Inhibition of periarterial nerve stimulation-induced vasodilation of the mesenteric arterial bed by CGRP (8-37) and CGRP receptor desensitization

Elevated plasma levels of calcitonin gene-related peptide in individuals with rosacea: A cross-sectional case-control study

BACKGROUND

Understanding the role of calcitonin gene-related peptide (CGRP) in the pathogenesis of rosacea might provide new therapeutic avenues for individuals with this disease.

OBJECTIVE

To compare plasma levels of CGRP between individuals with rosacea and healthy controls.

METHODS

In this cross-sectional case-control study conducted in Copenhagen, Denmark, we collected blood samples from the antecubital vein from adults with rosacea and from healthy controls.

RESULTS

We enrolled 123 individuals with rosacea and 68 healthy controls. After adjusting for age and sex, plasma levels of CGRP were significantly higher in individuals with rosacea (mean, 95% confidence interval: 140.21 pmol/L, 128.50-151.92 pmol/L), compared with controls (110.77 pmol/L, 99.91-120.14 pmol/L, p = 0.002). Plasma levels of CGRP were not affected by age, sex, BMI, concomitant migraine, rosacea sub- or phenotype, concomitant disease or current treatment.

LIMITATIONS

Participants were not age-, sex- and BMI-matched.

CONCLUSIONS AND RELEVANCE

Elevated plasma levels of CGRP in individuals with rosacea suggest a role of CGRP in the pathogenesis of rosacea. Targeting CGRP signalling might hold therapeutic promise in people affected by this disease.

CLINICALTRIALS

GOV LISTING

NCT03872050.

Erenumab for Treatment of Persistent Erythema and Flushing in Rosacea: A Nonrandomized Controlled Trial

Importance

Treatment of erythema and flushing in rosacea is challenging. Calcitonin gene-related peptide (CGRP) has been associated with the pathogenesis of rosacea, raising the possibility that inhibition of the CGRP pathway might improve certain features of the disease.

Objective

To examine the effectiveness, tolerability, and safety of erenumab, an anti-CGRP-receptor monoclonal antibody, for the treatment of rosacea-associated erythema and flushing.

Design, Setting, and Participants

This single-center, open-label, single-group, nonrandomized controlled trial was conducted between June 9, 2020, and May 11, 2021. Eligible participants included adults with rosacea with at least 15 days of either moderate to severe erythema and/or moderate to extreme flushing. No concomitant rosacea treatment was allowed throughout the study period. Visits took place at the Danish Headache Center, Copenhagen University Hospital, Rigshospitalet in Copenhagen, Denmark. Participants received 140 mg of erenumab subcutaneously every 4 weeks for 12 weeks. A safety follow-up visit was performed at week 20. Data analysis occurred from January 2023 to January 2024.

Intervention

140 mg of erenumab every 4 weeks for 12 weeks.

Main Outcomes and Measures

The primary outcome was mean change in the number of days with moderate to extreme flushing during weeks 9 through 12, compared with the 4-week run-in period (baseline). The mean change in number of days with moderate to severe erythema was a secondary outcome. Adverse events were recorded for participants who received at least 1 dose of erenumab. Differences in means were calculated with a paired t test.

Results

A total of 30 participants (mean [SD] age, 38.8 [13.1] years; 23 female [77%]; 7 male [23%]) were included, of whom 27 completed the 12-week study. The mean (SD) number of days with moderate to extreme flushing was reduced by -6.9 days (95% CI, -10.4 to -3.4 days; P < .001) from 23.6 (5.8) days at baseline. The mean (SD) number of days with moderate to severe erythema was reduced by -8.1 days (95% CI, -12.5 to -3.7 days; P < .001) from 15.2 (9.1) days at baseline. Adverse events included transient mild to moderate constipation (10 participants [33%]), transient worsening of flushing (4 participants [13%]), bloating (3 participants [10%]), and upper respiratory tract infections (3 participants [10%]), consistent with previous data. One participant discontinued the study due to a serious adverse event (hospital admission due to gallstones deemed unrelated to the study), and 2 participants withdrew consent due to lack of time.

Conclusions and Relevance

These findings suggest that erenumab might be effective in reducing rosacea-associated flushing and chronic erythema (participants generally tolerated the treatment well, which was consistent with previous data), and that CGRP-receptor inhibition holds potential in the treatment of erythema and flushing associated with rosacea. Larger randomized clinical trials are needed to confirm this finding.

Trial Registration

ClinicalTrials.gov Identifier: NCT04419259.

Serotonergic Modulation of Neurovascular Transmission: A Focus on Prejunctional 5-HT Receptors/Mechanisms

5-Hydroxytryptamine (5-HT), or serotonin, plays a crucial role as a neuromodulator and/or neurotransmitter of several nervous system functions. Its actions are complex, and depend on multiple factors, including the type of effector or receptor activated. Briefly, 5-HT can activate: (i) metabotropic (G-protein-coupled) receptors to promote inhibition (5-HT₁, 5-HT₅) or activation (5-HT₄, 5-HT₆, 5-HT₇) of adenylate cyclase, as well as activation (5-HT₂) of phospholipase C; and (ii) ionotropic receptor (5-HT₃), a ligand-gated Na⁺/K⁺ channel. Regarding blood pressure regulation (and beyond the intricacy of central 5-HT effects), this monoamine also exerts direct postjunctional (on vascular smooth muscle and endothelium) or indirect prejunctional (on autonomic and sensory perivascular nerves) effects. At the prejunctional level, 5-HT can facilitate or preclude the release of autonomic (e.g., noradrenaline and acetylcholine) or sensory (e.g., calcitonin gene-related peptide) neurotransmitters facilitating hypertensive or hypotensive effects. Hence, we cannot formulate a specific impact of 5-HT on blood pressure level, since an increase or decrease in neurotransmitter release would be favoured, depending on the type of prejunctional receptor involved. This review summarizes and discusses the current knowledge on the prejunctional mechanisms involved in blood pressure regulation by 5-HT and its impact on some vascular-related diseases.

Electrical neuromodulation therapy for inflammatory bowel disease

Inflammatory bowel disease (IBD) is an inflammatory disease of the gastrointestinal (GI) tract. It has financial and quality of life impact on patients. Although there has been a significant advancement in treatments, a considerable number of patients do not respond to it or have severe side effects. Therapeutic approaches such as electrical neuromodulation are being investigated to provide alternate options. Although bioelectric neuromodulation technology has evolved significantly in the last decade, sacral nerve stimulation (SNS) for fecal incontinence remains the only neuromodulation protocol commonly utilized use for GI disease. For IBD treatment, several electrical neuromodulation techniques have been studied, such as vagus NS, SNS, and tibial NS. Several animal and clinical experiments were conducted to study the effectiveness, with encouraging results. The precise underlying mechanisms of action for electrical neuromodulation are unclear, but this modality appears to be promising. Randomized control trials are required to investigate the efficacy of intrinsic processes. In this review, we will discuss the electrical modulation therapy for the IBD and the data pertaining to it.

Role of TRP ion channels in cerebral circulation and neurovascular communication

The dynamic regulation of blood flow is essential for meeting the high metabolic demands of the brain and maintaining brain function. Cerebral blood flow is regulated primarily by 1) the intrinsic mechanisms that determine vascular contractility and 2) signals from neurons and astrocytes that alter vascular contractility. Stimuli from neurons and astrocytes can also initiate a signaling cascade in the brain capillary endothelium to increase regional blood flow. Recent studies provide evidence that TRP channels in endothelial cells, smooth muscle cells, neurons, astrocytes, and perivascular nerves control cerebrovascular contractility and cerebral blood flow. TRP channels exert their functional effects either through cell membrane depolarization or by serving as a Ca2+ influx pathway. Endothelial cells and astrocytes also maintain the integrity of the blood-brain barrier. Both endothelial cells and astrocytes express TRP channels, and an increase in endothelial TRP channel activity has been linked with a disrupted endothelial barrier function. Therefore, TRP channels can play a potentially important role in regulating blood-brain barrier integrity. Here, we review the regulation of cerebrovascular contractility by TRP channels under healthy and disease conditions and their potential roles in maintaining blood-brain barrier function.

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

Sympathetic and Sensory-Motor Nerves in Peripheral Small Arteries

Small arteries, which play important roles in controlling blood flow, blood pressure, and capillary pressure, are under nervous influence. Their innervation is predominantly sympathetic and sensory motor in nature, and while some arteries are densely innervated, others are only sparsely so. Innervation of small arteries is a key mechanism in regulating vascular resistance. In the second half of the previous century, the physiology and pharmacology of this innervation were very actively investigated. In the past 10-20 yr, the activity in this field was more limited. With this review we highlight what has been learned during recent years with respect to development of small arteries and their innervation, some aspects of excitation-release coupling, interaction between sympathetic and sensory-motor nerves, cross talk between endothelium and vascular nerves, and some aspects of their role in vascular inflammation and hypertension. We also highlight what remains to be investigated to further increase our understanding of this fundamental aspect of vascular physiology.

Is calcitonin gene-related peptide a modulator of menopausal vasomotor symptoms?

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed in the central and peripheral nervous systems, which is known as a potent vasodilator. Postmenopausal women who experience hot flushes have high levels of plasma CGRP, suggesting its involvement in menopausal vasomotor symptoms.

METHODS

In this review, we describe the biochemical aspects of CGRP and its effects associated with deficiencies of sexual hormones on skin temperature, vasodilatation, and sweating as well as the possible peripheral and central mechanisms involved in these events.

RESULTS

Several studies have shown that the effects of CGRP on increasing skin temperature and inducing vasodilatation are potentiated by a deficiency of sex hormones, a common condition of postmenopausal women. Additionally, the medial preoptic area of the hypothalamus, involved in thermoregulation, contains over 25-fold more CGRP-immunoreactive cells in female rodents compared with male rodents, reinforcing the role of female sex hormones on the action of CGRP. Some studies suggest that ovarian hormone deficiency decreases circulating endogenous CGRP, inducing an upregulation of CGRP receptors. Consequently, the high CGRP receptor density, especially in blood vessels, amplifies the stimulatory effects of this neuropeptide to raise skin temperature in postmenopausal women during hot flushes.

CONCLUSIONS

The duration of the perception of each hot flush in a woman is brief, while local reddening after intradermal administration of α-CGRP persists for 1 to 6 h. This contrast remains unclear.

Heteroreceptors Modulating CGRP Release at Neurovascular Junction: Potential Therapeutic Implications on Some Vascular-Related Diseases

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide belonging to the calcitonin gene peptide superfamily. CGRP is a potent vasodilator with potential therapeutic usefulness for treating vascular-related disease. This peptide is primarily located on C- and Aδ-fibers, which have extensive perivascular presence and a dual sensory-efferent function. Although CGRP has two major isoforms (α-CGRP and β-CGRP), the α-CGRP is the isoform related to vascular actions. Release of CGRP from afferent perivascular nerve terminals has been shown to result in vasodilatation, an effect mediated by at least one receptor (the CGRP receptor). This receptor is an atypical G-protein coupled receptor (GPCR) composed of three functional proteins: (i) the calcitonin receptor-like receptor (CRLR; a seven-transmembrane protein), (ii) the activity-modifying protein type 1 (RAMP1), and (iii) a receptor component protein (RCP). Although under physiological conditions, CGRP seems not to play an important role in vascular tone regulation, this peptide has been strongly related as a key player in migraine and other vascular-related disorders (e.g., hypertension and preeclampsia). The present review aims at providing an overview on the role of sensory fibers and CGRP release on the modulation of vascular tone.

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.

TRPV channels and vascular function

Transient receptor potential channels, of the vanilloid subtype (TRPV), act as sensory mediators, being activated by endogenous ligands, heat, mechanical and osmotic stress. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells, as well as in peri-vascular nerves. Their varied distribution and polymodal activation properties make them ideally suited to a role in modulating vascular function, perceiving and responding to local environmental changes. In endothelial cells, TRPV1 is activated by endocannabinoids, TRPV3 by dietary agonists and TRPV4 by shear stress, epoxyeicosatrienoic acids (EETs) and downstream of Gq-coupled receptor activation. Upon activation, these channels contribute to vasodilation via nitric oxide, prostacyclin and intermediate/small conductance potassium channel-dependent pathways. In smooth muscle, TRPV4 is activated by endothelial-derived EETs, leading to large conductance potassium channel activation and smooth muscle hyperpolarization. Conversely, smooth muscle TRPV2 channels contribute to global calcium entry and may aid constriction. TRPV1 and TRPV4 are expressed in sensory nerves and can cause vasodilation through calcitonin gene-related peptide and substance P release as well as mediating vascular function via the baroreceptor reflex (TRPV1) or via increasing sympathetic outflow during osmotic stress (TRPV4). Thus, TRPV channels play important roles in the regulation of normal and pathological cellular function in the vasculature.

Activation of 5-HT1B receptors inhibits the vasodepressor sensory CGRPergic outflow in pithed rats

The importance of calcitonin gene-related peptide (CGRP) in the regulation of vascular tone has been widely documented. Indeed, stimulation of the perivascular sensory outflow in pithed rats results in vasodepressor responses, which are mediated by CGRP release. These vasodepressor responses are inhibited by clonidine via prejunctional alpha(2A/2C)-adrenoceptors, but no study has yet reported the role of prejunctional 5-hydroxytryptamine (5-HT) receptors in this experimental model. Since activation of prejunctional 5-HT(1) receptors results in inhibition of neurotransmitter release, this study sets out to investigate as an initial approach the role of 5-HT(1B) receptors in the inhibition of the vasodepressor sensory outflow in pithed rats. Male Wistar pithed rats were pretreated with hexamethonium (2mg/kg.min) followed by i.v. continuous infusions of methoxamine (20 microg/kg min), and then by saline (0.02 ml/min) or CP-93,129 (a rodent 5-HT(1B) receptor agonist; 0.1, 1 and 10 microg/kg min). Under these conditions, electrical stimulation (0.56-5.6 Hz; 50 V and 2 ms) of the spinal cord (T(9)-T(12)) resulted in frequency-dependent decreases in diastolic blood pressure. The infusions of CP-93,129, as compared to those of saline, inhibited the vasodepressor responses induced by electrical stimulation without affecting those to i.v. bolus injections of exogenous alpha-CGRP (0.1, 0.18, 0.31, 0.56 and 1 microg/kg). This inhibition by CP-93,129 was abolished by the antagonists GR127935 (5-HT(1B/1D)) or SB224289 (5-HT(1B)), but not by BRL15572 (5-HT(1D)). The above results suggest that CP-93,129-induced inhibition of the vasodepressor (perivascular) sensory outflow in pithed rats is mainly mediated by activation of prejunctional 5-HT(1B) receptors.

Royal jelly ameliorates insulin resistance in fructose-drinking rats

Royal jelly (RJ) is known to contain excellent nutrition and a variety of biological activities. The present study was designed to investigate the effects of RJ on insulin resistance (hyperinsulinemia) in fructose-drinking rats (FDR; insulin resistance animal model). Male Wistar rats (6 weeks old) received 15% fructose solution in drinking water for 8 weeks. FDR showed significant increases in plasma levels of insulin and triglyceride, Homeostasis Model Assessment ratio (HOMA-R, an index of insulin resistance), and systolic blood pressure, but not blood glucose levels, when compared with control rats. RJ (100, 300 mg/kg, p.o.) treatment for 8 weeks significantly decreased the plasma levels of insulin and triglyceride, HOMA-R, without affecting blood glucose or total cholesterol levels and tended to lower systolic blood pressure. In isolated and perfused mesenteric vascular beds of FDR, RJ treatment resulted in a significant reduction in sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS) and tended to increase the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with those in untreated FDR. However, RJ treatment did not significantly affect norepinephrine-induced vasoconstriction or CGRP-induced vasodilation. These results suggest that RJ could be an effective functional food to prevent insulin resistance associated with the development of hypertension.

Lafutidine facilitates calcitonin gene-related peptide (CGRP) nerve-mediated vasodilation via vanilloid-1 receptors in rat mesenteric resistance arteries

Lafutidine is a histamine H(2)-receptor antagonist with gastric antisecretory and gastroprotective activity associated with activation of capsaicin-sensitive nerves. The present study examined the effect of lafutidine on neurotransmission of capsaicin-sensitive calcitonin gene-related peptide (CGRP)-containing vasodilator nerves (CGRPergic nerves) in rat mesenteric resistance arteries. Rat mesenteric vascular beds were perfused with Krebs solution and vascular endothelium was removed by 30-s perfusion with sodium deoxycholate. In preparations preconstricted by continuous perfusion of methoxamine (alpha(1) adrenoceptor agonist), perfusion of lafutidine (0.1 - 10 microM) concentration-dependently augmented vasodilation induced by the periarterial nerve stimulation (PNS, 1 Hz) without affecting vasodilation induced by exogenous CGRP (10 pmol) injection. Perfusion of famotidine (H(2)-receptor antagonist, 1 - 100 microM) had no effect on either PNS-induced or CGRP-induced vasodilation. Perfusion of lafutidine concentration-dependently augmented vasodilation induced by a bolus injection of capsaicin (vanilloid-1 receptor agonist, 30 pmol). The presence of a vanilloid-1 receptor antagonist, ruthenium red (10 microM) or capsazepine (5 microM), abolished capsaicin-induced vasodilation and significantly decreased the PNS-induced vasodilation. The decreased PNS-induced vasodilation by ruthenium red or capsazepine was not affected by perfusion of lafutidine. These results suggest that lafutidine facilitates CGRP nerve-mediated vasodilation by modulating the function of presynaptic vanilloid-1 receptors located in CGRPergic nerves.

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).

Adrenomedullin facilitates reinnervation of phenol-injured perivascular nerves in the rat mesenteric resistance artery

Our previous report showed that innervation of calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-containing nerves in rat mesenteric resistance arteries was markedly reduced by topical application of phenol, and that nerve growth factor (NGF) facilitates the reinnervation of both nerves. We also demonstrated that a CGRP superfamily peptide, adrenomedullin, is distributed in perivascular nerves of rat mesenteric resistance arteries. In the present study, we investigated the influence of adrenomedullin on the reinnervation of mesenteric perivascular nerves following topical phenol treatment. Under pentobarbital-Na anesthesia, 8-week-old Wistar rats underwent in vivo topical application of phenol (10% phenol in 90% ethanol) to the superior mesenteric artery proximal to the bifurcation of the abdominal aorta. After the treatment, the animals were subjected to immunohistochemistry of the third branch of small arteries proximal to the intestine and to vascular responsiveness testing on day 7. Topical phenol treatment caused marked reduction of the density of NPY-like immunoreactive (LI)- and CGRP-LI nerve fibers in the arteries. Adrenomedullin (360 or 1000 ng/h) or NGF (250 ng/h), which was administered intraperitoneally for 7 days using an osmotic mini-pump immediately after topical phenol treatment, significantly increased the density of CGRP-LI- and NPY-LI nerve fibers compared with saline. Treatment with adrenomedullin (1000 ng/h) or NGF restored adrenergic nerve-mediated vasoconstriction and CGRP nerve-mediated vasodilation in the perfused mesenteric artery treated topically with phenol. These results suggest that adrenomedullin, like NGF, has a facilitatory effect on the reinnervation of perivascular nerves.

Innervation and functional changes in mesenteric perivascular calcitonin gene-related peptide- and neuropeptide Y-containing nerves following topical phenol treatment

We have previously shown that age-related reduction of innervation and function in mesenteric perivascular calcitonin gene-related peptide-containing vasodilator nerves takes place in spontaneously hypertensive rats. The present study was performed to investigate innervation and functional changes in perivascular calcitonin gene-related peptide- and adrenergic neuropeptide Y-containing nerves after topical treatment with phenol, which damages nerve fibers, around the rat superior mesenteric artery. Under pentobarbital-Na anesthesia, 8-week-old Wistar rats underwent in vivo topical application of phenol (10% phenol in 90% ethanol) or saline (sham rats) to the superior mesenteric artery proximal to the bifurcation of the abdominal aorta. After the treatment, the animals were subjected to immunohistochemistry of the 3rd branch of small arteries proximal to the intestine and to vascular responsiveness testing on day 3 through day 14. The innervation levels of calcitonin gene-related peptide-like immunoreactivity containing fibers and neuropeptide Y-like immunoreactivity containing fibers were markedly reduced on day 3 to day 14 and on day 5 to day 14 after the treatment, compared with those in sham-operated rats, respectively. In perfused mesenteric vascular beds isolated from phenol-treated rats, adrenergic nerve-mediated vasoconstriction and calcitonin gene-related peptide nerve-mediated vasodilation in response to periarterial nerve stimulation (2-12 Hz) were significantly decreased on day 3 and day 7. Neurogenic release of norepinephrine in phenol-treated rats on day 7 was significantly smaller that that in sham-operated rats. Nerve growth factor content in the mesenteric arteries of phenol-treated rats was significantly lower than that in sham-operated rats. Administration of nerve growth factor using osmotic mini-pumps for 7 days after the phenol treatment resulted in greater density of calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity fibers than in phenol-treated rats and restored decreased vascular responses to periarterial nerve stimulation. These results suggest that topical phenol-treatment of the mesenteric artery effectively induces functional denervation of perivascular nerves, which can be prevented or reversed by nerve growth factor treatment.

Effect of Adrenomedullin on Adrenergic Vasoconstriction in Mesenteric Resistance Arteries of the Rat

Adrenomedullin (AM) is a hypotensive peptide that belongs to a family of peptides structurally related to calcitonin gene-related peptide (CGRP). The present study examined the effect of AM on adrenergic nerve-mediated vasoconstriction in rat perfused mesenteric vascular beds without endothelium. Perfusion of AM at 0.1 nM but not 10 nM increased vasoconstrictor responses to periarterial nerve stimulation (PNS) (1-4 Hz), while AM at 10 nM significantly attenuated vasoconstriction induced by bolus injection of norepinephrine (NE). In preparations treated with capsaicin (a CGRP depletor), pressor responses to both PNS and NE injection were markedly attenuated by AM. Perfusion of CGRP(8-37) (a CGRP-receptor antagonist) significantly potentiated the PNS- but not the NE-induced vasoconstriction. Combined perfusion of CGRP(8-37) and AM had no effect on the PNS-induced response and antagonized the inhibitory effect of AM on the NE-induced response. AM(2-52) (an AM-receptor antagonist) did not influence the effect of AM. These findings suggest that AM facilitates adrenergic vasoconstriction by inhibiting neurotransmission of CGRP-containing nerves, which counteract adrenergic nerve-mediated vasoconstriction.

Characterization of cannabinoid modulation of sensory neurotransmission in the rat isolated mesenteric arterial bed

The present study investigated the effects of different classes of cannabinoid (CB) receptor ligands on sensory neurotransmission in the rat isolated mesenteric arterial bed. Electrical field stimulation of the mesenteric bed evoked frequency-dependent vasorelaxation due to the activation of capsaicin-sensitive sensory nerves and release of calcitonin gene-related peptide (CGRP). The CB(1)/CB(2) cannabinoid agonists WIN55,212 [(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone] and CP55,940 [(-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl) cyclohexanol] (0.01-1 microM) attenuated sensory neurogenic relaxation in a concentration-dependent manner. At 0.1 microM, WIN55,212 and CP55,940 were largely ineffective in the presence of the CB(1) antagonists SR141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichloro phenyl)-4-methyl-3-pyrazole-carboxamide] and LY320135 [[6-methoxy-2-(4-methoxyphenyl)benzo[b]-thien-3-yl][4-cyanophenyl] methanone] (1 microM), but their inhibitory actions remained in the presence of the CB(2)-selective antagonist SR144528 [N-[1S)-endo-1,3,3,-trimetyl bicyclo [2.2.1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide] (1 microM). The CB(1)/CB(2) agonist Delta(9)-tetrahydrocannabinol (THC) (1 microM) attenuated sensory neurogenic relaxations, as did the CB(2) agonist JWH-015 [(2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone]. The inhibitory actions of both THC and JWH-015 were still evident in the presence of SR141716A (1 microM) and SR144528 (1 microM). None of the cannabinoid agonists investigated had an effect on vasorelaxation elicited by exogenous CGRP, indicating a prejunctional mechanism. These data demonstrate that different classes of cannabinoid agonists attenuate sensory neurotransmission via a prejunctional site and provide evidence for mediation by a CB(1) and/or a non-CB(1)/CB(2) receptor.

Female Sex Steroid Hormones and Pregnancy Regulate Receptors for Calcitonin Gene-Related Peptide in Rat Mesenteric Arteries, but Not in Aorta1

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Different effects of acute clenbuterol on vasomotor response in mesenteric arteries from young and old spontaneously hypertensive rats

We analysed the influence of aging on the acute effect of clenbuterol, a beta(2)-adrenoceptor agonist, on the vasoconstrictor response induced by electrical field stimulation in mesenteric arteries from young and old spontaneously hypertensive rats (SHRs). Clenbuterol increased the contraction elicited by electrical field stimulation in arteries from both groups, and this was prevented by propranolol. N(G)-nitro-L-arginine methyl ester (L-NAME) also increased the electrical field stimulation-elicited contractions in arteries from both age groups. However, pretreatment with capsaicin increased the electrical field stimulation-induced contractions in young SHRs, but did not modify it in old SHRs. In segments from young SHRs, the treatment with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8-37), induced an increase in the electrical field stimulation-induced vasoconstrictor response that was not modified by the subsequent addition of capsaicin. Addition of clenbuterol to L-NAME-treated segments from both groups further increased the response to electrical field stimulation. In segments from young SHRs, clenbuterol failed to increase the electrical field stimulation-induced response in the capsaicin-treated segments, but the response was increased by the subsequent addition of L-NAME. The addition of L-NAME to the clenbuterol-treated segments from old SHRs did not modify the enhanced electrical field stimulation response. Electrical field stimulation induced a similar tritium release in arteries from young and old SHRs preincubated with [3H]noradrenaline. In arteries from young SHRs, isoproterenol increased this release and the increase was abolished by propranolol. Clenbuterol increased the stimulated tritium overflow and exogenous noradrenaline response only in segments from old SHRs, and both effects were abolished by propranolol. To summarize and conclude, clenbuterol increased the electrical field stimulation-induced contraction in segments from both age groups. In young SHRs, clenbuterol seems to inhibit CGRP release, while in old SHRs, it increases the release of and response to noradrenaline and decreases neuronal nitric oxide (NO) release.

Effects of pregnancy and female sex steroid hormones on calcitonin gene-related peptide content of mesenteric artery in rats

Calcitonin gene-related peptide (CGRP) levels in plasma and the dorsal root ganglia (DRG) are increased during pregnancy and in ovariectomized rats injected with ovarian hormones. Vasodilatory responses to CGRP are also increased in these animals. In the present study, we hypothesized that pregnancy and ovarian hormones elevate the contents of CGRP in perivascular nerves. We assessed CGRP-dependent mesenteric vascular relaxation induced by electrical field stimulation (EFS) and arterial content of CGRP. Because the mesenteric artery represents resistance vessels, segments of mesenteric arteries collected from female rats at different stages of the estrous cycle, pregnancy, or postpartum and from male rats were used in this study. The EFS-induced relaxation in the presence and absence of CGRP(8-37), an antagonist of CGRP, was used to measure CGRP-dependent relaxation, and radioimmunoassay (RIA) of tissue homogenates was used to assess changes in CGRP content in mesenteric branch arteries. The results show that CGRP-dependent, EFS-induced relaxation response was lower in female rats at diestrus and proestrus than in male rats, and no statistically significant differences were observed between Gestational Day 20 and Postpartum Day 2. The RIA revealed significantly lower mesenteric artery CGRP levels in female rats at proestrus, gestation, and postpartum than in female rats at diestrus or in male rats. We conclude that no correlation exists between CGRP-dependent, EFS-induced relaxation and CGRP content in the mesenteric arteries of these animal groups. Because both CGRP levels in DRG and serum are reported to be elevated, the reduced CGRP content in the vasculature during pregnancy and proestrus implicate enhanced basal release of CGRP at the nerve terminal in these animals.

Effects of the vasoactive neuropeptides calcitonin gene-related peptide, substance P and vasoactive intestinal polypeptide on skin temperature in ovariectomized rats

The effects of three vasoactive neuropeptides, calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal polypeptide (VIP), on vasodilation and skin temperature were investigated in ovariectomized (OVX) and sham-operated control rats. CGRP (0.01-1 nmol), VIP (0.01-10 nmol) and SP (0.1-100 nmol) produced vasodilation in PGF(2 alpha) (10 microM)-induced contraction of mesenteric vascular beds isolated from OVX and sham-operated rats in a dose-dependent manner. Intravenous injection of CGRP (1-10 microg/kg), VIP (10-50 microg/kg) and SP (10-50 microg/kg) elevated the skin temperature in OVX and sham-operated rats in a dose-dependent manner. CGRP had the greatest effect on both parameters, followed by VIP, with the smallest effect in SP. These parallel increases of vasodilation and skin temperature with CGRP were significantly greater in OVX rats than in sham-operated rats. However, no significant differences were observed in VIP- or SP-induced vasodilation and skin temperature increases between OVX and sham-operated rats. These results suggest not only that CGRP is closely related to the elevation of skin temperature but also that CGRP-induced responses are more affected by ovarian hormone deficiency.

Endothelial nitric oxide modulates perivascular sensory neurotransmission in the rat isolated mesenteric arterial bed

1. A possible role of nitric oxide (NO) as a modulator of capsaicin-sensitive sensory neurotransmission in blood vessels was investigated in the rat isolated mesenteric arterial bed. 2. Electrical field stimulation (EFS) of methoxamine-preconstricted mesenteric beds elicited frequency-dependent vasorelaxation mediated by capsaicin-sensitive sensory nerves. N(G)-nitro-L-arginine methyl ester (L-NAME, 10 and 300 microM) and 7-nitroindazole (7-NI, 100 microM), inhibitors of nitric oxide synthase (NOS), augmented sensory neurogenic vasorelaxation. D-NAME (300 microM), 6-aminoindazole (100 microM) and N(omega)-propyl-L-arginine (50 nM), a selective inhibitor of neuronal NOS, were without effect. The effect of 10 microM L-NAME was reversed by L-arginine (1 mM), the substrate for NOS. 3. L-NAME (300 microM) and 7-NI (100 microM) had no significant effect on vasorelaxations to calcitonin gene-related peptide (CGRP), the principal motor neurotransmitter of capsaicin-sensitive sensory nerves in rat mesenteric arteries, or to capsaicin, indicating a prejunctional action. The inhibitors of NOS had no effect on vasorelaxation to forskolin, but augmented vasorelaxation to sodium nitroprusside (SNP). 4. Removal of the endothelium augmented sensory neurogenic vasorelaxation, but did not affect vasorelaxation to CGRP, indicating a prejunctional action of endothelial NO. 5. In the absence of endothelium, L-NAME (300 microM) inhibited, and 7-NI (100 microM) caused no further augmentation of sensory neurotransmission. 6. SNP (100 nM), a nitric oxide donor, attenuated sensory neurogenic relaxations to EFS. 7. In rat isolated thoracic aortic rings, L-NAME (100 microM) and 7-NI (100 microM) attenuated concentration-dependent relaxations to acetylcholine. 8. These data show that NO modulates sensory neurotransmission evoked by EFS of the rat isolated mesenteric arterial bed, and that when NO synthesis is blocked sensory neurogenic relaxation is augmented. The source of NO is the vascular endothelium.

Cardiovascular effects of cannabinoids

The prototypic endocannabinoid, anandamide, and synthetic analogues have been shown to elicit pressor and depressor effects, bradycardia, vasorelaxation, and inhibition of neurotransmission in the central and peripheral nervous systems. Cannabinoid-mediated inhibition of neurotransmission is mediated by inhibition of voltage-gated Ca(2+) channels and adenylyl cyclase and activation of inwardly rectifying K(+) channels. The precise mechanisms underlying the vasorelaxant actions of cannabinoids are currently unclear, but might involve both receptor-dependent and -independent and endothelium-dependent and -independent pathways. Mechanisms proposed have included the release of endothelial autacoids, activation of myoendothelial gap junctions, activation of the Na(+) pump, activation of K(+) channels, inhibition of Ca(2+) channels, and activation of vanilloid receptors, leading to the release of sensory neurotransmitters. Pathophysiologically, the vasodilator actions of endocannabinoids have been implicated in the hypotension associated with both septic and haemorrhagic shock, but their physiological significance remains to be determined.

Regulation of vascular function by perivascular calcitonin gene-related peptide-containing nerves

The rat mesenteric artery is innervated by nonadrenergic noncholinergic (NANC) vasodilator nerves in which calcitonin gene-related peptide (CGRP), a potent vasodilator peptide, acts as a vasodilator transmitter. The inhibition of CGRPergic nerve function potentiates a vasoconstrictor response mediated by the sympathetic adrenergic nerve, suggesting that CGRPergic nerves inhibit adrenergic function and play a role in the regulation of mesenteric vascular tone. In contrast, norepinephrine released from adrenergic nerves presynaptically inhibits neurotransmission of CGRPergic nerves. Thus, both nerves reciprocally control the vascular tone. Pathophysiological studies have shown that an age-related decrease in CGRPergic nerve-mediated vasodilation, neurogenic CGRP release and CGRP mRNA levels in the dorsal root ganglia are found in spontaneously hypertensive rats (SHR), indicating a reduced function of CGRPergic nerves. Long-term treatment with angiotensin converting enzyme inhibitor and angiotensin II-receptor antagonist restores the reduced function of CGRPergic nerves, suggesting the involvement of angiotensin II in the malfunction of CGRPergic nerves in SHR.

Adrenomedullin inhibits neurotransmission of calcitonin gene-related peptide (CGRP)-containing vasodilator nerves in rat mesenteric resistance arteries

We have reported that the rat mesenteric resistance artery has innervation of calcitonin gene-related peptide (CGRP)-containing vasodilator nerves (CGRPergic nerves). We also demonstrated that adrenomedullin (AM) causes mesenteric vasodilation through activation of CGRP receptors. The present study was designed to examine the effect of AM on neurotransmission of CGRPergic nerves in rat mesenteric arteries. In preconstricted preparations without endothelium, periarterial nerve stimulation (PNS, 1 and 2 Hz) induced a frequency-dependent vasodilation. A bolus injection of CGRP (10 pmol) into the perfusate also caused a vasodilation. AM (0.1 to 10 nM) concentration-dependently caused 40% to 60% inhibition of the PNS-induced vasodilation, but AM did not attenuate vasodilation induced by exogenous CGRP injection. The inhibitory effect of AM (10 nM) on PNS-induced vasodilation was further potentiated by CGRP [8-37] (CGRP receptor antagonist, 50 nM), which attenuated the vasodilator response to the CGRP injection. Combined perfusion of AM [22-52] (AM receptor antagonist, 10 to 100 nM) resulted in further inhibition of PNS-induced neurogenic vasodilation without affecting the vasodilator response to the CGRP injection. CGRP [8-37] but not AM [22-52] antagonized vasodilation induced by AM perfusion. These findings suggest that AM presynaptically inhibits neurotransmission of CGRPergic nerves, probably decreasing CGRP release, via receptors different from CGRP receptors.

Adrenergic nerves mediate acetylcholine-induced endothelium-independent vasodilation in the rat mesenteric resistance artery

Mechanisms underlying acetylcholine-induced endothelium-independent vasodilation were studied in the rat mesenteric vascular bed isolated from Wistar rats. In preparations without endothelium, and contracted by perfusion with Krebs solution containing methoxamine (2-7 microM), perfusion of acetylcholine (1-100 microM) for 1 min produced a concentration-dependent vasodilation. Denervation of denuded preparations by cold storage (4 degrees C for 72 h) abolished the acetylcholine-induced vasodilation; 10 and 100 nM atropine abolished 1 and 10 microM acetylcholine-induced vasodilation, but it inhibited only 20% of vasodilation by 100 microM acetylcholine. The acetylcholine-induced atropine-resistant vasodilation was inhibited by 10 and 100 microM hexamethonium, 5 microM guanethidine, 50 microM bretylium, in vitro 6-hydroxydopamine (2 mM for 20 min, twice), 1 microM capsaicin and 0.5 microM calcitonin gene-related peptide (CGRP)-(8-37) (CGRP receptor antagonist). These findings suggest that the acetylcholine-induced endothelium-independent nicotinic vasodilation requires the presence of intact adrenergic nerves, and is mediated by endogenous CGRP released from CGRP-containing nerves.

Cannabinoid inhibition of capsaicin-sensitive sensory neurotransmission in the rat mesenteric arterial bed

The present study investigated whether cannabinoids can modulate neurotransmission mediated by capsaicin-sensitive sensory nerves in the rat isolated mesenteric arterial bed. Sensory neurogenic vasorelaxation mediated by electrical field stimulation was concentration-dependently attenuated by HU210 (0.1-3 microM), a cannabinoid receptor agonist (from 62+/-8.3% to 6+/-2.1% at 3 microM HU210). HU210 had no effect on relaxation to exogenous calcitonin gene-related peptide, indicating a prejunctional action. The action of HU210 (1 microM) was not affected by LY320135 (1 microM) or SR144528 (1 microM), cannabinoid CB(1) and CB(2) receptor antagonists, respectively. SR141716A (0.01-1 microM), a cannabinoid CB(1) receptor antagonist, concentration-dependently augmented vasorelaxation to electrical field stimulation, but had no effect on responses to calcitonin gene-related peptide and capsaicin, indicating a possible role of endogenous cannabinoids in sensory neurotransmission in rat mesenteric arteries. These data show that the cannabinoid receptor agonist HU210 inhibits prejunctionally sensory neurotransmission in rat mesenteric arteries and that this action is independent of cannabinoid CB(1)- or CB(2)-like receptors.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Heterogeneity in mechanisms underlying vasodilatory responses in small arteries of the rat hepatic mesentery

We have characterised nerve-mediated vasodilations in small arteries of the rat hepatic mesentery. Stimulation of sympathetic nerves (10 Hz, 10 s) produced a vasodilation which was abolished by the beta-adrenoceptor antagonist, propranolol (2 x 10(-6) M), but was unaffected by NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M). Stimulation of sensory nerves produced a large vasodilation that was abolished by capsaicin (10(-6) M). This vasodilation was unaffected by L-NAME (10(-5) M), but significantly reduced by the calcitonin gene related peptide (CGRP) antagonist, CGRP8-37 (10(-6) M), or inhibition of adenylate cyclase (SQ22356, 2 x 10(-5) M; 2',5'-dideoxyadenosine, 2 x 10(-4) M). Stimulation of cholinergic nerves produced a small vasodilation which was significantly reduced by scopolamine (10(-6) M). Expression of mRNA for CGRP1 receptors, muscarinic m2, m3 and m5 receptors and neurokinin1 (NK1) and NK3, receptors was detected. Perivascular nerves were immunoreactive for CGRP and substance P. No role was found for substance P, neuronal NO, ATP or adenosine in nerve-mediated responses. L-NAME (10(-5) M) potentiated vasoconstrictions following sympathetic nerve stimulation. This effect was reversed by L-arginine (10(-3) M) and cromakalim (10(-6) M) and mimicked by glybenclamide (10(-5) M), thus implicating KATP channels. Vasodilation in response to sensory nerve stimulation was directly proportional to the level of preconstriction, while vasodilation in response to neurogenic or applied acetylcholine was inhibited at high levels of preconstriction. We hypothesize that, under conditions of intensive vasoconstriction, some endothelial-dependent vasodilations may be less important than vasodilations activated directly through the smooth muscle.

Bioactive beta-bend structures for the antagonist halpha CGRP(8 - 37) at the CGRP(1) receptor of the rat pulmonary artery

The aim of this study was to determine beta-bend structures and the role of the N- and C-terminus in the antagonist halpha CGRP(8 - 37) at the rat pulmonary artery CGRP receptor mediating halpha CGRP relaxation. Halpha CGRP(8 - 37) Pro(16) (10(-6) M), with a bend-biasing residue (proline) at position 16, did not antagonize halpha CGRP responses, while a structure-conserving amino acid (alanine(16)) at the same position retained antagonist activity (apparent pK(B) 6.6+/-0.1; 10(-6) M). Halpha CGRP(8 - 37) Pro(19) (10(-6) M), with proline at position 19 was an antagonist (apparent pK(B) 6.9+/-0.1). Incorporation of a beta-bend forcing residue, BTD (beta-turn dipeptide), at positions 19 and 20 in halpha CGRP(8 - 37) (10(-6) M) antagonized halpha CGRP responses (apparent pK(B) 7.2+/-0.2); and BTD at positions 19,20 and 33,34 within halpha CGRP(8 - 37) was a competitive antagonist (pA(2) 7.2; Schild plot slope 1.0+/-0.1). Halpha CGRP(8 - 37) analogues, substituted at the N-terminus by either glycine(8) or des-NH(2) valine(8) or proline(8) were all antagonists (apparent pK(B) 6.9+/-0.1; (10(-6) M), 7.0+/-0.1 (10(-6) M), and pA(2) 7.0 (slope 1.0+/-0.2), respectively); while replacements by proline(8) together with glutamic acid(10,14) in halpha CGRP(8 - 37) (10(-6) M) or alanine amide(37) at the C-terminus of halpha CGRP(8 - 37) (10(-5) M) were both inactive compounds. In conclusion, possible bioactive structures of halpha CGRP(8 - 37) include two beta-bends (at 18 - 21 and 32 - 35), which were mimicked by BTD incorporation. Within halpha CGRP(8 - 37), the N-terminus is not essential for antagonism while the C-terminus may interact directly with CGRP(1) receptors in the rat pulmonary artery.

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.

Vanilloid receptors on sensory nerves mediate the vasodilator action of anandamide

The endogenous cannabinoid receptor agonist anandamide is a powerful vasodilator of isolated vascular preparations, but its mechanism of action is unclear. Here we show that the vasodilator response to anandamide in isolated arteries is capsaicin-sensitive and accompanied by release of calcitonin-gene-related peptide (CGRP). The selective CGRP-receptor antagonist 8-37 CGRP, but not the cannabinoid CB1 receptor blocker SR141716A, inhibited the vasodilator effect of anandamide. Other endogenous (2-arachidonylglycerol, palmitylethanolamide) and synthetic (HU 210, WIN 55,212-2, CP 55,940) CB1 and CB2 receptor agonists could not mimic the action of anandamide. The selective 'vanilloid receptor' antagonist capsazepine inhibited anandamide-induced vasodilation and release of CGRP. In patch-clamp experiments on cells expressing the cloned vanilloid receptor (VR1), anandamide induced a capsazepine-sensitive current in whole cells and isolated membrane patches. Our results indicate that anandamide induces vasodilation by activating vanilloid receptors on perivascular sensory nerves and causing release of CGRP. The vanilloid receptor may thus be another molecular target for endogenous anandamide, besides cannabinoid receptors, in the nervous and cardiovascular systems.

Endogenous calcitonin gene-related peptide suppresses vasoconstriction mediated by adrenergic nerves in rat mesenteric resistance blood vessels

The role of perivascular calcitonin gene-related peptide (CGRP)-containing nerves in the modulation of adrenergic nerve-mediated vasoconstrictions was studied in the rat perfused mesenteric vascular bed. A frequency-dependent vasoconstriction induced by periarterial nerve stimulation (1-6 Hz) of the bed was significantly potentiated by perfusion of 1 microM CGRP-(8-37) (CGRP receptor antagonist) or to a similar extent after treatment with 500 nM capsaicin. In the preparations treated with capsaicin, CGRP-(8-37) caused a small potentiation of periarterial nerve stimulation-induced vasoconstriction. Exogenous CGRP (0.1-1 nM) concentration-dependently attenuated the augmented vasoconstriction in response to periarterial nerve stimulation after treatment with capsaicin. However, exogenous CGRP (1 nM) did not attenuate the periarterial nerve stimulation-induced vasoconstriction in the bed untreated with capsaicin. These results suggest that endogenous CGRP, which is released from CGRP-containing nerves, suppresses the adrenergic nerve function involved in mechanisms regulating the tone of resistant blood vessels.

Nonadrenergic noncholinergic vasodilation of guinea pig pulmonary arteries is mediated by nitric oxide

Nonadrenergic noncholinergic (NANC) mediated vasodilation may contribute to the maintenance of low pulmonary vascular tone. The NANC neurotransmitters, nitric oxide (NO) and the sensory neuropeptides, substance P and calcitonin gene related peptide (CGRP), were investigated as possible mediators of NANC vasodilation in guinea pig pulmonary arteries. Fresh guinea pig pulmonary artery rings, with and without an intact endothelium, were mounted in organ baths containing Krebs solution and precontracted with the prostaglandin F2α analogue U44069. In both endothelium-intact and denuded vessels, electrical field stimulation (1-12 Hz) in the presence of guanethidine and atropine resulted in a frequency-dependent vasodilation. The peptide fragment hCGRP8-37, a competitive antagonist of the CGRP receptors, the peptide fragment NK1 antagonist SP4-11, and the nonpeptide NK1 antagonist RP67580 had no effect on NANC vasodilation. In both endothelium-intact and denuded vessels, NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis, inhibited NANC vasodilation, an effect that was reversible with L-arginine. We conclude that NANC vasodilation in guinea pig pulmonary arteries is mediated predominantly through NO activity.Key words: nonadrenergic noncholinergic, pulmonary artery, nitric oxide, vasodilation.

Effect of omega-conotoxin GVIA and omega-agatoxin IVA on the capsaicin-sensitive calcitonin gene-related peptide release and autoregulatory vasodilation in rat pial arteries

This study assesses the effect of neuronal voltage-sensitive Ca2+ channel blockers, omega-conotoxin GVIA (CTX), and omega-agatoxin IVA (AgTX) on the vasodilation and release of calcitonin gene-related peptide (CGRP), both of which were induced by either application of capsaicin or acute stepwise hypotension. Changes in pial arterial diameter were determined directly through a closed cranial window. The vasodilation of pial artery induced by either CGRP (0.1 micromol/L) or capsaicin (0.3 micromol/L) was significantly inhibited by CGRP(8-37) (0.1 micromol/L) (P < 0.05 and P < 0.05, respectively). The autoregulatory vasodilation to acute stepwise hypotension was severely attenuated by pretreatment with either CTX or AgTX. When the hypotension was kept for 2, 4, and 10 minutes, the releasable CGRP-like immunoreactivity (CGRP-LI) level (vehicle, 13.4+/-1.5 fmol/mm2/30 min) by 10 micromol/L capsaicin from the isolated pial arteries was significantly reduced in the 4- and 10-minute hypotension groups (11.3+/-1.2 fmol/mm2/30 min, P < 0.05, and 11.1+/-1.5 fmol/mm2/30 min, P < 0.05, respectively), but not in 2-min group. Moreover, the CGRP-LI level released by 10 micromol/L capsaicin (13.7+/-0.9 fmol/mm2/30 min) also was significantly depressed by pretreatment with 1 micromol/L CTX to 10.4+/-1.0 fmol/mm2/30 min (P < 0.01) and with 0.1 micromol/L AgTX to 8.7(1.7 fmol/mm2/30 min (P < 0.001), as well as by pretreatment with 10 micro-mol/L capsaicin (6.0+/-1.6 fmol/ mm2/30 min, P < 0.001). These results suggest that the neuronal N- and P-type voltage-sensitive Ca2+ channels are implicated in the release of CGRP from capsaicin-sensitive perivascular sensory nerves in response to acute hypotension, and that the released CGRP may contribute to the autoregulatory vasodilation in the cerebral microcirculation.

Uterine relaxation responses to calcitonin gene-related peptide and calcitonin gene-related peptide receptors decreased during labor in rats

OBJECTIVES

Our purpose was to investigate (1) whether uterine relaxation responses to calcitonin gene-related peptide are differentially regulated during pregnancy and labor, (2) the involvement of nitric oxide in smooth muscle relaxant action of calcitonin gene-related peptide in the rat uterus, (3) whether receptors for calcitonin gene-related peptide are expressed in rat uterus, and if so (4) whether the concentrations of these receptors are differently regulated during pregnancy and labor.

STUDY DESIGN

Rats were killed on day 18 of gestation, at the time of spontaneous labor, or postpartum day 2. The uteri were removed for in vitro contractility measurements, nitric oxide production, and calcitonin gene-related peptide receptor binding assay.

RESULTS

(1) Calcitonin gene-related peptide induced a dose-dependent relaxation in spontaneously contracting uterine strips from pregnant rats on day 18 of gestation; (2) the relaxation effects of calcitonin gene-related peptide on the uterus were decreased during spontaneous delivery at term and post partum compared with that during pregnancy; (3) calcitonin gene-related peptide-induced relaxation was inhibited by pretreatment of the uterine tissue with a calcitonin gene-related peptide receptor antagonist, calcitonin gene-related peptide(8-37); (4) nitric oxide synthesis inhibitor (N(G)-nitro-L-arginine methyl ester) and soluble guanylate cyclase inhibitor (LY83583) significantly decreased calcitonin gene-related peptide-induced relaxation of the rat uterus during pregnancy; (5) calcitonin gene-related peptide increased the uterine nitric oxide production in pregnant rats, and this increase was obliterated in the presence of calcitonin gene-related peptide(8-37); and (6) calcitonin gene-related peptide receptors are present in rat uterus, and the concentration of these receptors dramatically increases during pregnancy and decreases during labor at term.

CONCLUSIONS

Calcitonin gene-related peptide inhibits uterine spontaneous contractions in rats during pregnancy but not during labor and post partum. The inhibitory effects of calcitonin gene-related peptide on uterine contractility appear to be modulated, at least in part, by the activation of nitric oxide generation in the rat uterus. Changes in calcitonin gene-related peptide receptors could contribute to the changes in calcitonin gene-related peptide-mediated uterine relaxation during pregnancy and labor.

Effects of calcitonin and calcitonin gene-related peptide on the substance P-mediated secretion of fluid from the rat submandibular gland

1. The effects of rat calcitonin gene-related peptide (rCGRP), rat calcitonin (rCT) and salmon calcitonin (sCT) on the substance P-mediated (SP-mediated) secretion of fluid from the rat submandibular gland were investigated. 2. Rat CGRP potentiated and prolonged the SP-mediated secretion of fluid from the rat submandibular gland in a dose-dependent manner. CGRP also enhanced methacholine- and phenylephrine-mediated secretion of fluid. 3. The potentiating effect of the combination of rCGRP and SP was somewhat reduced by pretreatment with spantide, human CGRP8-37 and atropine but not by pretreatment with phentolamine or with propranolol. 4. Salmon CT at a low dose mimicked the effect of rCGRP on the SP-mediated secretion of fluid, but its potency was lower than that of rCGRP. However, rCT had no effect on the SP-mediated secretion of fluid. 5. These results suggest that the potentiating effects of rCGRP and SP might involve cholinergic receptors, as well as CGRP and tachykinin receptors, and that sCT, but not rCT, is able to mimic rCGRP in potentiating the secretion of fluid induced by SP.

Involvement of calcitonin gene-related peptide (CGRP) receptors in insulin-induced vasodilatation in mesenteric resistance blood vessels of rats

1. The vascular effect of insulin in the mesenteric resistance blood vessel and the role of calcitonin generelated peptide (CGRP)-receptor in insulin-induced vascular responsiveness were investigated in rats. 2. The mesenteric vascular beds isolated from Wistar rats were perfused with Krebs solution, and perfusion pressure was measured with a pressure transducer. In preparations contracted by perfusion with Krebs solution containing methoxamine in the presence of guanethidine, the perfusion of insulin (from 0.1 to 3000 nM) caused a concentration-dependent decrease in perfusion pressure due to vasodilatation. The pD2 value and maximum relaxation (%) were 6.94+/-0.22 and 43.9+/-5.2, respectively. 3. This vasodilator response to insulin was unaffected by 100 nM propranolol (beta-adrenoceptor antagonist) plus 100 nM atropine (muscarinic cholinoceptor antagonist), 100 microM L-NG-nitroarginine (nitric oxide synthase inhibitor), 1 microM ouabain (Na+-K+ ATPase inhibitor), or 1 microM glibenclamide (ATP sensitive K+-channel inhibitor). 4. In preparations without endothelium, perfusion of insulin produced a marked vasodilatation. The pD2 value and maximum relaxation (%) were 7.62+/-0.21 and 81.0+/-4.6, respectively, significantly greater than in preparations with intact endothelium. 5. The vasodilator responses to insulin in the preparations without endothelium were significantly inhibited by CGRP[8 37], a CGRP receptor antagonist, whereas pretreatment with capsaisin, a toxin for CGRP-containing nerves, did not affect insulin-induced vasodilatation. 6. These results suggest that insulin induces non-adrenergic, non-cholinergic and endothelium-independent vasodilatation, which is partially mediated by CGRP receptors.

Nitric oxide is a sensory nerve neurotransmitter in the mesenteric artery of guinea pig

Previous studies have shown that the guinea pig inferior mesenteric artery receives spinal sensory vasodilatory innervation, which can be activated by colon distention and electrical nerve stimulation. In the present study, we investigated the hypotheses that nitric oxide synthase (NOS) is present in guinea pig primary sensory neurons in the dorsal root ganglion (DRG) and in nerve fibers surrounding the mesenteric arteries, and that nitric oxide (NO) is a sensory neurotransmitter in the inferior mesenteric artery in vitro. Double-labeling immunohistochemistry showed that neuronal NOS-IR was found in 12% of cells of guinea pig thoracic and lumbar DRGs; in 95.1% of these cells it was colocalized with substance P (SP), and SP immunoreactivity (SP-IR) was present in 23% of cells of the same DRGs. Neuronal NOS-like immunoreactivity was localized in nerve fibers surrounding guinea pig mesenteric artery and 25% of them were double stained with SP-IR. Endothelium-denuded inferior mesenteric artery preparations in vitro were incubated with guanethidine (30 microns, 30 min) and pre-contracted with methoxamine (30 microns). The NO donors, sodium nitroprusside (1 micron) and L-nitrosocysteine (300 microns), produced 91.0 +/- 5.5 and 90.4 +/- 9.6% vasodilatation of total vasodilatation in the vessel segments, respectively, which was capsaicin- or tetrodotoxin-insensitive. Repetitive electrical field stimulation of the preparations produced a frequency-dependent vasodilatation which was reduced by pretreatment with capsaicin or by tetrodotoxin (10 microns). The NOS inhibitor N omega-nitro-L-arginine (L-NNA) (100 microns, 30 min) diminished the nerve-evoked vasodilatation from 41.8 +/- 8.4 to 21.4 +/- 9.7% at 2 Hz and from 50.8 +/- 5.6 to 19.0 +/- 7.3% at 15 Hz (P < 0.05), whereas NG-nitro-L-arginine methyl ester (L-NAME, 100 microns-1 mM) did not significantly inhibit the relaxation. The stereo isomer nitro-D-arginine (D-NNA, 100 microns, 30 min) was ineffective. These findings suggest that NO is a neurotransmitter released from primary sensory nerves which mediates vasodilation in vitro.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Spatial heterogeneity of the effects of calcitonin gene-related peptide (CGRP) on the microvasculature of ligaments in the rabbit knee joint

1. Experiments were performed in anaesthetized rabbits to examine the effects of calcitonin gene-related peptide (CGRP) and the CGRP antagonist CGRP8-37 on blood flow to the medial collateral ligament of the knee joint. 2. Topical application of CGRP (10(-13) to 10(-9) mol) to the exposed external surface of eight knee joints resulted in dose-dependent dilatation of vessels in both the ligament and the joint capsule. The magnitude of this response varied significantly in different regions of the medial collateral ligament, with the 10(-9) mol dose of CGRP giving the maximum response (101.5 +/- 25.3% increase) at the femoral insertion site of the medial collateral ligament and lowest (23.1 +/- 8.8%) at the tibial insertion site. 3. Topical application of CGRP8-37 (0.1, 1 and 10 nmol) produced dose-dependent constriction of vessels in the ligament and the joint capsule in five knees, with a trend towards the greatest effect occurring at the femoral insertion site (45.8 +/- 8.1% reduction in blood flow). With the 10 nmol dose, the vasoconstrictor response at the femoral insertion site differed significantly (P<0.05) from the responses obtained at the tibial insertion and joint capsule sites. 4. Topical application of CGRP8-37 (0.1, 1 and 10 nmol) to four chronically denervated knees produced substantially smaller vasoconstrictor responses at all sites. At the femoral insertion site, where 10 nmol CGRP8-37 normally produces a 45.8 +/- 8.1% reduction in blood flow (n=8), ten days following denervation this response was reduced to 6.5 +/- 6.1%, this difference being significant (P=0.01). 5. Adrenaline was applied topically to augment blood vessel tone, in order to establish how effectively co-administration of CGRP would offset this increase in tone. Adrenaline (10(-10) mol) produced vasoconstriction at all sites (n=6). In the capsule this vasoconstriction was virtually abolished when CGRP (10(-9) mol) was co-administered with adrenaline but in the ligament vasodilatation occurred at all sites. This vasodilatation was significantly greater at the femoral insertion site compared to the tibial insertion and mid ligament sites (P<0.05 for both) and the capsule (P<0.01). 6. Topical application of substance P (10(-10) or 10(-9) mol) failed to elicit dilatation of ligament blood vessels. 7. These results suggest that endogenous CGRP may play an important role in regulating blood flow to different structures in and around the knee joint.

Modulation of synovial blood flow by the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37)

1. The effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37) on blood flow in the knee joint of the anaesthetized rat was investigated. 2. Synovial blood flow in both exposed and intact, skin-covered knees was measured by laser Doppler perfusion imaging. 3. Topical application of CGRP(8-37) caused a dose-dependent fall in synovial blood flow in the exposed knee joint of the rat. At low (1.5 nmol) doses of CGRP(8-37) there was no significant effect on synovial blood flow. In rats treated with 7.5 nmol CGRP(8-37) there was a fall in synovial blood flow (maximum effect at 10 min: -28.8 +/- 4.6%; n=7), which returned to resting levels within 30 min. The highest dose (15 nmol) of antagonist used in this study caused a marked (maximum at 10 min: -35.6 +/- 9.3%; n=8), and prolonged (up to 30 min) fall in blood flow. 4. Ten days after surgical denervation, CGRP(9-37) (15 nmol, topical) had no significant effect on blood flow in the rat exposed knee joint (change in flux at 10 min: -5.1+/-3.6%; n=4). This suggests that CGRP(8-37) acts selectively to antagonize the actions of a neurally derived product, probably CGRP, on the rat synovial vasculature. 5. In skin-covered knee joints, intra-articular injection of CGRP(8-37) (15 nmol; bolus) elicited a significant fall in synovial blood flow (maximum effect at 10 min: -15.5 +/- 5.8%; n=6). 6. CGRP (0.01, 0.1 or 1.0 nmol; topical) caused a dose-dependent increase in exposed knee joint blood flow, which was attenuated by co-administration of 1.5 nmol CGRP(8-37). For example, 1 nmol CGRP elicited a peak increase in flux at 10 min of 94.7 +/- 31.8% (n=8) and 28.8 +/- 8.9% (n=7) in the absence and presence of CGRP(8-37), respectively. The vasodilator responses induced by acetylcholine (ACh) (10 nmol, topical; n=4-5) or sodium nitroprusside (SNP) (10 nmol, topical; n=4-5) were unaltered in the presence of CGRP(8-37) (1.5 nmol, topical). 7. Thus, the CGRP receptor antagonist CGRP(8-37) elicits vasoconstriction in the rat synovium. This suggests that the endogenous, basal release of CGRP may play a physiological role in the regulation of blood flow in the rat knee joint.