects.

Expression and secretion of procalcitonin and calcitonin gene-related peptide by adherent monocytes and by macrophage-activated adipocytes

OBJECTIVE

To explore the roles of peripheral blood mononuclear cells (PBMCs) and PBMC-derived macrophages in sepsis-related increased procalcitonin and calcitonin gene-related peptide (CGRP) I production.

DESIGN

Prospective, in vitro primary human cell culture study and human tissue samples gene expression analysis.

SETTING

University hospital research laboratories.

PATIENTS

Cells from healthy donors and septic patients.

INTERVENTIONS

PBMCs were obtained from healthy donors. Isolation of pure monocyte cultures was performed by magnetic depletion of nonmonocyte cells from PBMCs. Adipose tissue biopsies and circulating leukocytes were collected from septic patients. Expressions of calcitonin messenger RNA and CGRP I messenger RNA were analyzed using reverse transcriptase-polymerase chain reaction and quantitative real-time polymerase chain reaction. Supernatant procalcitonin and CGRP protein content were determined by ultrasensitive chemiluminometric and radioimmunoassays, respectively.

MEASUREMENTS AND MAIN RESULTS

PBMCs expressed and secreted procalcitonin and CGRP within 3-5 hrs after adherence to endothelial cells or plastic surfaces. This induction was transient, as it was not detectable after 18 hrs. No calcitonin or CGRP I messenger RNA was observed in leukocytes obtained from septic patients with markedly increased serum procalcitonin concentrations. Stimulation with cytokines, endotoxin, or Escherichia coli did not induce expression of calcitonin and CGRP I messenger RNA in PBMC-derived macrophages. However, inflammatory factors released from activated macrophages induced a marked expression of procalcitonin and CGRP in co-cultured human adipocytes.

CONCLUSIONS

The adhesion-induced, transient expression and secretion of procalcitonin and CGRP in vitro may play an important role during monocyte adhesion and migration in vivo. PBMC-derived macrophages may contribute to the marked increase in circulating procalcitonin by recruiting parenchymal cells within the infected tissue, as exemplified with adipocytes.

Vasorelaxations induced by calcitonin gene-related peptide, vasoactive intestinal peptide, and acetylcholine in aortic rings of endothelial and inducible nitric oxide synthase-knockout mice

The objective of this study was to determine if vasorelaxant responses to calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP), and acetylcholine are altered in aortic rings of mice lacking genetic expression of endothelial nitric oxide synthase (eNOS) or inducible nitric oxide synthase (iNOS) genes (i.e., eNOS- and iNOS-knockout mice) as compared with control (wild-type) mice. Aortic rings from eNOS-knockout (eNOS (-/-)) mice did not relax in response to acetylcholine, thereby confirming previous reports. Aortic rings from iNOS-knockout (iNOS (-/-)) mice relaxed in response to acetylcholine in an endothelium-dependent manner. However, maximum relaxations in endothelium-intact rings were significantly (p < 0.05) larger than in control mice (85.3 +/- 3.1% in iNOS (-/-) mice vs. 67.9 +/- 5.6% in controls). CGRP caused concentration-dependent relaxations in aortas of all three types of mice: control mice, iNOS (-/-) mice, and eNOS (-/-) mice. Vasorelaxant responses to CGRP in control and iNOS (-/-) mice had identical relationships; both were partially dependent on endothelium. In eNOS (-/-) mice, dose-response curves of CGRP in endothelium-intact and endothelium-denuded rings were not significantly different, indicating loss of the partial dependence on endothelium. The vasorelaxant responses to VIP were completely dependent on endothelium in control and iNOS (-/-) mice. Maximum relaxations to VIP in iNOS (-/-) mice (77.4 +/- 2.7%) were significantly greater than in control mice (64.0 +/- 5.5%). Vasorelaxant responses to VIP in eNOS (-/-) aortic rings were also endothelium-dependent, but responses were greatly attenuated compared with wild-type mice. Relaxations induced by VIP (1 x 10 ) in endothelium-intact aortic rings of eNOS (-/-) mice and control mice were 18.3 +/- 5.4% and 64.0 +/- 5.5%, respectively. These findings demonstrated that, in eNOS (-/-) mice, aortic vasorelaxant responses to CGRP were fully present but no longer dependent on the endothelium, and responses to VIP were greatly attenuated compared with control and responses to acetylcholine were abolished. In iNOS (-/-) mice, aortic vasorelaxant responses to VIP and acetylcholine were significantly greater than wild-type control, suggesting that induction of iNOS may have attenuated vascular responses to VIP and acetylcholine in wild-type controls.

Cardiovascular pharmacology of anandamide

The fatty acid amide anandamide produces hypotension and a decrease in systemic vascular resistance in vivo. A drop in blood pressure is also seen with synthetic cannabinoid (CB) receptor agonists. The hypotensive responses to anandamide and synthetic cannabinoids are absent in CB1 receptor gene knockout mice. In isolated arteries and perfused vascular beds, anandamide induces vasodilator responses, which cannot be mimicked by synthetic cannabinoids. Instead, vanilloid receptors on perivascular sensory nerves play a key role in these effects of anandamide. Activation of vanilloid receptors by anandamide triggers the release of sensory neuropeptides such as the vasodilator calcitonin gene-related peptide (CGRP). Anandamide is detected in blood and in many cells of the cardiovascular system, and macrophage-derived anandamide may be involved in several hypotensive clinical conditions. Interestingly, cannabinoid and vanilloid receptors display an overlap in ligand recognition properties, and the frequently used CB1 receptor antagonist SR141716A also inhibits vanilloid receptor-mediated responses. The presence of anandamide in endothelial cells, neurones and activated macrophages (monocytes), and its ability to activate CB and vanilloid receptors make this lipid a potential bioregulator in the cardiovascular system.

Severe impairment of CGRP-induced hypotension in vivo and vasorelaxation in vitro in elderly rats

The aim of this study was to investigate the effects of aging on hypotension in vivo and vasorelaxation in vitro induced by calcitonin gene-related peptide (CGRP), using young (3 months old) and elderly (20 and 28 months old) Sprague-Dawley rats. Vasorelaxant responses were measured in isolated rings of rat thoracic aorta and rat caudal artery, which show endothelium-dependent and endothelium-independent responses to CGRP, respectively. The CGRP-induced vasorelaxations were significantly diminished in 28-month-old male rats in both aorta (39.3% of responses in young controls at 10 nM CGRP) and caudal artery (28.5% of responses in young controls at 10 nM CGRP). Acetylcholine caused vasorelaxations in aortic rings of young male rats, but vasocontractions in aortic rings of 28-month-old male rats. Hypotension induced by CGRP was significantly diminished in both 20-month-old male rats (47.7% of young controls) and 20-month-old female rats (34.4% of young controls). Moreover, ovariectomy, known to decrease CGRP-induced hypotension in young female rats, did not further decrease hypotension to CGRP in elderly female rats. In conclusion, vasorelaxant responses in vitro and hypotensive responses in vivo induced by the neuropeptide CGRP are severely impaired in elderly rats as compared to young rats. The data suggest that the vasodilatory responses to CGRP in both large arteries and the small resistance-sized arteries regulating arterial blood pressure are damaged or down-regulated by the aging process.

Vasorelaxant response to isoprenaline, nitric oxide donor, calcitonin gene-related peptide and vasoactive intestinal peptide in aortic rings of adult C57BL/6J mice

The mouse and tissues from this species are increasingly used as experimental models because of the wide variety of gene deletions and overexpressions available in this species. Yet, very little is known about normal vascular responses in the mouse. We investigated the vasorelaxant responses on thoracic aortic rings from the adult male C57BL/6J mouse. Isoprenaline, acetylcholine, calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and sodium nitroprusside all caused concentration-dependent relaxations in aortic rings possessing healthy endothelium and precontracted with phenylephrine. Maximum relaxations were 64.9+/-2.6%, 66.8+/-2.9%, 114.3+/-4.6%, 65.1+/-4.2% and 116.2+/-5.1% with -logEC(50) values of 6.76+/-0.14, 7.04+/-0.11, 8.53+/-0.14, 8.29+/-0.26 and 8.10+/-0.20 for isoprenaline, acetylcholine, CGRP, VIP and sodium nitroprusside, respectively. There were significantly smaller responses to isoprenaline, acetylcholine, CGRP and VIP when the endothelium was denuded. The maximum relaxations for isoprenaline, CGRP and acetylcholine were 48.3+/-5.1%, 99.6+/-4.4% and 5.7+/-1.6% with -logEC(50) values of 6.44+/-0.40 and 8.23+/-0.192, respectively, following endothelium removal. The response to VIP was completely dependent to endothelium. Without precontraction, isoprenaline, at the higher doses, caused small contractions. These experiments provide new information about vascular responses of five vasodilators in aortic rings of adult male C57BL/6J mice.

Acute ischemic chest pain is not associated with increased calcitonin gene-related peptide (CGRP) levels in peripheral plasma nor in the coronary circulation

Calcitonin gene-related peptide (CGRP) and substance P co-exist in capsaicin-sensitive primary sensory neurons and are released from the myocardium after activation of sensory nerve fibres as well as by ischemia in animals. This study was undertaken to try to clarify the potential involvement of immunoreactive (ir) CGRP in anginal pain and myocardial ischemia in humans. One clinical group (n = 87) and one experimental group (n = 14) were studied. The clinical group was admitted to a coronary care unit with suspected or definite acute myocardial infarction (AMI). The experimental group consisted of patients with severe angina pectoris (NYHA III-IV). This group was subjected to atrial pacing up to the appearance of angina pectoris. Mean irCGRP levels at admission for the clinical group with and without AMI showed no significant difference. Neither were any significant differences found in irCGRP concentrations between patients with pain as compared to those without pain or in the group who had had chest pain >30 min before hospital admission as compared to those with chest pain <30 min. Extraction ratios for lactate and irCGRP was calculated in the experimental group. No statistically significant covariance was found between irCGRP extraction ratio and lactate extraction ratio (r(xy) = -0.006) at the time of appearance of angina during atrial pacing. Despite the facts that CGRP may be liberated by a variety of physiological stimuli and may act as a potent vasodilator in the human vasculature, no evidence has been found in this study that CGRP release is increased as a consequence of ischemia or ischemic pain.

Nitric oxide donors enhance calcitonin gene-related peptide-induced elevations of cyclic AMP in vascular smooth muscle cells

Vasorelaxant effects of calcitonin gene-related peptide (CGRP) are dependent on endothelium-derived nitric oxide (NO) in some arteries. The mechanism involved is still not clear. In the present study, we used NO donors (sodium nitroprusside (SNP) and 6-(2-hydroxy-1-methyl-2-nitrisohydrazino)-N-methyl-1-hyxanamine (NOC-9)), cyclic GMP elevator (brain natriuretic peptide (BNP)) and a selective type III (cyclic GMP-inhibited) phosphodiesterase (PDE) inhibitor 5-(4-acetamidophenyl)pyrazin-2(1H)-one (SK&F94120) to investigate involvement of NO, cyclic GMP and type III PDE in CGRP-induced accumulation of cyclic AMP in cultured rat aortic smooth muscle cells. SNP (10 microM), NOC-9 (10 microM) and BNP (1 microM) all increased intracellular cyclic GMP to similar levels (2- to 2.5-fold above basal) and caused significant enhancement of CGRP (10 nM)-induced cyclic AMP accumulation similar to that caused by 10 microM SK&F 94120. The data are therefore consistent with our hypothesis that the mechanism of endothelium-dependent vasorelaxation effect of CGRP involves cyclic GMP-mediated inhibition of type III PDE and subsequent accumulation of cyclic AMP in smooth muscle cells.

Brain natriuretic peptide enhances the endothelium-independent cAMP and vasorelaxant responses of calcitonin gene-related peptide in rat aorta

Calcitonin gene-related peptide (CGRP) causes vasorelaxation in rat aorta involving endothelium/nitric oxide (NO)-dependent elevations of both cAMP and cGMP levels. When endothelium is removed, preincubation with exogenous NO uncovers and potentiates direct (endothelium-independent) cAMP elevations and vasorelaxations caused by CGRP. This enhancing effect of NO potentially involves elevation of cGMP and inhibition of Type III (cGMP-inhibitable) phosphodiesterase, causing accumulation of cAMP. However, NO may have other actions. The aim of the present study was to determine if brain natriuretic peptide (BNP), which elevates cGMP levels independent of NO, could enhance cAMP accumulations and vasorelaxations induced by CGRP in rat aortic rings denuded of endothelium. When added separately, neither CGRP (100 nM) nor BNP (10 nM) altered cAMP levels. When added in combination, CGRP (100 nM) and BNP (10 nM) significantly elevated cAMP levels (from control of 0.95+/-0.08 to 1.53+/-0.09 pmol/mg protein) at 2 min. BNP (10 nM) elevated cGMP levels 10-fold at 2 min and this response was not altered by co-administration of CGRP (100 nM). Pretreatment with BNP at concentrations as low as 1 nM in endothelium-denuded aortic rings greatly enhanced the direct vasorelaxant effects of CGRP (100 nM) (from control of 0% to 57.6+/-6.8% relaxation of phenylephrine-precontractions). Our findings indicate that BNP enhances direct (endothelium-independent) cAMP elevations and vasorelaxations caused by CGRP in rat aorta, thus supporting the concept that cGMP inhibits cAMP metabolism and enhances CGRP-induced responses in aortic smooth muscle cells.

Mouse aorta: a preparation highly sensitive to the vasodilatory action of CGRP

Calcitonin gene-related peptide (CGRP), carbamylcholine, and vasoactive intestinal peptide (VIP) caused a concentration-related relaxation in mouse aorta precontracted to noradrenaline. Maximal relaxations obtained were 110, 44, and 46% with median effective concentrations (EC50) values of 7.8, 813.7, and 24.5 nM for CGRP, carbamylcholine, and VIP, respectively. The carbamylcholine- and VIP-induced relaxations were exclusively mediated by endothelial cell-derived factors, whereas CGRP maintained a full vasodilatory action in denuded aorta. However, its concentration-response curve was slightly shifted to the right in the absence of endothelium. The relaxation caused by CGRP was also slightly inhibited at 2 x 10(-8) M by removal of endothelium and in the presence of methylene blue, NG-nitro-L-arginine methylester (L-NAME), or glibenclamide but was not affected by atropine, propranolol, indomethacin, or tetrodotoxin. Moreover, the absence of Ca2+ in the bathing solution had no inhibitory effect on CGRP-induced relaxation in noradrenaline-precontracted aorta. It is concluded that the relaxation evoked by CGRP in the mouse aorta does not mainly depend on an endothelium-derived factor or on the activation of ATP-sensitive K+ (KATP) channels but rather is caused by a mechanism primarily associated with the inhibition of the mobilization of intracellular Ca2+.

Effects of adrenomedullin and calcitonin gene-related peptide on airway and pulmonary vascular smooth muscle in guinea-pigs

1. The airway and pulmonary vascular effects of adrenomedullin were studied in the guinea-pig isolated trachea, main bronchi and pulmonary artery in vitro and compared to the effects of calcitonin gene-related peptide (CGRP). 2. In tracheal rings, CGRP (1 nM to 1 microM) potentiated the cholinergic contractions induced by electrical field stimulation (EFS) at 5 Hz in a concentration-dependent manner. At a concentration of 1 microM, CGRP slightly decreased the responses to log EFS frequency, producing 50% of the maximum contraction from a control value of 0.77 +/- 0.10 Hz to 0.54 +/- 0.05 Hz without a significant effect on the concentration-response curves to acetylcholine (ACh). In contrast, adrenomedullin (1 nM to 1 microM) did not alter either EFS-induced cholinergic or ACh-induced contractions. 3. In bronchial strips, CGRP (1 nM to 1 microM) slightly reduced both the non-adrenergic non-cholinergic (NANC) contraction induced by EFS at 10 Hz and the substance P (1 microM)-induced contraction in a concentration-dependent manner, whereas adrenomedullin (1 nM to 1 microM) was without effect. 4. Neither CGRP (1 microM) nor adrenomedullin (1 microM) altered NANC relaxation induced by EFS at 5 Hz in tracheal rings precontracted with histamine (10 microM). 5. Adrenomedullin (1 nM to 1 microM) and CGRP (1 nM to 1 microM) induced a concentration-dependent relaxation of the histamine (10 microM)- and prostaglandin F2 alpha (10 microM)-precontracted pulmonary arterial rings with intact endothelium with a similar potency. 6. Neither removal of the endothelium nor NG-nitro-L-arginine methyl ester (100 microM) altered the vasorelaxant effects of adrenomedullin (1 nM to 1 microM) and CGRP (1 nM to 1 microM). 7. The putative CGRP receptor antagonist, CGRP8-37 (1 microM to 10 microM) concentration-dependently attenuated the CGRP (3 nM to 30 nM)-induced vasorelaxant actions, whereas it had no effect on the relaxation of vessel rings induced by adrenomedullin (3 nM to 30 nM). 8. These results suggest that adrenomedullin is a potent vasodilator of the pulmonary artery without any bronchomotor effect in the guinea-pig lung, and that the vasorelaxant actions of adrenomedullin are not mediated via the activation of CGRP1 receptors.

Effect of parasympathetic and sensory transmitters on human epicardial coronary arteries and veins

Vasomotor effects of various agonists were tested on isolated human epicardial coronary arteries and veins at resting tension and after precontraction with U46619. Acetylcholine relaxed all arteries with intact endothelium but only some endothelium-denuded arteries. Most veins did not relax to acetylcholine. Higher concentrations of acetylcholine induced powerful contractions of all arteries and veins. Preincubation with atropine significantly lowered the pD(2) values but not E(max) values for contractile responses to acetylcholine in arteries and veins (pA(2) value for atropine 9.1 arteries and 9.6 veins). Vasoactive intestinal peptide, human alpha-calcitonin gene-related peptide and substance P potently relaxed all arteries with intact endothelium and all veins. Removal of the arterial endothelium abolished relaxation to substance P in most arteries whereas responses to vasoactive intestinal peptide were unaffected, and for alpha-calcitonin gene-related peptide the pD(2) value but not the E(max) value was significantly lowered. In both arteries and veins, the antagonists alpha-calcitonin gene-related peptide (8-37) and spantide lowered significantly the potency for alpha-calcitonin gene-related peptide and substance P, respectively, without significant changes in E(max) values (pA(2) value for alpha-calcitonin gene-related peptide (8-37) 7.9 arteries and 7.9 veins, for spantide 7.6 arteries and 8.1 veins).

Mediators, cytokines, and growth factors in liver-lung interactions

Multiple mediators have been implicated in the interactions between the liver and the lungs in various disease states. The best characterized mediator of liver-lung interaction is alpha 1-antitrypsin. Several cytokines and mediators may be involved in the pathogenesis of the hepatopulmonary syndrome and in the cytokine cascades that are activated in systemic inflammatory states such as acute respiratory distress syndrome. Hepatocyte growth factor or scatter factor is a recently described peptide with a broad range of biologic effects that may mediate lung-liver interactions.

CGRP innervation and receptors during aging of male and female hepatic rat portal veins

Calcitonin gene-related peptide (CGRP) innervation and binding sites were studied on hepatic portal veins of male and female rats from 19 days to 22 months of age. CGRP containing nerve fibers were present both in adventitial and medial nerve plexuses, closely apposing to or penetrating into the muscular layers. The density of CGRP innervation was estimated on whole mount preparations and compared during aging. In females, aging did not affect the number of fibers per unit length, although the vessel circumference decreased after 6 months of age. In males, the vessel circumference remained constant during aging, while the density of innervation significantly decreased. Whatever the age or sex of the animals was, no CGRP binding sites were found on portal veins sections by autoradiography. CGRP had no effect on spontaneous contractions of perfused portal veins. The difference observed in the evolution of CGRP innervation density between males and females suggests that CGRP innervation in the rat portal vein may be influenced by gonadal steroids during aging.

Diverse interactions of calcitonin gene related peptide and nitric oxide in the gastric and cutaneous microcirculation

Calcitonin gene related peptide (CGRP) is the major mediator of afferent nerve mediated vasodilatation in the gastric mucosa and skin of the rat. Since receptors for CGRP occur on both the vascular endothelium and smooth muscle, it is conceivable that the vascular actions of CGRP involve multiple mechanisms. The vasodilator effect of rat CGRP-alpha in the rat gastric mucosa is indeed inhibited by blockage of nitric oxide (NO) synthesis, as is the gastric mucosal hyperemia in response to gastric acid challenge, which is mediated by CGRP release from afferent nerve fibres. In contrast, the vasodilator response to rat CGRP-alpha in the rat hind paw and the CGRP-mediated vasodilatation evoked by antidromic stimulation of afferent nerve fibres do not depend on the formation of NO. These data indicate that NO plays regionally different roles in the local vasodilator action of CGRP. NO is a secondary vasorelaxant messenger of CGRP in the gastric, but not in the cutaneous, microcirculation. However, this L-arginine-derived autacoid may have a role in the irritant-induced CGRP release from afferent vasodilator fibres in the skin.

Endothelium-dependent vasodilation of peripheral conduit arteries in patients with heart failure

Endothelium-dependent vasodilation of peripheral resistance vessels is abnormal in patients with heart failure, but there are little in vivo data on endothelium-dependent vasodilation of peripheral conduit vessels. This study assessed endothelium-dependent vasodilation of forearm conduit and resistance vessels in normal subjects and patients with heart failure. The effects of intraarterial endothelium-dependent and endothelium-independent vasodilators on both forearm conduit (brachial artery) and resistance vessels were assessed in 9 patients with New York Heart Association class II-III heart failure and 11 normal subjects of similar age. Brachial artery diameter was measured by two-dimensional, moderate-frequency (8 MHz) ultrasound, and forearm blood flow was measured by strain gauge plethysmography. The endothelium-dependent vasodilator, methacholine (0.3 and 1.5 micrograms/min), increased brachial artery diameter by 7.6 +/- 1.3% and 12.2 +/- 1.5% in normal subjects as compared to 6.9 +/- 2.1% and 10.4 +/- 2.4% in patients with heart failure (P = NS, normal vs heart failure). The endothelium-independent vasodilator, nitroglycerin (0.15 microgram), also produced similar increases in brachial artery diameter in the two groups (8.2 +/- 1.3% in normal subjects vs 11.1 +/- 1.4% in patients with heart failure, P = NS). In contrast, forearm blood flow responses to methacholine were significantly (P < .05) greater in normal subjects (4.1 +/- 0.5 and 9.2 +/- 1.4 mL/min/100 mL forearm volume) than in patients with heart failure (2.0 +/- 0.8 and 5.1 +/- 1.3 mL/min/100 mL forearm volume). Forearm blood flow responses to the endothelium-independent vasodilator, sodium nitroprusside, were similar between the two groups. This study suggests that endothelium-dependent and endothelium-independent vasodilation of the brachial artery is not impaired in patients with class II-III heart failure. This finding contrasts with abnormal endothelium-dependent vasodilation of forearm resistance vessels. These data suggest that there are regional differences in endothelial function in patients with heart failure.

Skeletal muscle microcirculatory response to rat alpha-calcitonin gene-related peptide

We used in vivo video microscopy to determine the effect of increasing doses of rat alpha-calcitonin gene-related peptide (rCGRP) on rat cremaster muscle arterioles in the presence or absence of the nitric oxide synthase inhibitor N-omega-nitro-L-arginine (L-NNA). Male Sprague-Dawley rats (118-148 g) were anaesthetized with pentobarbital, and neurovascularly intact cremaster muscles were imaged. Changes in the diameter, erythrocyte velocity and volume flow in second-(A2), third-(A3), and fourth-(A4) order arterioles were determined. To produce uniform arteriolar tone, the cremaster preparation was challenged with norepinephrine (NE: 10(-7) M). L-NNA (10(-4) M), which was shown to inhibit acetylcholine-(ACh: 10(-6) M) induced arteriolar dilations, was added to 16 of the preparations. Preparations were then challenged by adding cumulative log concentrations of rCGRP (10(-12)-10-7) M; n = 16) or an equivalent volume of vehicle (n = 19) to the bath. Following rCGRP challenge, arterioles were maximally dilated with 10(-5) M nitroprusside (NP). rCGRP caused significant dose-dependent increases in erythrocyte velocity and volume flow in A2 arterioles, and in diameter, velocity, and volume flow in A3 and A4 arterioles, by 10(-8) M, when compared with vehicle-treated controls. L-NNA had no significant effect on rCGRP-induced responses. These data indicate that rCGRP causes dose-dependent dilation of skeletal muscle resistance arterioles at a concentration similar to that observed in larger vessels. This dilation does not appear to be dependent on the vascular production of nitric oxide from L-arginine.

N omega-nitro-L-arginine inhibits vasodilations and elevations of both cyclic AMP and cyclic GMP levels in rat aorta induced by calcitonin gene-related peptide (CGRP)

Our previous studies showed that vasodilations and elevations of both cyclic AMP and cyclic GMP levels in rat aorta induced by rat calcitonin gene-related peptide (rCGRP) are inhibited by hemoglobin and methylene blue, blockers of the endothelium-derived relaxant factor (EDRF, now recognized as nitric oxide [NO]). In the present study, we used N omega-nitro-L-arginine (L-NNA), a selective inhibitor of nitric oxide synthase, to test whether rCGRP-induced relaxations and cyclic AMP and cyclic GMP responses in rat aorta require de novo synthesis of NO. L-NNA (30 microM, 15 min) inhibited by 84, 76 and 73% the relaxations induced by rCGRP at 1, 10 and 100 nM, respectively. D-NNA (30 microM), which does not inhibit nitric oxide synthase, did not block rCGRP-induced vasorelaxations. Addition of L-arginine (3 mM) 5 min before L-NNA completely prevented the L-NNA-inhibition of CGRP-induced relaxations. L-NNA (30 microM, 15 min) also inhibited the elevations of both cyclic AMP and cyclic GMP levels caused by CGRP (100 nM). The data suggest that de novo synthesis of nitric oxide from its precursor L-arginine is required for rCGRP to induce vasodilations and elevations of both cyclic AMP and cyclic GMP levels in rat aorta.

Effect of calcitonin gene-related peptide on coronary microvessels and its role in acute myocardial ischemia

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a potent dilator of epicardial conduit vessels and is released during myocardial ischemia in humans. However, the effect of CGRP on coronary arterial microvessels is still unclear, and it is unknown if CGRP modulates the tone of coronary arterial microvessels during acute myocardial ischemia.

METHODS AND RESULTS

Epimyocardial microvessels were observed through a microscope equipped with a floating objective system in anesthetized open-chest dogs. Heart rate and aortic pressure were maintained at control levels. Flow velocity of the left anterior descending coronary artery (LAD) was measured with a suction-cup Doppler probe. When CGRP was cumulatively infused into the LAD (0.05, 0.5, 5.0, and 50 pmol/kg per minute) or superfused (0.03, 0.3, 3.0, and 30 nmol/L) over the left ventricular surface, arterial control microvessels > 100 microns in diameter dilated dose dependently at dosages of 0.5 to 50 pmol/kg per minute (infused) or 0.3 to 30 nmol/L (superfused), but those < 100 microns dilated only at the highest dose, and those > 100 microns had greater dilation in both groups. Only the highest dose of CGRP (infused) significantly increased coronary flow. The superfusion of CGRP(8-37) (CGRP receptor antagonist, 300 nmol/L) did not affect the control diameters of coronary arterial microvessels but completely abolished CGRP-induced vasodilation at the same doses (infused and superfused). However, 300 nmol/L of CGRP(8-37) did not affect the response of coronary arterial microvessels to the LAD occlusion in any size.

CONCLUSIONS

CGRP preferentially dilates the coronary arterial microvessels > 100 microns in diameter but has only a small effect on those < 100 microns. Endogenous CGRP does not modulate the tone of coronary arterial microvessels during acute myocardial ischemia in beating canine hearts.

Calcitonin gene-related peptide in treatment of severe peripheral vascular insufficiency in Raynaud's phenomenon

Calcitonin gene-related peptide (CGRP) is a potent vasodilator that may be involved in the regulation of the peripheral circulation and in its response to cold. There is evidence that CGRP in digital cutaneous perivascular nerves is deficient in Raynaud's phenomenon. Our pilot study of intravenous CGRP suggested that this substance is beneficial in patients with Raynaud's phenomenon; here we have extended our studies. Ten patients with severe Raynaud's phenomenon secondary to connective tissue disease were randomly assigned to groups receiving intravenous CGRP (0.6 micrograms/min for 3 h per day on 5 days) or saline. Hand and digital blood flow and skin temperature were measured by thermocouple and laser doppler flowmetry. Blood flow was significantly (p < 0.05) increased by CGRP in both hands (median blood flow after infusion as percentage of baseline reading 179 [range 100-355]%) and fingers (149 [100-161]%); saline had no effect (hands 102 [84-123]%, fingers 96 [81-113]%). Hand temperature was increased more by CGRP than by saline (2.8 [1.5-4.0] vs 1.0 [-1.0 to 2.5] degrees C, p < 0.05). Digital temperature increased after CGRP but the difference between the treatment groups in temperature rise was not significant, perhaps because saline caused increases in some patients. All ulcers healed in four of five CGRP-treated patients but in no saline-treated patients. Thus intravenous CGRP effectively dilates the compromised digital cutaneous vasculature in severe Raynaud's phenomenon.

Capsaicin induced afferent denervation and receptor-linked responses to CGRP in the rat

We have examined the effect of neonatal capsaicin-induced destruction of primary afferent nerves in rats on the response to calcitonin gene-related peptide (CGRP) in vitro and in vivo. Denervation was confirmed by immunohistochemistry. Rat alpha-CGRP (rCGRP) activated adenylate cyclase in homogenates of rat spleen (basal activity 45 +/- 8.27, delta Vmax 75 +/- 16 pmol cyclic AMP min-1 protein; K(act) 2.04 +/- 0.44 nM). A single specific binding site for [125I]hCGRP was demonstrated in homogenates of spleen (Kd = 4.84 +/- 0.66 nM, Bmax = 1.43 +/- 0.35 pmol mg-1 protein). Neither adenylate cyclase activation nor binding site characteristics were affected by capsaicin-induced denervation. In addition, hypotensive responses to intravenous boluses of rCGRP were examined in anaesthetized rats. Neither the basal blood pressure nor the blood pressure fall in response to rCGRP were altered by neonatal denervation by capsaicin. In conclusion, there is no evidence of denervation hypersensitivity of receptor mediated responses to CGRP in vivo or in vitro, following capsaicin-induced denervation in the rat. This suggests that CGRP is unlikely to exert a sustained tonic influence on cardiovascular regulation in the rat.

Nitric oxide and sensory nerves are involved in the vasodilator response to acetylcholine but not calcitonin gene-related peptide in rat skin microvasculature

1. The contributions of sensory nerves and nitric oxide (NO) to vasodilator responses to acetylcholine (ACh) and calcitonin gene-related peptide (CGRP) were examined in rat skin microvasculature with a laser Doppler flowmeter to monitor relative blood flow. 2. Perfusion of ACh (100 microM; for 30 min) over a blister base on the rat hind footpad elicited microvascular vasodilatation and this response was not sustained. CGRP (1 microM; 10 min perfusion) also elicited vasodilatation and this response was maintained even when CGRP was no longer in contact with the blister base. 3. The vasodilator response to ACh was significantly smaller in rats pretreated as neonates with capsaicin to destroy primary sensory afferents than it was in age-matched controls. The vasodilator response to CGRP was unaffected by capsaicin pretreatment. 4. Selective inhibitors of NO synthase, NG-nitro-L-arginine (L-NOARG) and NG-monomethyl-L-arginine (L-NMMA) (both at 100 microM) attenuated the vasodilator response to ACh in control rats, but had no effect on the vasodilator response to CGRP. There was a significant L-NOARG-resistant component in control rats while in capsaicin-treated rats the vasodilator response to ACh was virtually abolished by L-NOARG. The inactive stereoisomer NG-monomethyl-D-arginine (100 microM) did not affect the vasodilator response to ACh. 5. The efficacy of L-NOARG and L-NMMA as inhibitors of endothelium-dependent responses was confirmed by use of an endothelium-dependent vasodilator, the calcium ionophore A23187 (100 microM; 10 min perfusion). Vasodilatation to A23187 was strongly attenuated by both L-NOARG and L-NMMA.6. These results suggest that sensory nerves and NO are both involved in the dilatation produced by ACh in rat skin microvasculature. A component of the vasodilator response elicited by ACh involves a direct action on the microvascular endothelium with subsequent generation of NO, while an additional component is elicited via activation of sensory nerves. The vasodilator mediator(s) released by ACh from sensory nerves acts largely independently of NO.7. The vasodilator response to CGRP is independent of a prejunctional action on sensory nerves and of NO.

Effects of vasoactive neuropeptides on human saphenous vein

OBJECTIVE

To assess the role of neuropeptides in the control of vascular tone in the human saphenous vein the actions of substance P, vasoactive intestinal peptide, calcitonin gene related peptide, neuropeptide Y, and somatostatin on this blood vessel were examined.

METHODS

In vitro organ bath techniques were used with preparations of saphenous veins obtained from 29 patients (aged 41-66) who were undergoing coronary bypass surgery.

RESULTS

Substance P, vasoactive intestinal peptide, and calcitonin gene related peptide relaxed pre-constricted vessels in a dose dependent manner with a rapid onset of action, taking one to two minutes to reach a plateau at each dose. Substance P (10(-9) to 10(-6) mol/l) induced relaxation with a maximum response (mean (SEM)) 23.0 (6.6)% of the total relaxation induced by glyceryl trinitrate 1 microgram/ml and a 50% maximal effective concentration of 6.8 x 10(-9) mol/l. Vasoactive intestinal peptide (10(-10) to 10(-7) mol/l) produced a relaxation of 27.0 (5.1)% at 10(-7) mol/l. The maximum responses induced by substance P and vasoactive intestinal peptide were significantly reduced, to 3.7 (2.8)% and 4.7 (2.0)% respectively, after removal of the endothelium. Calcitonin gene related peptide (10(-10) to 10(-7) mol/l) elicited only 14.3 (2.6)% relaxation at 10(-7) mol/l, and this was not affected by removal of the endothelium. By contrast, neuropeptide Y and somatostatin exerted concentration dependent constriction on resting vessels. Neuropeptide Y (10(-10) to 10(-7) mol/l) caused prolonged contraction (roughly 20 minutes to reach a maximum plateau at each dose). At 10(-7) mol/l, the constriction amounted to 28.0 (12.0)% of the response to 90 mM KCl, in ring segments with or without endothelium. Somatostatin (10(-10) to 10(-6) mol/l) quickly caused contraction with a maximum response of 42.7 (15.0)% and a maximum response of 42.7 (15.0)% and a 50% maximal effective concentration of 6.7 x 10(-6) mol/l. The constriction was greatly increased when endothelium was removed, with a maximum response of 78.2 (16.8)% and a 50% maximal effective concentration of 4.3 x 10(-7) mol/l.

CONCLUSIONS

Vasoactive peptides have diverse effects on the vascular tone these effects are endothelium dependent. The exact physiological role and implication for performance of bypass grafts require further investigation.

Calcitonin gene-related peptide: multiple actions, multiple receptors

Calcitonin gene-related peptide (CGRP) shows diversity both in its effects and its receptors. It is likely to have roles as a neurotransmitter, neuromodulator, local hormone and trophic factor. Its effects include rapid changes in neuronal activity, relaxation of many types of smooth muscle, actions on metabolism and changes in gene expression. Receptor heterogeneity has been revealed from experiments comparing agonist potency ratios and antagonist affinities. The evidence from these approaches is reviewed in this article and a speculative receptor classification scheme is proposed. Some of the likely future directions for CGRP research are discussed.

Effects of calcitonin gene-related peptide on normal and atheromatous vessels and on resistance vessels in the coronary circulation in humans

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a potent dilator of normal epicardial coronary vessels in humans, but its effects on myocardial blood flow and atheromatous coronary vessel diameter are unknown.

METHODS AND RESULTS

Seven patients were entered for study of the effects of CGRP on coronary blood flow and 13 for the comparison of its effects on normal and atheromatous coronary arteries. In the first seven patients, left anterior descending artery (LAD) diameter at an angiographically normal site, coronary sinus oxygen saturation (CSO2S), systemic blood pressure, and heart rate were measured during intracoronary infusion of increasing concentrations of CGRP (up to 200 ng/ml at 2 ml/min) followed by intracoronary adenosine (0.267 micrograms/ml at 2 ml/min) and finally intracoronary glyceryl trinitrate (GTN) (5 micrograms/ml at 2 ml/min). CGRP dilated the normal segment of the LAD by 22.6 +/- 8% (mean +/- 95% confidence interval), p less than 0.001, with only a small increase in CSO2S from 40.1 +/- 2.7% to 47.3 +/- 2.7%, p less than 0.001. Adenosine, a potent dilator of myocardial resistance vessels, caused no further increase in LAD diameter but caused a rise in CSO2S from 47.3 +/- 2.7% to 76.0 +/- 2.7%, p less than 0.001. GTN caused no further increase in LAD diameter. As heart rate-blood pressure product remained unchanged throughout the study, the increase of CSO2S indicated only a small increase in myocardial blood flow after CGRP infusion. In 13 patients with atheromatous coronary artery disease, the effects of intracoronary CGRP at angiographically normal sites, stenoses, angiographically normal sites immediately adjacent to stenoses, and sites of coronary artery wall irregularity were compared after intracoronary infusion of a single dose of CGRP (200 ng/ml at 2 ml/min) followed by intracoronary GTN (5 micrograms/ml at 2 ml/min). At these four sites, CGRP resulted in dilatation by 17.0 +/- 5.6%, 15.3 +/- 12.1% (NS), 7.6 +/- 5.4% (NS), and 15.9 +/- 7.8%, respectively. There was no significant further dilatation after GTN at any of the four sites.

CONCLUSIONS

These data indicate that CGRP has little effect in humans at rest on coronary resistance vessels in nonischemic myocardium but causes marked dilatation of normal arteries and variable dilatation of atheromatous epicardial arteries.

Calcitonin gene-related peptide (CGRP) causes endothelium-dependent cyclic AMP, cyclic GMP and vasorelaxant responses in rat abdominal aorta

Calcitonin gene-related peptide (CGRP), a neuropeptide found in nerves surrounding most blood vessels, is a potent hypotensive agent in both humans and rats. In isolated strips of rat thoracic aorta, CGRP has been reported to cause endothelium-dependent relaxation. To study the cellular and molecular mechanisms involved in CGRP-induced vasodilation, we investigated the roles of two second messengers, cyclic AMP and cyclic GMP, as potential mediators of the signal transduction mechanism leading to vasodilation in response to CGRP in rat aorta. In the present study, the abdominal aorta, rather than thoracic aorta, was used because of its higher content of endogenous CGRP and, therefore, the greater likelihood of regulation by CGRP in vivo. Each abdominal aortic ring was precontracted with norepinephrine (NE) at its EC50 concentration (10-20 nM). CGRP (3-300 nM) caused concentration-dependent relaxations (reducing the NE-induced contractions by 34%) that were completely dependent on endothelium. The relaxations in response to CGRP were correlated in a time- and concentration-dependent manner with increases in aortic levels of both cyclic AMP and cyclic GMP. CGRP (100 nM) caused significant elevations of cyclic AMP levels (1.4 to 3.2 pmol/mg protein, at 1 min) and cyclic GMP levels (1.6 to 3.6 pmol/mg protein, at 30 s). Like the vasorelaxant responses, both cyclic AMP and cyclic GMP responses to CGRP were totally dependent on the endothelium. Pre-incubation with indomethacin (3 microM, 15 min) did not alter cyclic AMP responses to CGRP (100 nM), suggesting that prostaglandins are not involved. Therefore, CGRP-induced vasodilations of abdominal aorta involve an endothelium-dependent mechanism associated with cyclic GMP elevations, similar to the mechanisms of vasodilation in response to acetylcholine and other endothelium-dependent vasodilators. However, CGRP-induced relaxations of aorta involve an additional mechanism (i.e., endothelium-dependent cyclic AMP elevations), which may also contribute to the intracellular mechanism of aortic vasodilation in response to CGRP.

Calcitonin gene-related peptide (CGRP)-induced cyclic AMP, cyclic GMP and vasorelaxant responses in rat thoracic aorta are antagonized by blockers of endothelium-derived relaxant factor (EDRF)

The mechanism of CGRP-induced vasodilation in rat thoracic aorta was investigated using antagonists of the classical endothelium-derived vasorelaxant factor (EDRF) and comparisons with acetylcholine-induced vasodilations. The CGRP-induced relaxations of isolated rings of rat thoracic aorta were completely dependent on the presence of endothelium and were associated with increases in the levels of both cyclic AMP and cyclic GMP, the same as in our previous study using rat abdominal aorta. Maximum relaxations to CGRP, which represented 40-50% reversal of the norepinephrine-induced contractions, occurred with 100 nM CGRP. Addition of acetylcholine (ACh, 1 microM) to aortic rings, which were already maximally relaxed to CGRP, caused further relaxation to 100%, suggesting that CGRP may use a mechanism (or pool of EDRF) different from that of ACh. Both CGRP- and ACh-induced relaxations of aorta were significantly inhibited by the EDRF blocking agents, hemoglobin (10 microM), methylene blue (10 microM), and nordihydroguaiaretic acid (NDGA, 10 microM). In fact, hemoglobin and NDGA were more effective as inhibitors of CGRP-induced relaxations than ACh-induced relaxations. Hemoglobin, methylene blue and NDGA also inhibited the CGRP-induced increases in both cyclic AMP and cyclic GMP levels. On the other hand, indomethacin, a cyclo-oxygenase inhibitor, did not alter CGRP-induced vasorelaxations or increases in either cyclic AMP or cyclic GMP levels, suggesting that prostaglandins are not involved. Therefore, CGRP-induced vasodilations in rat thoracic aorta appear to involve EDRF, leading to cyclic GMP elevations in smooth muscle and ultimately vasorelaxations. However, another previously undescribed mechanism, which involves EDRF-dependent and indomethacin-resistant elevations of cyclic AMP levels, is triggered by CGRP in thoracic aorta. This novel EDRF-dependent cyclic AMP response may contribute to the CGRP-induced vasodilation in rat thoracic aorta.

Differential vasodilator profile of calcitonin gene-related peptide in porcine large and small diameter coronary artery rings

The vasodilator profile of calcitonin gene-related peptide (CGRP) was compared in large diameter (3-4 mm outer diameter) and small diameter (less than 1 mm outer diameter) rings from porcine left anterior descending coronary arteries (LAD). CGRP relaxed both sized rings in an endothelium-independent manner but was 10 X more potent in small compared to large diameter rings. Repeated administration of CGRP to small diameter rings did not cause the development of tolerance to its effects, whereas in the large diameter rings marked tolerance developed. Pretreatment with the CGRP peptide fragment, CGRP-(8-37) antagonised the vasodilator effects of CGRP in a concentration-dependent manner, but in large diameter rings, the antagonistic potency of CGRP-(8-37) was 10 X less than that seen in the small diameter rings. This differing vasodilator profile of CGRP in small and large diameter rings of pig LADs may be related to a differential CGRP receptor distribution along their length.

Heterogeneous involvement of endothelium in calcitonin gene-related peptide-induced relaxation in coronary arteries from rat

1. The effects of rat- and human-CGRP and capsaicin were studied in isolated rings of rat proximal epicardial (PC) and distal intramyocardial (DC) coronary arteries. 2. The relaxing effect of rat-CGRP was dependent on the level of vessel tone induced by prostaglandin F2 alpha (PGF2 alpha) in PC but not in DC arteries. Submaximally contracted DC and PC arteries were more sensitive to rat- than human-CGRP. There was no difference in sensitivity to rat- and human-CGRP between PC and DC arteries. 3. Substance P elicited a small relaxation only in 4 of the 6 PC arteries tested. PC and DC arteries were concentration-dependently relaxed by capsaicin. The relaxation was partly inhibited by ruthenium red, thus suggesting that capsaicin causes specific release of CGRP from sensory nerve endings in rat coronary arteries. 4. The relaxant effect of rat-CGRP was antagonized by endothelium removal and indomethacin but not methylene blue in endothelium-intact PC arteries. The relaxation in DC arteries was not affected by any of these treatments, indicating a heterogeneous involvement of the endothelium in CGRP-mediated coronary vasodilatation and the release of a cyclo-oxygenase product in PC arteries in rats. 5. Glibenclamide had no inhibitory effect on the CGRP-induced relaxation of PC and DC arteries, thus excluding the involvement of glibenclamide-sensitive K(+)-channels in the mechanism of action of CGRP in rat coronary arteries.

The effects of calcitonin gene-related peptide (CGRP) on cochlear and mucosal blood flow in the albino rabbit

The effects of intravenously infused calcitonin gene-related peptide (CGRP) on the regional blood flow of the cochlea, the middle ear and the upper respiratory tract were studied. Two series of experiments were performed without pretreatment on either conscious or pentobarbital anaesthetized animals; in one series the cervical sympathetic chain was severed on one side; in another series anaesthetized animals were subjected to ganglionic blockade with hexamethonium bromide in order to abolish reflexes involving the autonomic nervous system. In still another series conscious animals were pretreated with indomethacin in order to reduce the formation of prostaglandins. In all groups of animals where sympathetic influence was diminished cochlear blood flow increased during the infusion of CGRP. In the mucosa of middle ear and the upper airways, the blood flow increased in all groups. The results indicate that CGRP at these doses causes vasorelaxation in the mucosa of the middle ear and upper airways and does so also in the cochlea if the sympathetic influence is abolished.

The role of neuropeptides in cardiovascular regulation

During the past few years more than 30 novel, biologically active peptides have been discovered. Some are produced in endocrine glands and circulate as hormones in the blood; others are contained in the enterochromaffin cells of the gut and may be involved in the regulation of intestinal functions. The vast majority of new peptides, however, have been detected in the central and peripheral nervous systems, where they are synthesized in distinct neurons and stored in neurovesicles. Many of these neuropeptides may be involved in circulatory regulation. There is evidence supporting such a role, especially for centrally located angiotensin, opioid peptides, substance P, neuropeptide Y (NPY), vasopressin, atrial natriuretic peptide (ANP), kinins, corticotropin releasing factor, bombesin, and somatostatin. In this review we discuss the cardiovascular actions of angiotensin, neuropeptide Y, and calcitonin gene related peptide.

Cutaneous blood flow responses in the forearms of Raynaud's patients induced by local cooling and intradermal injections of CGRP and histamine

1. The cutaneous responses of the forearm to local cold exposure and intradermal injection of CGRP and other vasoactive mediators were compared in primary Raynaud's sufferers and normal volunteers. 2. Skin responses in the forearm were measured in terms of erythema reddening and skin blood flow. Visual responses were recorded by tracing and then area calculated by computerised planimetry. Skin blood flow was measured using a laser Doppler blood flow meter. 3. Cooling (5-6 degrees C for 2 min) of a 1 cm2 area of the forearm caused a localised reactive hyperaemia response in normal volunteers, measured using the last Doppler blood flow meter. The peak response in Raynaud's patients was significantly smaller than that of normal volunteers. 4. The cutaneous responses of Raynaud's patients and normal volunteers to intradermal injections of CGRP, histamine and PGE2 were not significantly different. 5. The results suggest that Raynaud's sufferers do not exhibit a diminished response to CGRP in the cutaneous microvasculature and can respond normally to histamine with an axon reflex mediated flare.

Mediation of prolonged increases in nasal mucosal blood flow by calcitonin gene-related peptide (CGRP)

Calcitonin gene-related peptide (CGRP) is a vasoactive and smooth muscle contractile neuropeptide, which is released during human nasal allergic reactions. Mean values for nasal blood flow (NBF), quantified in each nostril by a laser Doppler technique, varied no more than +/- 25% of a mean initial reading in normal human subjects over 4 hr in a controlled environment. Intranasal administration of multiple doses of CGRP to 17 normal subjects stimulated significant mean increases in NBF at 30-1000 ng of CGRP, with maximal mean rises of 86-130% after 100 and 300 ng of CGRP. Delivery of incremental doses of CGRP every 30 min for 2 hr evoked repetitive responses without tachyphylaxis. A single vasoactive dose of CGRP, which achieved nasal fluid concentrations similar to those elicited by antigen challenge, elicited the sensation of nasal obstruction in most subjects at 1 hr and for up to 4 hr after CGRP, without elevating nasal fluid concentrations of histamine. CGRP thus is a potent histamine-independent mediator of allergic reactions.

Sensory nerves, vascular endothelium and neurogenic relaxation of the guinea-pig isolated pulmonary artery

1. In the presence of atropine and guanethidine (3 mumol/l each), electrical field stimulation (1-20 Hz) produced frequency-dependent relaxations of the histamine- (3 mumol/l) induced vascular tone in isolated rings from the guinea-pig pulmonary artery. The electrically-evoked relaxations were abolished by tetrodotoxin (1 mumol/l). The amplitude of these nerve-mediated, non-adrenergic non-cholinergic (NANC) relaxations was unaffected by removal of the vascular endothelium produced through rubbing of the internal surface. 2. Capsaicin (1 mumol/l) produced a prompt and sustained relaxation of the histamine-induced tone which was unaffected by removal of the endothelium. A second application of capsaicin 60-120 min later had no further relaxant effect, indicating desensitization. After in vitro capsaicin desensitization, the electrically-evoked NANC relaxations were abolished, both in the presence or absence of the vascular endothelium. 3. Substance P evoked a prompt and transient relaxation in precontracted arterial rings with intact endothelium and a transient small contraction in rings in which the endothelium had been mechanically removed. The selective NK-1 receptor agonist, [Pro9]-substance P sulfone closely mimicked the relaxation produced by substance P while the selective NK-2 or NK-3 receptor agonists had no relaxant effect. Tachyphylaxis to substance P did not modify the amplitude of the capsaicin-induced relaxation. 4. Human alpha calcitonin gene-related peptide (CGRP) produced a prompt and sustained relaxation both in the presence and absence of the vascular endothelium. 5. Ruthenium red (10 mumol/l) blocked the relaxation to capsaicin while leaving unaffected the relaxation to electrical field stimulation or CGRP (0.1 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular relaxation properties of calcitonin gene-related peptide and vasoactive intestinal polypeptide in subarachnoid hemorrhage

The vascular relaxation effects of calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) on the dog basilar artery after experimentally produced subarachnoid hemorrhage (SAH) were examined in vitro by an isometric tension recording method. Both CGRP and VIP induced dose-dependent relaxations in ring segments of the intact basilar artery of control dogs. The vasorelaxant action of CGRP was more potent than that of VIP. The single-injection model of SAH was produced by injection of fresh autologous arterial blood (1 ml/kg body weight) into the cisterna magna on Day 0 of the post-SAH period, and the double-injection model was produced by two injections of blood (0.5 ml/kg each) on Days 0 and 2. Narrowing of the basilar arteries on vertebral angiograms was most prominent on Day 3 or 7 in the single- or double-injection model, respectively. Relaxation of the basilar artery induced by CGRP and VIP was to some extent decreased on Days 3 and 7 of the post-SAH period in the single-injection model, and on Days 7 and 14 in the double-injection model. However, the vasorelaxant effects of CGRP and VIP were significantly enhanced on Day 14 of the post-SAH period in the single-injection model, and on Days 28 and 42 in the double-injection model. Subsequently, these effects returned to control levels by Days 28 or 63 in the single- or double-injection model, respectively.