Calcitonin gene-related peptide stimulates cyclic AMP formation in rat aortic smooth muscle cells

Targeting temperature-sensitive transient receptor potential channels in hypertension: far beyond the perception of hot and cold

Transient receptor potential (TRP) channels are nonselective cation channels and participate in various physiological roles. Thus, changes in TRP channel function or expression have been linked to several disorders. Among the many TRP channel subtypes, the TRP ankyrin type 1 (TRPA1), TRP melastatin type 8 (TRPM8), and TRP vanilloid type 1 (TRPV1) channels are temperature-sensitive and recognized as thermo-TRPs, which are expressed in the primary afferent nerve. Thermal stimuli are converted into neuronal activity. Several studies have described the expression of TRPA1, TRPM8, and TRPV1 in the cardiovascular system, where these channels can modulate physiological and pathological conditions, including hypertension. This review provides a complete understanding of the functional role of the opposing thermo-receptors TRPA1/TRPM8/TRPV1 in hypertension and a more comprehensive appreciation of TRPA1/TRPM8/TRPV1-dependent mechanisms involved in hypertension. These channels varied activation and inactivation have revealed a signaling pathway that may lead to innovative future treatment options for hypertension and correlated vascular diseases.

Pharmacological Profile of the Purinergic P2Y Receptors That Modulate, in Response to ADPβS, the Vasodepressor Sensory CGRPergic Outflow in Pithed Rats

Calcitonin gene-related peptide (CGRP), an endogenous neuropeptide released from perivascular sensory nerves, exerts a powerful vasodilatation. Interestingly, adenosine triphosphate (ATP) stimulates the release of CGRP by activation of prejunctional P2X_2/3 receptors, and adenosine 5'-O-2-thiodiphosphate (ADPβS), a stable adenosine diphosphate (ADP) analogue, produces vasodilator/vasodepressor responses by endothelial P2Y₁ receptors. Since the role of ADP in the prejunctional modulation of the vasodepressor sensory CGRPergic drive and the receptors involved remain unknown, this study investigated whether ADPβS inhibits this CGRPergic drive. Accordingly, 132 male Wistar rats were pithed and subsequently divided into two sets. In set 1, ADPβS (5.6 and 10 µg/kg·min) inhibited the vasodepressor CGRPergic responses by electrical stimulation of the spinal T₉-T₁₂ segment. This inhibition by ADPβS (5.6 µg/kg·min) was reverted after i.v. administration of the purinergic antagonists MRS2500 (300 µg/kg; P2Y₁) or MRS2211 (3000 µg/kg; P2Y₁₃), but not by PSB0739 (300 µg/kg; P2Y₁₂), MRS2211 (1000 µg/kg; P2Y₁₃) or the K_ATP blocker glibenclamide (20 mg/kg). In set 2, ADPβS (5.6 µg/kg·min) failed to modify the vasodepressor responses to exogenous α-CGRP. These results suggest that ADPβS inhibits CGRP release in perivascular sensory nerves. This inhibition, apparently unrelated to activation of ATP-sensitive K⁺ channels, involves P2Y₁ and probably P2Y₁₃, but not P2Y₁₂ receptors.

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

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.

Calcitonin gene-related peptide inhibits angiotensin II-induced NADPH oxidase-dependent ROS via the Src/STAT3 signalling pathway

We had previously demonstrated that the calcitonin gene‐related peptide (CGRP) suppresses the oxidative stress and vascular smooth muscle cell (VSMC) proliferation induced by vascular injury. A recent study also indicated that CGRP protects against the onset and development of angiotensin II (Ang II)‐induced hypertension, vascular hypertrophy and oxidative stress. However, the mechanism behind the effects of CGRP on Ang II‐induced oxidative stress is unclear. CGRP significantly suppressed the level of reactive oxygen species (ROS) generated by NADPH oxidase in Ang II‐induced VSMCs. The Ang II‐stimulated activation of both Src and the downstream transcription factor, STAT3, was abrogated by CGRP. However, the antioxidative effect of CGRP was lost following the expression of constitutively activated Src or STAT3. Pre‐treatment with H‐89 or CGRP_8–37 also blocked the CGRP inhibitory effects against Ang II‐induced oxidative stress. Additionally, both in vitro and in vivo analyses show that CGRP treatment inhibited Ang II‐induced VSMC proliferation and hypertrophy, accompanied by a reduction in ROS generation. Collectively, these results demonstrate that CGRP exhibits its antioxidative effect by blocking the Src/STAT3 signalling pathway that is associated with Ang II‐induced VSMC hypertrophy and hyperplasia.

The Regulation of Pulmonary Vascular Tone by Neuropeptides and the Implications for Pulmonary Hypertension

Pulmonary hypertension (PH) is an incurable, chronic disease of small pulmonary vessels. Progressive remodeling of the pulmonary vasculature results in increased pulmonary vascular resistance (PVR). This causes secondary right heart failure. PVR is tightly regulated by a range of pulmonary vasodilators and constrictors. Endothelium-derived substances form the basis of most current PH treatments. This is particularly the case for pulmonary arterial hypertension. The major limitation of current treatments is their inability to reverse morphological changes. Thus, there is an unmet need for novel therapies to reduce the morbidity and mortality in PH. Microvessels in the lungs are highly innervated by sensory C fibers. Substance P and calcitonin gene-related peptide (CGRP) are released from C-fiber nerve endings. These neuropeptides can directly regulate vascular tone. Substance P tends to act as a vasoconstrictor in the pulmonary circulation and it increases in the lungs during experimental PH. The receptor for substance P, neurokinin 1 (NK1R), mediates increased pulmonary pressure. Deactivation of NK1R with antagonists, or depletion of substance P prevents PH development. CGRP is a potent pulmonary vasodilator. CGRP receptor antagonists cause elevated pulmonary pressure. Thus, the balance of these peptides is crucial within the pulmonary circulation (Graphical Abstract). Limited progress has been made in understanding their impact on pulmonary pathophysiology. This is an intriguing area of investigation to pursue. It may lead to promising new candidate therapies to combat this fatal disease. This review provides a summary of the current knowledge in this area. It also explores possible future directions for neuropeptides in PH.

Calcitonin gene-related peptide: neuroendocrine communication between the pancreas, gut, and brain in regulation of blood glucose

Background

Calcitonin gene-related peptide (CGRP), a ubiquitous neuropeptide, plays a diverse and intricate role in chronic low-grade inflammation, including conditions such as obesity, type 2 diabetes, and diabetes of the exocrine pancreas. Diabetes of exocrine pancreas is characterised by chronic hyperglycemia and is associated with persistent low-grade inflammation and altered secretion of certain pancreatic and gut hormones. While CGRP may regulate glucose homeostasis and the secretion of pancreatic and gut hormones, its role in chronic hyperglycemia after acute pancreatitis (CHAP) is not known. The aim of this study was to investigate the association between CGRP and CHAP.

Methods

Fasting blood samples were collected to measure insulin, HbA1c, CGRP, amylin, C-peptide, glucagon, pancreatic polypeptide (PP), somatostatin, gastric inhibitory peptide, glicentin, glucagon-like peptide-1 and 2, and oxyntomodulin. Modified Poisson regression analysis and linear regression analyses were conducted. Five statistical models were used to adjust for demographic, metabolic, and pancreatitis-related risk factors.

Results

A total of 83 patients were recruited. CGRP was significantly associated with CHAP in all five models (P-trend <0.005). Further, it was significantly associated with oxyntomodulin (P<0.005) and glucagon (P<0.030). Oxyntomodulin and glucagon independently contributed 9.7% and 7%, respectively, to circulating CGRP variance. Other pancreatic and gut hormones were not significantly associated with CGRP.

Conclusions

CGRP is involved in regulation of blood glucose in individuals after acute pancreatitis. This may have translational implications in prevention and treatment of diabetes of the exocrine pancreas.

Calcitonin gene-related peptide: physiology and pathophysiology

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide. Discovered 30 years ago, it is produced as a consequence of alternative RNA processing of the calcitonin gene. CGRP has two major forms (α and β). It belongs to a group of peptides that all act on an unusual receptor family. These receptors consist of calcitonin receptor-like receptor (CLR) linked to an essential receptor activity modifying protein (RAMP) that is necessary for full functionality. CGRP is a highly potent vasodilator and, partly as a consequence, possesses protective mechanisms that are important for physiological and pathological conditions involving the cardiovascular system and wound healing. CGRP is primarily released from sensory nerves and thus is implicated in pain pathways. The proven ability of CGRP antagonists to alleviate migraine has been of most interest in terms of drug development, and knowledge to date concerning this potential therapeutic area is discussed. Other areas covered, where there is less information known on CGRP, include arthritis, skin conditions, diabetes, and obesity. It is concluded that CGRP is an important peptide in mammalian biology, but it is too early at present to know if new medicines for disease treatment will emerge from our knowledge concerning this molecule.

CGRP in the trigeminovascular system: a role for CGRP, adrenomedullin and amylin receptors?

The neuropeptide calcitonin gene-related peptide (CGRP) is reported to play an important role in migraine. It is expressed throughout the trigeminovascular system. Antagonists targeting the CGRP receptor have been developed and have shown efficacy in clinical trials for migraine. However, no CGRP antagonist is yet approved for treating this condition. The molecular composition of the CGRP receptor is unusual because it comprises two subunits; one is a GPCR, the calcitonin receptor-like receptor (CLR). This associates with receptor activity-modifying protein (RAMP) 1 to yield a functional receptor for CGRP. However, RAMP1 also associates with the calcitonin receptor, creating a receptor for the related peptide amylin but this also has high affinity for CGRP. Other combinations of CLR or the calcitonin receptor with RAMPs can also generate receptors that are responsive to CGRP. CGRP potentially modulates an array of signal transduction pathways downstream of activation of these receptors, in a cell type-dependent manner. The physiological significance of these signalling processes remains unclear but may be a potential avenue for refining drug design. This complexity has prompted us to review the signalling and expression of CGRP and related receptors in the trigeminovascular system. This reveals that more than one CGRP responsive receptor may be expressed in key parts of this system and that further work is required to determine their contribution to CGRP physiology and pathophysiology.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

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.

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.

Role of calcitonin gene-related peptide in bone repair after cyclic fatigue loading

Background

Calcitonin gene related peptide (CGRP) is a neuropeptide that is abundant in the sensory neurons which innervate bone. The effects of CGRP on isolated bone cells have been widely studied, and CGRP is currently considered to be an osteoanabolic peptide that has effects on both osteoclasts and osteoblasts. However, relatively little is known about the physiological role of CGRP in-vivo in the skeletal responses to bone loading, particularly fatigue loading.

Methodology/Principal Findings

We used the rat ulna end-loading model to induce fatigue damage in the ulna unilaterally during cyclic loading. We postulated that CGRP would influence skeletal responses to cyclic fatigue loading. Rats were fatigue loaded and groups of rats were infused systemically with 0.9% saline, CGRP, or the receptor antagonist, CGRP_8–37, for a 10 day study period. Ten days after fatigue loading, bone and serum CGRP concentrations, serum tartrate-resistant acid phosphatase 5b (TRAP5b) concentrations, and fatigue-induced skeletal responses were quantified. We found that cyclic fatigue loading led to increased CGRP concentrations in both loaded and contralateral ulnae. Administration of CGRP_8–37 was associated with increased targeted remodeling in the fatigue-loaded ulna. Administration of CGRP or CGRP_8–37 both increased reparative bone formation over the study period. Plasma concentration of TRAP5b was not significantly influenced by either CGRP or CGRP_8–37 administration.

Conclusions

CGRP signaling modulates targeted remodeling of microdamage and reparative new bone formation after bone fatigue, and may be part of a neuronal signaling pathway which has regulatory effects on load-induced repair responses within the skeleton.

Endothelium removal augments endothelium-independent vasodilatation in rat mesenteric vascular bed

BACKGROUND AND PURPOSE

The vascular endothelium regulates vascular tone by releasing various endothelium-derived vasoactive substances to counteract excess vascular response. We investigated whether the vascular endothelium regulates vasodilatation via released endothelium-derived contracting factors (EDCFs), by examining the effect of endothelium removal on responses to periarterial nerve stimulation (PNS) and various vasodilator agents.

EXPERIMENTAL APPROACH

The rat mesenteric vascular bed was perfused with Krebs solution. Vasodilator responses to PNS and 5 min perfusion of vasodilator agents in preparations with endothelium were compared with those in the same preparations without endothelium. The endothelium was removed by 30 s perfusion with sodium deoxycholate.

KEY RESULTS

Endothelium removal significantly augmented vasodilator responses to PNS and calcitonin gene-related peptide (CGRP), isoprenaline (beta-adrenoceptor agonist), SNP and 8-bromo-cGMP (8-Br-cGMP; cGMP analogue) but not BAY41-2272 (soluble guanylate cyclase activator). The augmentation of SNP-induced vasodilatation after denudation was much greater than that of CGRP- or isoprenaline-induced vasodilatation. In the preparations with an intact endothelium, L-NAME (nitric oxide synthase inhibitor) significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and 8-Br-cGMP, but not BAY41-2272. Indomethacin (cyclooxygenase inhibitor) and seratrodast (thromboxane A(2) receptor antagonist), but not phosphoramidon (endothelin-1-converting enzyme inhibitor) or BQ-123 (selective endothelin type A receptor antagonists), significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and BAY41-2272.

CONCLUSION AND IMPLICATION

These results suggest that the endothelium in rat mesenteric arteries regulates and maintains vascular tone via counteracting not only vasoconstriction through releasing endothelium-derived relaxing factors, but also vasodilatation, in part by releasing an EDCF, thromboxane A(2).

Calcitonin gene-related peptide affects synaptic and membrane properties of bronchial parasympathetic neurons

Calcitonin gene-related peptide (CGRP) is located with substance P in nerve varicosities in close apposition to principal neurons in airway parasympathetic ganglia. Substance P has multiple effects on airway parasympathetic neurons but the role of CGRP is unknown. Using intracellular current clamp recording of ganglionic neurons, stimulation of vagal afferent nerves in the presence of neurokinin receptor antagonists evoked hyperpolarization of the membrane potential which was blocked by the CGRP-1 receptor antagonist, CGRP(8-37). Exogenous application of alpha-CGRP (0.001-0.1 microM) hyperpolarized the membrane potential, which was either blocked or reversed to depolarization in the presence of CGRP(8-37), whereas higher concentrations of alpha-CGRP (1.0-10.0 microM) caused depolarization. Action potential accommodation in phasic-type neurons decreased in the presence of alpha-CGRP (0.1-10 microM). The co-localization of substance P- and CGRP-immunoreactivity was observed in nerve varicosities within ganglia; prolonged exposure to capsaicin in vitro depleted substance P and CGRP immunostaining in nerve varicosities. These results demonstrate that CGRP has multiple effects on the excitability of airway parasympathetic neurons and may alter their activity, ultimately affecting parasympathetic tone in the lower airways.

The early effects of chronic hypoxia on the cardiovascular system in the rat: role of nitric oxide

Experiments were performed under Saffan anaesthesia on normoxic (N) rats and on chronically hypoxic rats exposed to 12% O2 for 1, 3 or 7 days (1, 3 or 7CH rats): N rats routinely breathed 21% O2 and CH rats 12% O2. The 1, 3 and 7CH rats showed resting hyperventilation relative to N rats, but baseline heart rate (HR) was unchanged and arterial blood pressure (ABP) was lowered. Femoral vascular conductance (FVC) was increased in 1 and 3CH rats, but not 7CH rats. When 1-7CH rats were acutely switched to breathing 21% O2 for 5 min, ABP increased and FVC decreased, consistent with removal of a hypoxic dilator stimulus that is waning in 7CH rats. We propose that this is because the increase in haematocrit and vascular remodelling in skeletal muscle help restore the O2 supply. The increases in FVC evoked by acute hypoxia (8% O2 for 5 min) and by infusion for 5 min of alpha-calcitonin gene-related peptide (alpha-CGRP), which are NO-dependent, were particularly accentuated in 1CH, relative to N rats. The NO synthesis inhibitor L-NAME increased ABP, decreased HR and greatly reduced FVC, and attenuated increases in FVC evoked by acute hypoxia and alpha-CGRP, such that baselines and responses were similar in N and 1-7CH rats. We propose that in the first few days of chronic hypoxia there is tonic NO-dependent vasodilatation in skeletal muscle that is associated with accentuated dilator responsiveness to acute hypoxia and dilator substances that are NO -dependent.

Calcitonin gene-related peptide receptor activation by receptor activity-modifying protein-1 gene transfer to vascular smooth muscle cells

The neuropeptide calcitonin gene-related peptide (CGRP) is a potent vasodilator that plays a protective role in the cardiovascular system. The receptor for CGRP is an unusual complex of the G protein-coupled calcitonin-like receptor and an obligate receptor activity modifying protein-1 (RAMP1). In this report we provide the first evidence that RAMP1 is rate limiting in vascular smooth muscle cells. Although cultured rat aorta smooth muscle cells express calcitonin like-receptor and RAMP1, we found that CGRP is not a potent activator of the receptor. After overexpression of RAMP1 by adenoviral gene transfer, there was a striking increase in CGRP-induced production of cAMP, with a 75-fold decrease in the EC(50) and a 1.5-fold increase in the maximal response. The biological consequence of this increased receptor activity was observed in three different paradigms. First, RAMP1 gene transfer caused a CGRP-dependent decrease in cell proliferation. Second, RAMP1 and CGRP treatment led to a 3-fold greater free radical-induced reduction in cell number. Finally, RAMP1 gene transfer resulted in a 5-fold CGRP-dependent increase in terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling-positive apoptotic cells upon serum withdrawal. The mechanisms underlying these effects involved cAMP-dependent pathways. We propose that RAMP1 gene transfer may be an effective strategy for increasing the effectiveness of CGRP-induced decrease in restenosis after aortic angioplasty.

Ca2+ signaling in human fetoplacental vasculature: effect of CGRP on umbilical vein smooth muscle cytosolic Ca2+ concentration

CGRP is a potent vasodilator with increased levels in fetoplacental circulation during late pregnancy. We have recently demonstrated that acute CGRP exposure to fetoplacental vessels in vitro induced vascular relaxation, but the signaling pathway of CGRP in fetoplacental vasculature remains unclear. We hypothesized that CGRP relaxes fetoplacental vasculature via regulating smooth muscle cytosolic Ca2+ concentrations. In the present study, by using human umbilical vein smooth muscle (HUVS) cells (HUVS-112D), we examined CGRP receptors, cAMP generation, and changes in cellular Ca2+ concentrations on CGRP treatment. These cells express mRNA for CGRP receptor components, calcitonin receptor-like receptor, and receptor activity-modifying protein-1. Direct saturation binding for 125I-labeled CGRP to HUVS cells and Scatchard analysis indicate specificity of the receptors for CGRP [dissociation constant (K(D)) = 67 nM, maximum binding capcity (Bmax) = 2.7 pmol/million cells]. Exposure of HUVS cells to CGRP leads to a dose-dependent increase in intracellular cAMP accumulation, and this increase is prevented by CGRP antagonist CGRP(8-37). Using fura-2-loaded HUVS cells, we monitored the effects of CGRP on intracellular Ca2+ concentration ([Ca2+]i). In the presence of extracellular Ca2+, bradykinin (10(-6) M), a fetoplacental vasoconstrictor, increases HUVS cells [Ca2+]i concentration. CGRP (10(-8) M) abolishes bradykinin-induced [Ca2+]i elevation. When the cells were pretreated with glibenclamide, an ATP-sensitive potassium channel blocker, the CGRP actions on bradykinin-induced Ca2+ influx were profoundly inhibited. In the absence of extracellular Ca2+, CGRP (10(-8) M) attenuated the increase of [Ca2+]i induced by a sarcoplasmic reticulum Ca2+ pump ATPase inhibitor thapsigargin (10(-5) M). Furthermore, Rp-cAMPS, a cAMP-dependent protein kinase A inhibitor, blocks CGRP actions on thapsigargin-induced Ca2+ release from sarcoplasmic reticulum. Our results suggested that CGRP relaxes human fetoplacental vessels by not only inhibiting the influx of extracellular Ca2+ but also attenuating the release of intracellular Ca2+ from the sarcoplasmic reticulum, and these actions might be attributed to CGRP-induced intracellular cAMP accumulation.

Calcitonin gene-related peptide regulates gene transcription in primary afferent neurons

Although primary afferent neurons express receptors for calcitonin gene-related peptide (CGRP), understanding of the cellular effects of these receptors is limited. We determined that CGRP receptors regulate gene transcription in primary afferent neurons through a cyclic AMP (cAMP)-dependent pathway. CGRP increased cAMP in neonatal dorsal root ganglion (DRG) neurons in a concentration-dependent manner that was blocked by the receptor antagonist CGRP(8-37). The response to CGRP also occurred in adult DRG cells. In contrast, CGRP did not alter the concentration of free intracellular calcium in neonatal or adult DRG neurons. Immunohistochemical data showed that one downstream effect of the cAMP signaling pathway was phosphorylation of cAMP response element binding (CREB) protein, suggesting that CGRP regulates gene expression. This interpretation was supported by evidence that CGRP increased CRE-dependent gene transcription in neurons transiently transfected with a CRE-luciferase DNA reporter construct. The effect of CGRP on gene transcription was inhibited by H89, myristoylated-protein kinase A inhibitor(14-22)-amide and U0126, indicating that protein kinase A and mitogen-activated protein kinase/extracellular receptor kinase kinase are enzymes that mediate effects of CGRP on gene transcription. Therefore, CGRP receptors may regulate expression of proteins by primary afferent neurons during development and in response to tissue-damaging stimuli.

Mechanisms involved in calcitonin gene-related Peptide-induced relaxation in pregnant rat uterine artery

Human and rodent studies have demonstrated that calcitonin gene-related peptide (CGRP), a potent vasodilator, relaxes uterine tissue during pregnancy but not during labor. The vascular sensitivity to CGRP is enhanced during pregnancy, compared to nonpregnant human uterine arteries. In the present study, we hypothesized that uterine artery relaxation effects of CGRP are enhanced in pregnant rats compared to nonpregnant diestrus rats (NP-DE) and that several secondary messenger systems are involved in this process. We also hypothesized that the expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP1), and CGRP-B receptors are greater in pregnant rats. For vascular relaxation studies, uterine arteries from either NP-DE or Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP-A and CGRP-B receptor expressions were assessed by RT-PCR and Western immunoblotting, respectively. CGRP (10(-10)--10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in both NP-DE and Day 18 pregnant rat uterine arteries. Pregnancy increased the vasodilator sensitivity to CGRP significantly (P < 0.05) compared to NP-DE rats. CGRP receptor antagonist, CGRP8-37, inhibited CGRP-induced relaxation of pregnant uterine arteries. The CGRP-induced relaxation was not affected by NG-nitro-l-arginine methyl ester (L-NAME) (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by inhibitors of guanylate cyclase (ODQ, 10(-5) M) and adenylate cyclase (SQ 22536, 10(-5) M). CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by potassium channel blockers KATP (glybenclamide, 10(-5) M) and K(CA) (tetraethylammonium, 10(-3) M). The expression of CRLR and RAMP1 was significantly (P < 0.05) elevated during pregnancy compared to nonpregnant diestrus state (NP-DE). However, CGRP-B receptor proteins in uterine arteries were not altered with pregnancy compared to those of NP-DE. These studies suggest that CGRP-induced increases in uterine artery relaxation may play a role in regulating blood flow to the uterus during pregnancy and, therefore, in fetal growth and survival.

Sex steroid hormones enhance hypotensive effects of calcitonin gene-related Peptide in aged female rats

The aim of the present study is to investigate whether vascular protective effects of steroid hormones in aged female rats are mediated through calcitonin gene-related peptide (CGRP), a known potent vasodilator. This rat model reflects the postmenopausal state in humans. We examined whether blood pressure lowering effects of CGRP are enhanced in aged female rats when steroid hormone treatments are administered. We observed that 1) continuous infusion of CGRP lowered blood pressures in rats treated with estradiol-17beta and progesterone (P < 0.05), 2) acute hypotensive effects of CGRP were significantly (P < 0.05) greater in the presence of steroid hormones than in vehicle-treated groups, 3) blood pressure decreases in response to CGRP are lower in aged female rats than they are in young adult ovariectomized rats, and 4) age-related differences in the hypotensive effects of CGRP were nullified when animals were treated with steroid hormones. These data suggest that female sex steroid hormones may modulate arterial blood pressure by regulating the CGRP effector system in female rats regardless of age.

Characterization of CGRP(1) receptors in the guinea pig basilar artery

The purpose of the present study was to characterise receptors mediating calcitonin gene-related peptide (CGRP)-induced relaxation of guinea pig basilar artery. This was done by investigating vasomotor responses in vitro and performing autoradiographic binding studies. We also intended to study the importance of an intact endothelium. Agonist studies showed that peptides of the CGRP family induced relaxation of the guinea pig basilar artery with the following order of potency: human beta-CGRP=human alpha-CGRP>>adrenomedullin=[acetamidomethyl-Cys(2,7)]alpha-human CGRP ([Cys(ACM)(2,7)]CGRP)=amylin. These data are in concord with those of the autoradiographic binding studies that showed displacement of [125I] human alpha-CGRP binding with the following order of potency: human alpha-CGRP=human beta-CGRP>>adrenomedullin=human alpha-CGRP-(8-37)>>Cys(ACM)(2,7)]CGRP. In blockade experiments, the relaxant responses to human alpha- and human beta-CGRP were competitively blocked by the CGRP(1) receptor antagonist human alpha-CGRP-(8-37), while those of adrenomedullin and amylin were blocked non-competitively. In order to examine whether amylin induced relaxation via amylin or CGRP receptors, we studied the antagonistic effect of amylin-(8-37) on the weak relaxant response to amylin and found that it was not blocked by amylin-(8-37). These findings, together with the finding that the CGRP(2) receptor agonist [Cys(ACM)(2,7)]CGRP only induced a weak relaxation in the highest concentrations examined, suggest that the CGRP family of peptides mediate relaxation by CGRP(1)-type receptors. Removal of the endothelium, the addition of N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue or indomethacin did not affect the concentration-response curves of the CGRP analogues, neither in the presence nor in the absence of human CGRP-(8-37). The study shows the presence of a relaxant CGRP(1) receptor on the smooth muscle cells of guinea pig basilar artery. Various endothelial factors did not influence relaxant responses.

Relaxation of myometrium by calcitonin gene-related peptide is independent of nitric oxide synthase activity in mouse uterus

Calcitonin gene-related peptide (CGRP) inhibits myometrial contractile activity. However, the responsiveness of the mouse myometrium to CGRP is dependent on the hormonal and gestational stage. The inhibitory effect of CGRP in the myometrium is prominent during gestation and declines at parturition. The present study was undertaken to examine if nitric oxide (NO) production by nitric oxide synthase (NOS) isoforms mediates the inhibitory action of CGRP on uterine contractions as has been suggested earlier. Transgenic mice deficient in either of the three major NOS isoforms: endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) were used. Isometric force measurements on myometrial strips obtained from NOS-deficient mice were carried out and the inhibitory capacity of CGRP was monitored. CGRP inhibited KCl-induced contractions of the myometrial strips obtained from eNOS(-/-), iNOS(-/-), and nNOS(-/-) mice with equal efficiency as in wild-type animals. Additionally, NOS protein expression in the mouse uterus during gestation and during the estrous cycle was examined by means of Western immunoblot analysis. No correlation between NOS expression and inhibitory activity of CGRP was evident. The results suggest that the inhibitory action of CGRP in the mouse uterus is independent of the activity of these NOS isoforms.

Mechanisms of calcitonin gene-related peptide-induced increases of pulmonary blood flow in fetal sheep

Fetal pulmonary blood flow is regulated by various vasoactive substances. One, calcitonin gene-related peptide (CGRP), increases pulmonary blood flow. We examined four key physiological mechanisms underlying this response using the blocker drugs CGRP receptor blocker (CGRP(8-37)), nitric oxide synthase inhibitor [N(omega)-nitro-L-arginine (L-NNA)], adenosine triphosphate-dependent potassium (K(ATP)) channel blocker (glibenclamide), and cyclooxygenase inhibitor (indomethacin) in 17 near-term fetal sheep. Catheters were placed in the left (LPA) and main pulmonary arteries, and an ultrasonic flow transducer was placed around the LPA to measure flow continuously. CGRP was injected directly into the LPA (mean 1.02 microgram/kg) before and after blockade, and responses to CGRP were statistically compared. Before blockade, CGRP increased LPA blood flow from 23 +/- 25 to 145 +/- 77 ml/min (means +/- SD), and these increases were significantly attenuated by CGRP(8-37) (n = 6; 91% inhibition), L-NNA (n = 6; 86% inhibition), and glibenclamide (n = 6; 69% inhibition). No significant changes were found with indomethacin (n = 6; 4% inhibition). Thus, in the fetal pulmonary circulation, CGRP increases pulmonary blood flow not only through its specific receptor but also, in part, through nitric oxide release and K(ATP) channel activation.

Sensitivity of myometrium to CGRP varies during mouse estrous cycle and in response to progesterone

Calcitonin gene-related peptide (CGRP) inhibits contractions of the myometrium. Isometric force measurements on myometrial strips were carried out to monitor the inhibitory capacity of CGRP in the myometrium during the estrous cycle and in response to estrogen and progesterone in ovariectomized mice. CGRP inhibition of KCl-induced contractions was lowest at estrus and significantly increased during metestrus and diestrus. Progesterone treatment of ovariectomized mice resulted in a significant increase in the responsiveness of the myometrium to CGRP. Expression of CGRP-receptor component protein (CGRP-RCP), a marker of CGRP-receptor expression, was quantitated by Western and Northern blot analyses. The levels of inhibition exerted by CGRP during the various stages of the estrous cycle and in response to steroid hormone treatment correlated with the protein levels of CGRP-RCP. The mRNA levels did not change significantly during the estrous cycle or in response to hormone treatment, indicating that the regulation of CGRP-RCP protein does not occur at the transcriptional level. CGRP had an inhibitory effect both when applied before the stimulus for contraction and when applied during a sustained contracture induced by KCl. This suggests that CGRP-induced generation of second messengers can influence late events in electro-/chemomechanical coupling and/or the contractile machinery directly.

Gene transfer of calcitonin gene-related peptide to cerebral arteries

Overexpression of calcitonin gene-related peptide (CGRP), an extremely potent vasodilator, to blood vessels is a possible strategy for prevention of vasospasm. We constructed an adenoviral vector that encodes prepro-CGRP (Adprepro-CGRP) and examined the effects of gene transfer on cultured cells and cerebral arteries. Transfection of Adprepro-CGRP to Cos-7 and NIH-3T3 cells increased CGRP-like immunoreactivity in media and produced an increase in cAMP in recipient cells. Five days after injection of Adprepro-CGRP into the cisterna magna of rabbits, the concentration of CGRP-like immunoreactivity increased by 93-fold in cerebrospinal fluid. In basilar artery, cAMP increased by 2.3-fold after Adprepro-CGRP compared with a control adenovirus. After transfection of Adprepro-CGRP, contraction of basilar artery in vitro to histamine and serotonin was attenuated, and relaxation to an inhibitor of cyclic nucleotide phosphodiesterase 3-isobutyl-1-methylxanthine was augmented compared with nontransduced arteries or arteries transfected with a control gene. Altered vascular responses were restored to normal by pretreatment with a CGRP(1) receptor antagonist CGRP-(8-37). Thus gene transfer of prepro-CGRP in vivo overexpresses CGRP in cerebrospinal fluid and perivascular tissues and modulates vascular tone. We speculate that this approach may be useful in prevention of vasospasm after subarachnoid hemorrhage.

Receptors mediating CGRP-induced relaxation in the rat isolated thoracic aorta and porcine isolated coronary artery differentiated by h(alpha) CGRP(8-37)

1 Receptors mediating CGRP-induced vasorelaxation were investigated in rat thoracic aorta and porcine left anterior descending (LAD) coronary artery and anterior interventricular artery (AIA), using CGRP agonists, homologues and the antagonist h(alpha) CGRP(8-37). 2 In the endothelium-intact rat aorta, h(alpha) CGRP, h(beta) CGRP, rat beta CGRP and human adrenomedullin caused relaxation with similar potencies. Compared with h(alpha) CGRP, rat amylin was about 25 fold less potent, while [Cys(ACM2,7)] h(alpha) CGRP and salmon calcitonin were at least 1000 fold weaker. 3 H(alpha) CGRP(8-37) (up to 10(-5) M) did not antagonize responses to h(alpha) CGRP, h(beta) CGRP or rat beta CGRP (apparent pKB <5). Peptidase inhibitors did not increase either the effect of h(alpha) CGRP or [Cys(ACM,2,7)] h(alpha) CGRP, while h(alpha) CGRP(8-37) remained inactive. Endothelium-dependent relaxation produced by h(alpha) CGRP was accompanied by increases in cyclic AMP and cyclic GMP, that were not inhibited by h(alpha) CGRP(8-37) (10(-5) M). 4 In porcine LAD and AIA, h(alpha) CGRP produced relaxation in an endothelium-independent manner. H(alpha) CGRP(8-37) competitively antagonized h(alpha) CGRP responses (pA2 6.3 and 6.7 (Schild slope 0.9+/-0.1, each), in LAD and AIA, respectively). In LAD artery, h(alpha) CGRP-induced relaxation was accompanied by increases in cyclic AMP that were inhibited by h(alpha) CGRP(8-37) (10(-7)-10(5 )). 5 In conclusion, the antagonist affinity for h(alpha) CGRP(8-37) in porcine coronary artery is consistent with a CGRP1 receptor, while the lack of h(alpha) CGRP(8-37) antagonism in rat aorta could suggest either a CGRP receptor different from CGRP1 and CGRP2 type, or a non-CGRP receptor.

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.

Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.

Effects of calcitonin gene-related peptide on vascular resistance in rats: role of sex steroids

It has been demonstrated in reflex-intact animals that the sensitivity to calcitonin gene-related peptide (CGRP) is increased during pregnancy and that this action is mediated by sex steroids but not by nitric oxide (NO). We assessed the effects of CGRP in the following groups of anesthetized ganglion-blocked rats: 1) pregnant, 2) ovariectomized, and 3) ovariectomized and treated with estradiol and progesterone. Changes in mean arterial pressure (MAP) were assessed after the administration of varying doses of CGRP. Decreases in MAP after CGRP administration were significantly greater in pregnant rats and ovariectomized rats administered sex steroids than in ovariectomized controls. The CGRP antagonist CGRP8-37 produced a pressor response of similar magnitude in both pregnant and ovariectomized rats. We also assessed the effects of CGRP and the modulating role of NO in the isolated uterine vascular bed preparation. CGRP reduced perfusion pressure to a greater degree in ovariectomized animals treated with sex steroids than in ovariectomized animals. This response was attenuated by pretreatment with an NO synthesis inhibitor. CGRP8-37 produced a similar increase in perfusion pressure in both groups. We conclude that 1) the increased vascular sensitivity observed during pregnancy or after treatment with sex steroids is in part mediated by NO, and 2) CGRP8-37 has a vasoconstrictor action of its own.

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.

A possible role of nitric oxide formation in the vasodilatation of rabbit ear artery induced by a topically applied Capsaicin analogue

Effects of topical application of a capsaicin analogue, nonylic acid vanillylamide (NVA, 0.032-10.0 mM) on the arterial diameter in the ear skin were examined in conscious rabbits using a precise dial caliper. In addition, the possibility of nitric oxide (NO) participating in a vasodilatation induced by low concentrations of NVA was tested by an NO synthase inhibitor. At the lowest concentration of NVA (0.032 mM), no significant change in the diameter was observed after external application of the NVA ointment. At concentrations of 0.32 mM or more, NVA produced a significant vasodilator response. However, at higher concentrations of 3.2 and 10.0 mM, -NVA induced substantial shrinkage in the arterial diameter and oedema formation, which was not affected by L-NAME (NG-nitro-L-arginine methyl ester, 3 mg/kg, i.v.), suggesting fluid leakage induced by oedema from the vessels might suppress the vasodilatation. Thus, the concentration-response curve for NVA was bell-shaped. NVA (0.32 mM)-induced vasodilatation was not significantly affected by atropine (1 mg/kg, i.v.) or propranolol (80 micrograms/kg, i.v.). However, the NVA-induced vasodilatation was completely suppressed by an NO synthase inhibitor, L-NAME (3 mg/kg, i.v.) which had no influence on the resting diameter, but not by an inactive stereoisomer, D-NAME (3 mg/kg, i.v.). These findings suggest that vanilloid receptor activation results in the release of sensory neuropeptides, which in turn stimulate the synthesis of endothelial NO which is responsible for the vasodilatation.

Effects of adrenomedullin and calcitonin gene-related peptide on contractions of the rat aorta and porcine coronary artery

1. Effects of adrenomedullin and alpha-calcitonin gene-related peptide (CGRP) on the contractions and cytosolic Ca2+ concentrations ([Ca2+]i) of the rat aorta and porcine coronary artery were investigated. Characteristics of the receptors mediating the effects of adrenomedullin and alpha-CGRP were also investigated. 2. Adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation in the rat aorta contracted with noradrenaline. The IC50 values for adrenomedullin and alpha-CGRP were 2.4 nM and 4.0 nM, respectively. The relaxant effects of these peptides were abolished by removal of the endothelium and significantly attenuated by an inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMMA, 100 microM), but not by a cyclo-oxygenase inhibitor, indomethacin (10 microM). 3. Adrenomedullin and alpha-CGRP increased the endothelial [Ca2+]i in the rat aorta with endothelium, whereas they did not change [Ca2+]i in the smooth muscle. 4. An antagonist of the CGRP1 receptor, CGRP (8-37), antagonized the relaxant effects of alpha-CGRP and the beta-isoform of CGRP (beta-CGRP) but not those of adrenomedullin in the rat aorta. 5. In the porcine coronary artery contracted with U46619, adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation with an IC50 of 27.6 and 4.1 nM, respectively. Removal of the endothelium altered neither the IC50 values nor the maximal relaxations induced by adrenomedullin or alpha-CGRP. When the artery was contracted with high K+ solution (72.7 mM), these peptides caused a small relaxation. 6. Adrenomedullin and alpha-CGRP increased cyclic AMP content and decreased the smooth muscle [Ca2+]i in the porcine coronary artery. 7. CGRP (8-37) significantly antagonized the relaxant effects of adrenomedullin and alpha-CGRP in the porcine coronary artery. However, it had little effect on the relaxations induced by the beta-isoform of CGRP (beta-CGRP). 8. These results suggest that in the rat aorta, adrenomedullin and alpha-CGRP increase the endothelial [Ca2+]i, activate nitric oxide synthase and release nitric oxide, without a direct inhibitory action on smooth muscle. In the porcine coronary artery, in contrast, adrenomedullin and alpha-CGRP directly act on smooth muscle, increase cyclic AMP content, decrease the smooth muscle [Ca2+]i and inhibit contraction. The rat aortic endothelium seems to express the CGRP receptor which is sensitive to alpha-CGRP, beta-CGRP and CGRP (8-37) and the adrenomedullin specific receptor. The porcine coronary smooth muscle, in contrast, seems to express two types of CGRP receptor; one of which is sensitive to alpha-CGRP, CGRP (8-37) and adrenomedullin and the other is sensitive only to beta-CGRP.

Calcitonin gene-related peptide relaxes rabbit iris dilator smooth muscle via cyclic AMP-dependent mechanisms: cross-talk between the sensory and sympathetic nervous systems

PURPOSE

The purpose of these studies is to determine whether or not cyclic AMP is involved in the relaxant action of calcitonin gene-related peptide (CGRP) in rabbit iris dilator muscle.

METHODS

Iris dilator muscle isolated from rabbit was used. Accumulation of cAMP and cGMP in the tissue extracts was measured by radioimmunoassay (RIA), IP3 production was measured by ion-exchange chromatography, and changes in tension were recorded isometrically.

RESULTS

CGRP, vasoactive intestinal peptide, prostaglandin E2, isoproterenol and forskolin (1 microM of each) increased cAMP accumulation by 136, 256, 78, 141 and 315%, respectively. CGRP dose-dependently increased cAMP accumulation (EC50 = 5.25 nM), inhibited IP3 production (EC50 = 5.4 nM) and induced relaxation (EC50 = 10 nM) in muscle precontracted with norepinephrine (NE) (10 microM). Prostaglandin E2, isoproterenol and forskolin also induced relaxation. CGRP stimulated cAMP formation either in the presence or absence of 3-isobutyl-1-methylxanthine (IBMX), a cAMP phosphodiesterase inhibitor, in a time- and concentration-dependent manner. The neuropeptide had no effect on cGMP accumulation. CGRP (8-37), a CGRP receptor antagonist, reversed the relaxant action of the neuropeptide and inhibited CGRP-induced cAMP accumulation in a concentration-dependent manner (IC50 = 12.5 nM). 2',5'-dideoxyadenosine (DDA), a specific adenylate cyclase inhibitor, significantly reduced the inhibitory actions of CGRP on NE-induced contraction and IP3 production and inhibited CGRP-induced cAMP accumulation in a concentration-dependent manner (IC50 = 6.9 nM).

CONCLUSIONS

These results strongly suggest that cAMP mediates the relaxant action of CGRP in rabbit iris dilator. The mechanism of cAMP inhibition of NE-induced IP3 production and contraction is unclear. Modulation of alpha 1-adrenergic function in the iris dilator by CGRP-induced cAMP formation is yet another example of cross-talk between the cAMP and IP3-Ca2+ second messenger systems, it demonstrates a cross-talk between the sympathetic and sensory nervous systems. CGRP-containing sensory nerve fibers could play an important role in regulation of smooth muscle function in the iris-ciliary body.

Innervation of the human middle meningeal artery: immunohistochemistry, ultrastructure, and role of endothelium for vasomotility

The majority of nerve fibers in the middle meningeal artery and branching arterioles are sympathetic, storing norepinephrine and neuropeptide Y (NPY). A sparse supply of fibers contain acetylcholinesterase activity and immunoreactivity toward vasoactive intestinal peptide (VIP), peptidine histidine methionine (PHM), and calcitonin gene-related peptide (CGRP). Only few substance P and neuropeptide K immunoreactive fibers are noted. Electronmicroscopy shows axons and terminals at the adventitial medial border of the human middle meningeal artery, with a fairly large distance to the smooth muscle cells (>500 nM). Several axon profiles contain vesicles of different types, including putative sensory profiles. The perivascularly stored signal substances, norepinephrine and NPY induced vasoconstrictor. Relaxations were induced by acetylcholine and substance P, and these were significantly reduced in arteries without endothelium, while the responses to norepinephrine, NPY, VIP, PHM, and CGRP were not changed by endothelium removal. Blockade experiments showed that the vasomotor responses to norepinephrine were blocked by prazosin, to NPY by BIBP 3226, acetylcholine by atropin, substance P by RP 67580, and the human alpha-CGRP response by human alpha-CGRP(8-37).

Developmental changes in binding sites and reactivity for CGRP and VIP in porcine pulmonary arteries

During postnatal adaptation pulmonary arteries dilate. CGRP and VIP are pulmonary vasodilators. In this report, porcine lungs from newborn to adult were studied. Radiolabeled ligand binding and autoradiography showed CGRP binding sites on the endothelium of pulmonary arteries and veins, which increased postnatally, and VIP binding sites on smooth muscle, which decreased. Isolated conduit arteries relaxed normally (initially endothelium dependent) in response to CGRP from birth. VIP first caused relaxation at 10 days and was endothelium dependent. Age-related changes in receptor binding density were not always reflected in an appropriate alteration in pharmacological response.

The antiproliferative effects of calcitonin gene-related peptide in different passages of cultured vascular smooth muscle cells

Previously our laboratory showed that calcitonin gene-related peptide (CGRP) is released from perivascular nerves exposed to endotoxin or inflammatory mediators bradykinin and prostaglandins. CGRP contributes significantly to the vasodilation of inflammation and septic shock. Another potential action of CGRP is inhibition of vascular smooth muscle cell (VSMC) growth, which could serve to counterbalance the stimulatory effects of IL-1 and TNF on VSMC proliferation. VSMCs from rabbit and rat aorta (in the second and fifth passages) were plated at 100,000 cells/well in 24-well trays in 10% fetal bovine serum (FBS) for 24 h, incubated for an additional 24 h without FBS, and then exposed to 2.5% FBS for 24 h in the presence or absence of CGRP. 3H-thymidine incorporation was used to measure DNA synthesis and proliferation. CGRP caused significant inhibition of 3H-thymidine incorporation, which correlated with elevations of cAMP in both rat and rabbit aortic VSMCs. Interestingly, the responses of both the elevation of cAMP and the inhibition of DNA synthesis became larger in VSMCs with an increasing number of passages. The data suggest that the CGRP, released during vascular inflammation, may serve to inhibit the proliferation of VSMCs, thus limiting the growth of atheromatous lesions.

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+.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Atrial natriuretic peptides increase calcitonin gene-related peptide within human circulation

Long-acting natriuretic peptide (LANP), vessel dilator, and atrial natriuretic factor (ANF) (each infused at 100 ng/kg body weight [BW].min for 60 minutes) increased the circulating concentration of calcitonin gene-related peptide (CGRP) threefold to fourfold in 30 healthy humans. Within 30 minutes of stopping ANF infusion, the CGRP circulating concentration had returned to preinfusion levels, whereas its increase secondary to the other atrial peptides was still significant 2 to 3 hours after cessation of their infusions. There was a 50% decreased excretion (P < .001) of CGRP into the urine secondary to LANP and vessel dilator, which correlated with the increase of CGRP in the circulation. The ANF-induced 50% decreased CGRP excretion occurred after the circulating concentration of CGRP had returned to preinfusion levels. Kaliuretic peptide did not affect CGRP circulating concentration or excretion into urine. These data suggest that LANP and vessel dilator inhibit the metabolic breakdown of CGRP as part of their mechanism of increasing CGRP in plasma, whereas the ANF effect of increasing CGRP in plasma appears to be secondary to stimulating the release of CGRP.

Calcitonin gene-related peptide receptor in human placental syncytiotrophoblast brush-border and basal plasma membranes

Minerals, such as calcium and potassium, are essential for fetal development, but their transplacental transport, and in particular, the effect of hormones on this process has not been extensively studied. Human alpha-calcitonin gene-related peptide (h alpha CGRP), a hormone constituted of 37 amino acids, is obtained by the alternative splicing of the mRNA from the calcitonin gene, and could be implicated in placental ion transport. In order to study the presence of this receptor, brush-border and basal plasma membranes were purified, and membrane binding studies were conducted using [125I]h alpha CGRP. The initiation of binding of [125I]h alpha CGRP to both membranes was rapid and reached maximal value after 10 min of incubation at 37 degrees C. Scratchard analysis revealed single-affinity binding sites for h alpha CGRP with Kd equal to 4412.45 +/- 604.81 pM and 2673.24 +/- 552.51 pM for brush-border and basal plasma membranes, respectively, which were significantly different. Moreover, the maximal number of receptors was significantly different (P < 0.001) in both membranes, with Bmax of 627.94 +/- 31.40 fmol/mg protein for brush-border membranes and 343.70 +/- 43.52 fmol/mg protein in basal-plasma membranes. Competitive displacement of [125I]h alpha CGRP with other ligands showed the following potencies; h alpha CGRP approximately h beta CGRP approximately Cys (acm)2,7 CGRP > CGRP (8-37), but no competition was observed with human and salmon calcitonin. Half-maximal displacement for human alpha- and beta CGRP was reached at approximately 10(-10)M for brush-border and basal-plasma membranes. alpha- and beta CGRP, and their fragment and analogue, stimulated cyclic AMP production in placental homogenate ranging from 143-163 per cent. Thus, our results show the presence of CGRP-specific receptors in both the syncytiotrophoblast membranes of human placenta. The role(s) of this related peptide in placenta remains to be investigated.

Differential effects of guanine nucleotides on [125I]-hCGRP(8-37) binding to porcine lung and human neuroblastoma cell membranes

Calcitonin gene-related peptide (CGRP) mediates its effects by binding to specific receptors which are positively coupled to adenylyl cyclase. CGRP(8-37), a CGRP fragment devoid of the N-terminal region, was shown to be a competitive CGRP receptor antagonist. Only a limited amount of data exists on the usefulness of this ligand in studying CGRP receptors. In the present study, we used [125I]-hCGRP(8-37) to characterize CGRP receptors in porcine lung and human neuroblastoma cell (SK-N-MC) membranes. [125I]-hCGRP(8-37) displayed specific and high affinity binding in both membrane preparations. Displacement studies using [125I]-hCGRP(8-37) and the agonist CGRP revealed the presence of high and low affinity CGRP binding sites in SK-N-MC cell and porcine lung membranes. Addition of guanylimidodiphosphate [Gpp(NH)p] shifted the competition curve to the right and changed the two affinity states of the receptor to a single affinity in SK-N-MC cell membranes. On the other hand, in porcine lung membranes, the whole competition curve was shifted to the right while maintaining the two affinity states. Thus, our data indicate that the new radioligand [125I]-hCGRP(8-37) is a useful tool for characterizing CGRP receptors and their coupling to guanine nucleotide binding proteins.

Calcitonin gene-related peptide is a depressor in NG-nitro-L-arginine methyl ester-induced hypertension during pregnancy

Inhibition of nitric oxide production with NG-nitro-L-arginine methyl ester (L-NAME) increases blood pressure and fetal mortality in pregnant rats. We previously reported that administration of calcitonin gene-related peptide (CGRP) reduces the blood pressure and fetal death produced by L-NAME. To determine the hemodynamic role of endogenous CGRP in this setting, CGRP8-37, a CGRP receptor antagonist, was used. In addition, CGRP mRNA and peptide levels were determined in dorsal root ganglia. L-NAME or control rats had intravenous (for drug administration) and arterial (for continuous mean blood pressure monitoring) catheters surgically placed and were studied in the conscious unrestrained state. Baseline blood pressure was higher in the L-NAME than the control rats on days 19, 20, and 21 or pregnancy and postpartum day 1. Vehicle administration did not change blood pressure in any group, and CGRP8-37 (100 micrograms) did not change blood pressure in control groups. However, CGRP8-37 administration to the L-NAME rats further increased blood pressure (P < .05) on days 19 (8 +/- 1), 20 (12 +/- 2), and 21 (7 +/- 1) of gestation but was without effect on postpartum day 1. Furthermore, CGRP mRNA or peptide levels in dorsal root ganglia were not different between the L-NAME and control rats at any of the time points studied. These data indicate that in experimental preeclampsia, CGRP is playing a compensatory vasodilator role to attenuate the elevated blood pressure. The mechanism of this effect appears to be an enhanced vascular responsiveness to CGRP that is attenuated after the birth of pups.

The calcitonin gene-related peptide activates both cAMP and NO pathways to induce relaxation of circular smooth muscle cells of guinea-pig ileum

The direct effects and the intracellular pathways of rCGRP were investigated on smooth muscle cells (SMC) isolated by enzymatic digestion from the circular and longitudinal layers of guinea-pig ileum. In circular SMC, rCGRP inhibited CCK8-induced contraction in a concentration-dependent manner (Cmax = 100 microM and EC50 = 0.7 +/- 0.4 nM). Preincubation of SMC with 1 microM Rp-cAMPs, a cAMP antagonist, abolished the relaxing effect of rCGRP; moreover, preincubation of SMC with 100 microM L-NAME, an inhibitor of NOS, inhibited the relaxing effect of rCGRP, hCGRP(8-37), a selective antagonist of rCGRP receptors, inhibited the rCGRP-induced relaxation in a concentration dependent manner whereas the vasoactive intestinal polypeptide (VIP) antagonist had no significant effect. In longitudinal SMC, rCGRP-induced relaxation was abolished by Rp-cAMPs, whereas L-NAME had no effect. In conclusion, rCGRP triggers different intracellular pathways to induce relaxation of circular or longitudinal intestinal SMC; cAMP is involved in cells from both layers while nitric oxide (NO) is involved only in relaxation of circular SMC.

Calcitonin gene-related peptide inhibits human platelet aggregation

Calcitonin gene-related peptide (CGRP) is a potent vasodilator in humans. CGRP receptors have also been found in various tissues other than blood vessels, such as the central nervous system, kidney, and heart. However, little is known about the effects of CGRP on human platelets. We investigated the effect of CGRP (human alpha type) on platelet aggregation in 21 healthy subjects (9 men and 12 women, mean age 54.6 years). CGRP inhibited platelet aggregation in vitro in 19 of the subjects (90.5%) in a dose-dependent manner with 50% inhibitory doses of 1.6 mumol/L and 1.1 mumol/L for aggregation induced by epinephrine and collagen, respectively. 125I-labeled CGRP bound specifically to intact platelets. The dissociation constant (Kd) was 61.9 +/- 17.7 pmol and the maximum number of binding sites (Bmax) was 5.4 +/- 3.9 pmol/10(9) platelets. The CGRP analogue (8-37)CGRP, but not calcitonin, inhibited the binding of 125I-CGRP to platelets. CGRP (5 mumol/L), but not (8-37)CGRP or calcitonin, increased the platelet cyclic AMP (cAMP) concentration by 31.7 +/- 3.6%. Thus, CGRP inhibits platelet aggregation via a specific receptor and by increasing the platelet cAMP concentration. CGRP may play a role in the modulation of platelet function in humans.

Calcitonin gene-related peptide is released from capsaicin-sensitive nerve fibres and induces vasodilatation of human cerebral arteries concomitant with activation of adenylyl cyclase

The vasomotor effects of calcitonin gene-related peptide (CGRP) analogues have been studied in circular segments of fresh human cerebral arteries obtained at neurosurgical operations using a sensitive in vitro system. Human alpha-CGRP, human beta-CGRP, rat alpha-CGRP and rat beta-CGRP induced strong and potent relaxation of precontracted circular vessel segments. The Imax (maximum relaxant effect) to human calcitonin was low and the pD2 (concentration for half maximum effect) 7.7 was much lower than that of CGRP. The CGRP-1, antagonist human alpha-CGRP8-37 blocked the response to human alpha-CGRP but not to human beta-CGRP, while the putative antagonist [Tyr]CGRP28-37 did not. Capsaicin (10(-15)-10(-8)M) caused relaxation of the cerebral arteries by 22% of precontraction. Pre-treatment with 10(-6)M human alpha-CGRP8-37 inhibited this relaxation. Human alpha-CGRP increased the cyclic AMP content of human cerebral arteries in a concentration-dependent manner. This increase in adenylyl cyclase activity was blocked by human alpha-CGRP8-37. The results suggest that CGRP-1 receptors coupled to adenylyl cyclase are present in human cerebral arteries.

Substance P and calcitonin gene-related peptide in the chicken skin: distribution and cardiovascular effects

A short vasodilatation but no plasma extravasation could be induced by antidromic stimulation of peripheral nerves in the chicken skin. Since in mammalian species the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) are involved in this mechanism, the distribution and the cardiovascular effect of these peptides were investigated in the chicken. In the skin, SP- and CGRP-immunoreactivity was found co-localized in the epidermis and dermis. On blood vessels, however, SP positive but CGRP negative nerve rfibres were observed. Systemic (i.v.) and local close arterial injection of SP produced dose-dependent cutaneous vasodilatation with threshold doses of 6.5 pmol/kg or 1 pmol, respectively. Neurokinin A and acetylcholine were about 20 to 50-fold less effective, when injected close arterially. Systemic injection of SP (5-1800 pmol/kg) dose-dependently evoked a short fall in blood pressure which was followed by a longer lasting pressor response. CGRP up to 800 pmol/kg did not change blood pressure but produced a pronounced tachycardia. Close arterial injection of CGRP resulted in variable bi- or triphasic vascular responses which consisted of vasodilatations and also vasoconstriction with thresholds between 0.25 and 65 pmol. The data also indicate that in the chicken, SP, and to a lesser extent CGRP, can be involved in antidromic vasodilatation.

A cDNA encoding the calcitonin gene-related peptide type 1 receptor

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse biological effects including potent vasodilator activity. We report here the cloning of a complementary DNA (cDNA) encoding a human CGRP1 receptor, which shares significant peptide sequence homology with the human calcitonin receptor, a member of the G-protein-coupled receptor superfamily. Northern blot analysis revealed that the messenger RNA for this receptor is predominantly expressed in the lung and heart. In situ studies showed specific localization of the receptor mRNA to alveolar cells in the lung and to cardiac myocytes in the heart. Stable expression of the cDNA in human embryonic kidney 293 (HEK 293) cells produced specific, high affinity binding sites for CGRP that displayed pharmacological and functional properties very similar to native human CGRP1 receptor. Exposure of these cells to CGRP resulted in a 60-fold increase in cAMP production, which was inhibited in a competitive manner by the CGRP1 receptor antagonist, CGRP-(8-37).