Calcitonin gene-related peptide (CGRP) and capsaicin-induced stimulation of heart contractile rate and force

Myocardial perfusion recovery induced by an α-calcitonin gene-related peptide analogue

BACKGROUND

Endogenous calcitonin gene-related peptide (CGRP) induces cardioprotective effects through coronary vasodilation. However, the systemic administration of CGRP induces peripheral vasodilation and positive chronotropic and inotropic effects. This study aims to examine the net effect on coronary perfusion of the systemically administered α-calcitonin gene-related peptide analogue, SAX, in rats during myocardial infarction.

METHODS

Forty Sprague-Dawley rats underwent myocardial infarction. Following left anterior descending artery occlusion, [99mTc]Tc-sestamibi was administered to determine the myocardial perfusion before treatment. Twenty minutes, 24 and 48 h after [99mTc]Tc-sestamibi injection, the rats were treated with either SAX or placebo. Final infarct size was determined three weeks later by [99mTc]Tc-sestamibi SPECT/CT scan.

RESULTS

Thirty-one rats survived the surgery and 20 completed the follow-up SPECT/CT scan (SAX n = 12; Placebo n = 8). At baseline, there was no difference in size of perfusion defect between the groups (P = .88), but at follow-up the SAX group had improved myocardial recovery compared to the placebo group (P = .04), corresponding to a relative perfusion recovery of 55% in SAX-treated rats.

CONCLUSION

The CGRP analogue, SAX, has a cardioprotective effect in this rat model of myocardial infarction, improving myocardial perfusion recovery after chronic occlusion of the coronary artery.

Capsaicin Inhibits Multiple Voltage-Gated Ion Channels in Rabbit Ventricular Cardiomyocytes in TRPV1-Independent Manner

Capsaicin is a naturally occurring alkaloid derived from chili pepper which is responsible for its hot, pungent taste. It exerts multiple pharmacological actions, including pain-relieving, anti-cancer, anti-inflammatory, anti-obesity, and antioxidant effects. Previous studies have shown that capsaicin significantly affects the contractility and automaticity of the heart and alters cardiovascular functions. In this study, the effects of capsaicin were investigated on voltage-gated ion currents in rabbit ventricular myocytes. Capsaicin inhibited rapidly activated (I_Kr) and slowly activated (I_Ks) K⁺ currents and transient outward (I_to) K⁺ current with IC₅₀ values of 3.4 µM,14.7 µM, and 9.6 µM, respectively. In addition, capsaicin, at higher concentrations, suppressed voltage-gated Na⁺ and Ca²⁺ currents and inward rectifier I_K1 current with IC₅₀ values of 42.7 µM, 34.9 µM, and 38.8 µM, respectively. Capsaicin inhibitions of I_Na, I_L-Ca, I_Kr, I_Ks, I_to, and I_K1 were not reversed in the presence of capsazepine (3 µM), a TRPV1 antagonist. The inhibitory effects of capsaicin on these currents developed gradually, reaching steady-state levels within 3 to 6 min, and the recoveries were usually incomplete during washout. In concentration-inhibition curves, apparent Hill coefficients higher than unity suggested multiple interaction sites of capsaicin on these channels. Collectively, these findings indicate that capsaicin affects cardiac electrophysiology by acting on a diverse range of ion channels and suggest that caution should be exercised when capsaicin is administered to carriers of cardiac channelopathies or to individuals with arrhythmia-prone conditions, such as ischemic heart diseases.

Alpha-Calcitonin Gene Related Peptide: New Therapeutic Strategies for the Treatment and Prevention of Cardiovascular Disease and Migraine

Alpha-calcitonin gene-related peptide (α-CGRP) is a vasodilator neuropeptide of the calcitonin gene family. Pharmacological and gene knock-out studies have established a significant role of α-CGRP in normal and pathophysiological states, particularly in cardiovascular disease and migraines. α-CGRP knock-out mice with transverse aortic constriction (TAC)-induced pressure-overload heart failure have higher mortality rates and exhibit higher levels of cardiac fibrosis, inflammation, oxidative stress, and cell death compared to the wild-type TAC-mice. However, administration of α-CGRP, either in its native- or modified-form, improves cardiac function at the pathophysiological level, and significantly protects the heart from the adverse effects of heart failure and hypertension. Similar cardioprotective effects of the peptide were demonstrated in pressure-overload heart failure mice when α-CGRP was delivered using an alginate microcapsules-based drug delivery system. In contrast to cardiovascular disease, an elevated level of α-CGRP causes migraine-related headaches, thus the use of α-CGRP antagonists that block the interaction of the peptide to its receptor are beneficial in reducing chronic and episodic migraine headaches. Currently, several α-CGRP antagonists are being used as migraine treatments or in clinical trials for migraine pain management. Overall, agonists and antagonists of α-CGRP are clinically relevant to treat and prevent cardiovascular disease and migraine pain, respectively. This review focuses on the pharmacological and therapeutic significance of α-CGRP-agonists and -antagonists in various diseases, particularly in cardiac diseases and migraine pain.

Acute Increase in Blood αCGRP at Maximal Exercise and Its Association to Cardiorespiratory Fitness, Carbohydrate Oxidation and Work Performed: An Exploratory Study in Young Men

Simple Summary

αCGRP is a neuropeptide that increases in blood during high-intensity exercise in humans. However, the physiological meaning of this molecular response is unknown. Previous experimental works in rodents have related this neuropeptide to several biological processes in the skeletal muscle tissue and cardiorespiratory physiology. Based on the data from these animal studies we hypothesized that in humans αCGRP release during exercise could be similarly associated to metabolic and cardiorespiratory responses. To test this hypothesis, we subjected a sample of physically active young men to an exercise test up to exhaustion while their oxygen uptake (VO_2max), CO₂ production (VCO₂), carbohydrate oxidation and performed work were measured. Blood samples were taken before the exercise test, at maximal intensity and after the volunteers have recovered, and the blood concentration of αCGRP was measured. We found that 2/3 of the volunteers responded to maximal exercise with an increase of their blood αCGRP concentration (responders), while the resting 1/3 did not (non-responders). We also found that VO_2max, VCO₂, carbohydrate oxidation and performed work were higher in the responders when compared to the non-responders. Therefore, our observations support that αCGRP release during exercise may be associated to physiological responses related to physical performance.

Abstract

This study aimed to explore if the acute variations in plasma concentration of α-calcitonin gene-related peptide (αCGRP) induced by a single maximal exercise bout may be associated to cardiorespiratory fitness and carbohydrate oxidation in humans. Twelve young adult Caucasian men (24.3 ± 0.9 years-old; 179.2 ± 1.9 cm of height; 23.9 ± 0.6 kg·m⁻² body mass index) performed a graded exercise test. A venous catheter was placed before testing, and blood samples were taken at baseline, maximal effort and recovery. αCGRP was measured in plasma using a commercial double-sandwich enzyme-linked-immunoassay. A two-way repeated measurements ANOVA was used to compare the values obtained at baseline, maximal effort and recovery. In the whole sample, αCGRP increased at maximal effort and its concentration correlated directly, albeit non-significantly, with the muscle mass normalised VO₂, VCO₂, carbohydrate oxidation and relative power. Two thirds of the participants showed an increase in αCGRP concentration at maximal effort. Post hoc analysis showed that in these individuals, the muscle mass normalised VO₂, VCO₂, carbohydrate oxidation rate and relative power were higher than in the participants lacking this molecular response. Therefore, our data suggest that (a) a majority of young men respond to exercise with an increase in blood αCGRP concentration; and (b) individuals exhibiting this response also show a higher cardiorespiratory fitness, carbohydrate oxidation and work performed. These findings suggest that this neuropeptide could act as an exerkine with potential effects on physical performance.

Knockout of α-calcitonin gene-related peptide attenuates cholestatic liver injury by differentially regulating cellular senescence of hepatic stellate cells and cholangiocytes

α-Calcitonin gene-related peptide (α-CGRP) is a 37-amino acid neuropeptide involved in several pathophysiological processes. α-CGRP is involved in the regulation of cholangiocyte proliferation during cholestasis. In this study, we aimed to evaluate if α-CGRP regulates bile duct ligation (BDL)-induced liver fibrosis by using a α-CGRP knockout (α-CGRP^-/-) mouse model. α-CGRP^-/- and wild-type (WT) mice were subjected to sham surgery or BDL for 7 days. Then, liver fibrosis and cellular senescence as well as the expression of kinase such as p38 and C-Jun N-terminal protein kinase (JNK) in mitogen-activated protein kinases (MAPK) signaling pathway were evaluated in total liver, together with measurement of cellular senescence in cholangiocytes or hepatic stellate cells (HSCs). There was enhanced hepatic expression of Calca (coding α-CGRP) and the CGRP receptor components (CRLR, RAMP-1 and RCP) in BDL and in both WT α-CGRP^-/- and BDL α-CGRP^-/- mice, respectively. Moreover, there was increased CGRP serum levels and hepatic mRNA expression of CALCA and CGRP receptor components in late-stage PSC samples compared to healthy control samples. Depletion of α-CGRP reduced liver injury and fibrosis in BDL mice that was associated with enhanced cellular senescence of hepatic stellate cells and reduced senescence of cholangiocytes as well as decreased activation of p38 and JNK MAPK signaling pathway. Cholangiocyte supernatant from BDL α-CGRP^-/- mice inhibited the activation and increased cellular senescence of cultured human HSCs (HHSCs) compared to HHSCs stimulated with BDL cholangiocyte supernatant. Taken together, endogenous α-CGRP promoted BDL-induced cholestatic liver fibrosis through differential changes in senescence of HSCs and cholangiocytes and activation of p38 and JNK signaling. Modulation of α-CGRP/CGRP receptor signaling may be key for the management of biliary senescence and liver fibrosis in cholangiopathies.

Sensory Neuropathy Affects Cardiac miRNA Expression Network Targeting IGF-1, SLC2a-12, EIF-4e, and ULK-2 mRNAs

Background: Here we examined myocardial microRNA (miRNA) expression profile in a sensory neuropathy model with cardiac diastolic dysfunction and aimed to identify key mRNA molecular targets of the differentially expressed miRNAs that may contribute to cardiac dysfunction. Methods: Male Wistar rats were treated with vehicle or capsaicin for 3 days to induce systemic sensory neuropathy. Seven days later, diastolic dysfunction was detected by echocardiography, and miRNAs were isolated from the whole ventricles. Results: Out of 711 known miRNAs measured by miRNA microarray, the expression of 257 miRNAs was detected in the heart. As compared to vehicle-treated hearts, miR-344b, miR-466b, miR-98, let-7a, miR-1, miR-206, and miR-34b were downregulated, while miR-181a was upregulated as validated also by quantitative real time polymerase chain reaction (qRT-PCR). By an in silico network analysis, we identified common mRNA targets (insulin-like growth factor 1 (IGF-1), solute carrier family 2 facilitated glucose transporter member 12 (SLC2a-12), eukaryotic translation initiation factor 4e (EIF-4e), and Unc-51 like autophagy activating kinase 2 (ULK-2)) targeted by at least three altered miRNAs. Predicted upregulation of these mRNA targets were validated by qRT-PCR. Conclusion: This is the first demonstration that sensory neuropathy affects cardiac miRNA expression network targeting IGF-1, SLC2a-12, EIF-4e, and ULK-2, which may contribute to cardiac diastolic dysfunction. These results further support the need for unbiased omics approach followed by in silico prediction and validation of molecular targets to reveal novel pathomechanisms.

STZ treatment induced apoptosis of retinal cells and effect of up-regulation of calcitonin gene related peptide in rats

BACKGROUND

Evidence indicates an early neural injury of the retinal cells in diabetes. The aim of the current study was to investigate the apoptosis of the retinal cells and the relationship with CGRP.

MATERIALS AND METHODS

The diabetes was induced by treatment of STZ, using which the apoptosis of retinal cells, the caspase-3 activity and the expression of CGRP in the retina and the serum were examined. Capsaicin (20mg/kg) was given to the animals to induce up-regulation of the CGRP. Apoptosis and CGRP in the retina were also examined in an in vitro study.

RESULTS AND CONCLUSION

The apoptosis of the retinal cells was confined to the GCL, in which CGRP was normally located. A significant increase in the apoptosis ratio (P<0.05) was observed in the STZ treated animals and high glucose incubated retina, with reductions of CGRP. The pre-treatment with capsaicin effectively up-regulated CGRP and its encoding mRNA and attenuated the cell apoptosis and caspase-3 activity in the retina. The increases of the cell apoptosis in the retina may be related to the down-regulation of endogenous CGRP in diabetes. Capsaicin may attenuate the apoptosis of the retina cells at early times of diabetes, via up-regulation of CGRP.

Endogenous alpha-calcitonin gene-related peptide mitigates liver fibrosis in chronic hepatitis induced by repeated administration of concanavalin A

BACKGROUND

Alpha-calcitonin gene-related peptide (alphaCGRP) is a 37-amino acid pleiotropic peptide that we previously showed to exert a hepatoprotective effect during concanavalin A (Con A)-induced acute hepatitis. In the present study, we used alphaCGRP(-/-) mice to further investigate the antifibrogenic and hepatoprotective effects of endogenous alphaCGRP in Con A-induced chronic hepatitis.

METHODS

Chronic hepatitis was induced in alphaCGRP(-/-) and wild-type mice by repeated administration of Con A. Serum transaminases were measured to assess hepatic injury. The severity of fibrosis and the activation of hepatic stellate cells (HSCs) were analysed by Masson trichrome staining and immunohistochemical staining of alpha-smooth muscle actin (alpha-SMA) respectively. Altered expression of fibrosis- and inflammation-related genes was evaluated using a quantitative real-time polymerase chain reaction. Activation and proliferation of HSCs were analysed using both primary cultured HSCs from the mice and the LI90 HSC cell line.

RESULTS

alphaCGRP(-/-) mice showed more severe liver fibrosis than wild-type mice in a Con A-induced chronic hepatitis model. In histological and gene expression analyses, alphaCGRP(-/-) mice showed greater inflammatory and fibrotic changes, greater HSC activation and a higher incidence of apoptosis among nonparenchymal cells than wild-type mice.

CONCLUSIONS

Endogenous alphaCGRP mitigates liver fibrosis in chronic hepatitis induced by repeated administration of Con A. alphaCGRP could be a useful therapeutic target for the treatment of chronic hepatitis.

Calcitonin gene-related peptide-evoked sustained tachycardia in calcitonin receptor-like receptor transgenic mice is mediated by sympathetic activity

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) are potent vasodilators and exert positive chronotropic and inotropic effects on the heart. Receptors for CGRP and AM are calcitonin receptor-like receptor (CLR)/receptor-activity-modifying protein (RAMP) 1 and CLR/RAMP2 heterodimers, respectively. The present study was designed to delineate distinct cardiovascular effects of CGRP and AM. Thus a V5-tagged rat CLR was expressed in transgenic mice in the vascular musculature, a recognized target of CGRP. Interestingly, basal arterial pressure and heart rate were indistinguishable in transgenic mice and in control littermates. Moreover, intravenous injection of 2 nmol/kg CGRP, unlike 2 nmol/kg AM, decreased arterial pressure equally by 18 ± 5 mmHg in transgenic and control animals. But the concomitant increase in heart rate evoked by CGRP was 3.7 times higher in transgenic mice than in control animals. The effects of CGRP in transgenic and control mice, different from a decrease in arterial pressure in response to 20 nmol/kg AM, were suppressed by 2 μmol/kg of the CGRP antagonist CGRP(8-37). Propranolol, in contrast to hexamethonium, blocked the CGRP-evoked increase in heart rate in both transgenic and control animals. This was consistent with the immunohistochemical localization of the V5-tagged CLR in the superior cervical ganglion of transgenic mice. In conclusion, hypotension evoked by CGRP in transgenic and control mice was comparable and CGRP was more potent than AM. Unexpectedly, the CLR/RAMP CGRP receptor overexpressed in postganglionic sympathetic neurons of transgenic mice enhanced the positive chronotropic action of systemic CGRP.

Effects of adrenomedullin 2 on regional hemodynamics in conscious rats

The present study aimed to assess the effects of rat adrenomedullin 2 on systemic and regional hemodynamics in conscious Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Intravenous infusion of rat adrenomedullin 2 (0.25-5 micro g/kg/min) decreased blood pressure, and increased heart rate in a dose-dependent manner in both types of rats. Rat adrenomedullin 2 (5 micro g/kg/min) increased heart rate and cardiac output. As a result, total peripheral resistance significantly decreased. In SHRs, adrenomedullin 2 significantly increased regional blood flow in the heart, liver, spleen, kidneys, and adrenal glands. Especially, effects on heart, liver, and kidneys were remarkable. Regional hemodynamic changes were reproduced in WKY rats, and there was no qualitative difference in regional responses to rat adrenomedullin 2 between SHRs and WKY rats. Thus, rat adrenomedullin 2 predominantly increased flow rates in organs that were richly blood-supplied from cardiac output. Rat adrenomedullin 2 may contribute to the regulation of the cardiovascular system, by acting as a local vasodilatory hormone as well as a circulatory hormone.

Cardiovascular effects

Amylin can lower blood pressure in anesthetized animals (in which reflex bradycardia is absent), or evoke reflex bradycardia. This effect is likely in response to vasodilatation mediated via calcitonin gene-related peptide (CGRP) receptors, and only occurs at concentrations two to three orders of magnitude higher than physiological amylin concentrations. There is suggestive, but not fully established, evidence for an amylin-like pharmacology with cardiotropic effects, consisting of inotropy (stimulation of contractility) and suppression of secretion of atrial natriuretic peptide (ANP).

Homologous desensitization of calcitonin gene-related peptide-induced relaxation in rat intramural coronary arteries

We investigated the type of desensitization of calcitonin gene-related peptide (CGRP)-induced responses in rat isolated intramural coronary arteries using isometric myograph and FURA-2 technique. In coronary arteries precontracted with 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F2alpha (U46619), development of tachyphylaxis to CGRP is characterized by significant attenuation of CGRP-induced maximal reduction in the tension and [Ca2+](i) during the second CGRP concentration-response curve; however, there was no further reduction in the CGRP-induced maximum relaxation during the third CGRP concentration-response curve. There was no sign of tachyphylaxis to CGRP when CGRP concentration-response curves were recorded in 36 mM K+-depolarized coronary arteries contrary to the results obtained in 300 nM U46619-precontracted coronary arteries. Preincubation with colchicine did not prevent the development of tachyphylaxis to CGRP in U46619-precontracted coronary arteries, indicating no role for endocytosis. Development of tachyphylaxis to CGRP was completely abolished by preincubating the coronary arteries with 1 microM RO 31-8220, indicating a role for protein kinases. Pre-exposure of the coronary arteries to isoprenaline or forskolin did not attenuate the CGRP-induced relaxation in these vessels, indicating that the cAMP-protein kinase A (PKA) pathway is not involved. Like CGRP, the coronary arteries developed tachyphylaxis toward isoprenaline during the second exposure. However, there was no sign of tachyphylaxis to either forskolin or dibutyryl cAMP (dbcAMP) during the second exposure. In conclusion, these results suggest that development of tachyphylaxis to CGRP in U46619-precontracted coronary is related to CGRP receptor-mediated activation of protein kinase.

The effect of adrenomedullin, amylin fragment 8-37 and calcitonin gene-related peptide on contractile force, heart rate and coronary perfusion pressure in isolated rat hearts

The effect of human adrenomedullin, human amylin fragment 8-37 (amylin 8-37) and rat calcitonin gene-related peptide (CGRP) on contractile force, heart rate and coronary perfusion pressure has been investigated in the isolated perfused rat hearts. Adrenomedullin (2x10(-10), 2x10(-9) and 2x10(-8) M) produced a significant decrease in contractile force and perfusion pressure, but only the peptide caused a decline in heart rate at the highest dose. Amylin (10(-9), 10(-8) and 10(-7) M) significantly increased and then decreased contractile force. Two doses of amylin (10(-8) and 10(-7) M) induced a significant increase in heart rate, however amylin did not change perfusion pressure in all the doses used. Rat alpha CGRP (10(-8), 10(-7) and 10(-6) M) evoked a slight decline in contractile force following a significant increase in contractile force induced by the peptide. CGRP in all the doses raised heart rate and lowered perfusion pressure. Our results suggest that adrenomedullin has negative inotropic, negative chronotropic and coronary vasodilator actions. Amylin produces a biphasic inotropic effect and evokes a positive chronotropy. CGRP causes positive inotropic, positive chronotropic and vasodilatory effects in isolated rat hearts.

Influence of calcitonin gene-related peptide release on pH-induced mechanical depression in rat atria

Rat atria is richly innervated by sensory nerve fibers that release CGRP when stimulated either by capsaicin or acid pH. We studied the physiological relevance of acid pH-induced CGRP release on changes in atrial contractility and relaxation produced by lowering the pH. Isolated atria electrically paced at 2.77 Hz were exposed to a 10-minute period of metabolic acidosis (pH=6.73+/-0.01, n=28) after: 1) CGRP release induced by capsaicin 0.5 microM; 2) blockage of CGRP release with ruthenium red (RR) 5 microM; 3) no pretreatment; and 4) CGRP receptor blockage with CGRP(8-37) 1 microM. Contractility and relaxation were significantly less depressed by acid pH when CGRP release was prevented by RR or CGRP receptor activation was blocked by CGRP(8-37). The results suggest that CGRP release and the activation of CGRP receptors may be physiologically involved in contributing to the depression of contractility and relaxation induced by acid pH in rat atria.

Functional and biochemical evidence for capsaicin-induced neural endothelin release in isolated working rat heart

In isolated working rat heart, capsaicin elicited a concentration-dependent constriction of coronary arteries accompanied by decline of all cardiac parameters recorded (heart rate, coronary and aortic flow, left ventricular developed pressure, and first derivative of left ventricular developed pressure). The following evidence suggests that capsaicin-induced changes are mediated by endothelin of neural origin: (1) the capsaicin (10 nM)-evoked decrease in coronary flow resulting in deterioration of cardiac functions was mimicked by endothelin (0.1 nM); (2) the selective endothelin ET(A) receptor antagonist, cyclo (D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl) (1 microM), abolished the cardiac effects provoked by capsaicin (10 nM); (3) reduction of extracellular Ca2+ concentration from 2.4 to 1.2 or 0.6 mM inhibited the cardiac effects of capsaicin (10 nM) but not those induced by endothelin (0.1 nM); (4) perfusion of the heart with 0.1% (v/v) Triton X-100 damaged the endothelium and reversed the enhancement of coronary flow evoked by bethanechol (1 microM), decreased the basal flow, but was without effect on capsaicin-induced coronary constriction; (5) in response to capsaicin challenge (10-100 nM), the endothelin concentration measured in coronary effluent by means of radioimmunoassay increased up to sevenfold but remained unchanged in the presence of 0.6 mM Ca2+; (6) no reduction of coronary flow was induced by capsaicin (100 nM) applied to the heart of rats which were desensitised by capsaicin (150 mg/kg). It is concluded that, in the rat heart, capsaicin acting on VR1 capsaicin receptors elicits a release of endothelin from the sensory nerve terminals.

Mechanism of CGRP-induced relaxation in rat intramural coronary arteries

1. This study investigates the mechanism of CGRP-induced relaxation in intramural coronary arteries by determining the effect of CGRP on cytosolic Ca(2+) concentration ([Ca(2+)](i)) using FURA-2 technique. 2. CGRP concentration-dependently (10 pM - 100 nM) decreased the [Ca(2+)](i) and tension of coronary arteries precontracted with either U46619 or BAY K 8644, and also of resting coronary arteries in PSS. In 36 mM K(+)-depolarized arteries, CGRP reduced only the tension without affecting the [Ca(2+)](i). 3. In 300 nM U46619- precontracted arteries, pretreatment with 10 microM thapsigargin significantly (P<0.05) attenuated the CGRP-induced reduction in the tension (but not [Ca(2+)](i)). 4. In 300 nM U46619-precontracted arteries, pretreatment with either 100 nM charybdotoxin or 100 nM iberiotoxin or 10 nM felodipine significantly (P<0.05) attenuated the CGRP-induced reduction in both [Ca(2+)](i) and tension. In contrast, 1 microM glibenclamide did not affect the CGRP-induced responses in these coronary arteries. 5. In resting coronary arteries, only pretreatment with the combination of 1 microM glibenclamide and 100 nM charybdotoxin attenuated the CGRP-induced decrease in the [Ca(2+)](i) and tension, suggesting a different mechanism of action for CGRP in resting coronary arteries. 6. We conclude that CGRP relaxes precontracted rat coronary arteries via three mechanisms: (1) a decrease in [Ca(2+)](i) by inhibiting the Ca(2+) influx through membrane hyperpolarization mediated partly by activation of the large conductance Ca(2+)-activated potassium channels, (2) a decrease in [Ca(2+)](i) presumably by sequestrating cytosolic Ca(2+) into thapsigargin-sensitive Ca(2+) storage sites and (3) a decrease in the Ca(2+)-sensitivity of the contractile apparatus. In resting coronary arteries, however, there seems to be an interplay between different types of K(+) channels.

Non-competitive antagonism of amylin on CGRP(1)-receptors in rat coronary small arteries

We examined the interaction between rat-amylin and relaxations induced by rat-alphaCGRP and isoprenaline in rat isolated coronary small arteries. Amylin, 0.1 - 100 nM, had a concentration dependent non-competitive antagonistic effect on rat-alphaCGRP-induced responses with an EC(50) of approximately 1 nM. Amylin did not affect the relaxations induced by isoprenaline at a concentration of 10 nM. The apparent equilibrium dissociation constant, K(A), for CGRP(1)-receptors in the rat coronary small arteries was approximately 2 nM. Analysis of the relationship between receptor occupancy and response to rat-alphaCGRP indicates that the receptor reserve is small. Our results show that amylin in low concentrations acts as a selective non-competitive inhibitor at CGRP(1)-receptors in rat isolated coronary small arteries.

Modulation of coronary flow and cardiomyocyte size by sensory fibers

Cardiac tissue is densely innervated by sensory neurons that are believed to play important modulatory roles in cardiac functions. In this study, pretreatment of neonate rats with capsaicin was performed. In adult rats, cardiomyocyte size and amount of fibrous tissue in left ventricles as well as in vitro coronary flow were evaluated. The chronotropic and inotropic responses to beta-adrenoceptor agonists (norepinephrine and isoproterenol), muscarinic agonists (carbachol and pilocarpine), and calcitonin gene-related peptide (CGRP) were also investigated with the use of the isolated right atria preparation. Capsaicin pretreatment significantly (P<0.05) reduced both basal coronary flow (18% reduction) and cardiomyocyte size (34% reduction) without affecting the amount of fibrous tissues in the left ventricles. The positive inotropic and chronotropic effects in response to norepinephrine in the isolated rat heart did not significantly differ between control and capsaicin-treated rats. Similarly, the positive chronotropic effects in response to norepinephrine, isoproterenol, and CGRP as well as the negative chronotropic responses to carbachol and pilocarpine in the isolated right atria were not affected by capsaicin pretreatment. Our data are consistent with the suggestion that reductions of both basal coronary flow and cardiomyocyte size seen in hearts from capsaicin-pretreated rats may be consequences of CGRP depletion. The cardiomyocyte size reduction produced by capsaicin treatment may be related to a modulatory role of CGRP as a growth factor.

Interplay between nitric oxide and CGRP by capsaicin in isolated guinea-pig heart

Capsaicin at a concentration of 10(-7)m induced a significant increase in heart rate and increased coronary flow in isolated Langendorff-perfused guinea-pig hearts. This effect was completely blocked by 30 microm of N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase. Additional incubation with 3 m m L-Arg antagonized the inhibitory effect of L-NAME. In the presence of 1 microm of a human calcitonin gene-related peptide fragment (hCGRP 8-37), a CGRP-receptor antagonist, L-Arg was without effect. We conclude that a capsaicin-induced increase in coronary flow and heart rate is dependent from an interplay between CGRP and NO in guinea-pig hearts. 1999 Academic Press.

Aggravation of myocardial infarction in the porcine heart by capsaicin-induced depletion of calcitonin gene-related peptide (CGRP)

The potent vasodilator calcitonin gene-related peptide (CGRP) is stored in a population of C-fiber afferents that are sensitive to capsaicin. CGRP has been suggested to have a beneficial effect in myocardial ischemia. In this study we used capsaicin pretreatment to deplete cardiac C-fiber peptide stores and tried to evaluate the role of endogenous CGRP in myocardial ischemia. Six pigs were pretreated with capsaicin (50 mg/kg). Forty-eight hours later, they were subjected to 40min occlusion of the left anterior descending coronary artery. After 4 h of reperfusion, the heart was excised, and the extent of myocardial infarction was measured by using triphenyl tetrazolium chloride. Content of CGRP in the ischemic and the nonischemic myocardium was measured by radioimmunoassay. Capsaicin-treated pigs had more extensive myocardial infarction (56+/-6% vs. 26+/-8% of the area at risk; p=0.013) and a lower myocardial content of CGRP (14+/-6 vs. 32+/-5 pmol/g; p=0.039) compared with six untreated control pigs. Furthermore, capsaicin-treated pigs had significantly increased mean arterial blood pressure compared with controls. This study indicates that peptides released from cardiac C fibers have a beneficial effect in myocardial ischemia and reperfusion. In view of its potent effects in cardiovascular regulation, CGRP is a possible candidate for the mediation of the observed cardioprotective effect.

Caliber dependent calcitonin gene-related peptide-induced relaxation in rat coronary arteries: effect of K+ on the tachyphylaxis

The influence of vessel caliber on rat calcitonin gene-related peptide (rat-alphaCGRP)-induced responses and the reproducibility of rat-alphaCGRP concentration-response curves were investigated in the left intramural coronary artery of Sprague-Dawley rats. Rat-alphaCGRP (10(-11)-10(-7) M) induced concentration-dependent relaxations with a pD2-value equal to 8.43 +/- 0.05 (n = 44) and maximal relaxation equal to 52 +/- 3% (n = 44). Both the maximal relaxation and the sensitivity to rat-alphaCGRP were significantly and inversely correlated with vessel lumen diameter. The coronary arteries developed tachyphylaxis in response to rat-alphaCGRP, which was concentration dependently decreased by activating the vessels twice with a buffer containing 36 or 125 mM K+. The rat-alphaCGRP-curve became fully reproducible after activation of the arteries twice with 125 mM K+. These results indicate a caliber-related dependency of both the effect of and sensitivity to rat-alphaCGRP in intramural rat coronary arteries because the arteries become more sensitive and reactive to rat-alphaCGRP with decreasing caliber. Tachyphylaxis can be avoided by repeated activation with 125 mM K+.

Positive chronotropic and inotropic effects of C-type natriuretic peptide in dogs

We have recently reported that C-type natriuretic peptide (CNP) has a positive chronotropic effect in dogs. We further investigated the effect of CNP on canine cardiac functions: 1) in situ, by exploring the effects of isoproterenol (10 microg), angiotensin II (ANG II, 5 microg), and CNP (40 microg) injections (n = 8) on computerized epicardial mapping of atrial activation to detect a shift in pacemaker location; 2) by examining the presence of natriuretic peptide receptor (NPR)-A and -B mRNAs in atrial and nodal tissues using semiquantitative reverse-transcription polymerase chain reaction; 3) in vitro, using spontaneously beating right atrial preparations (n = 6), by recording the transmembrane potentials of sinoatrial node (SAN) cells before and after injection of CNP (25 microg); and 4) by observing the effects of CNP (25 microg) on contractile force of paced isolated right atrial preparations (n = 6). The results indicate that 1) the site of earliest extracellular electrical activation in the SAN remains mostly unchanged in response to CNP, whereas it shifts to the superior region of the SAN after isoproterenol and ANG II injections; 2) NPR-A and -B mRNAs are present in atrial and nodal tissues; 3) CNP significantly increases the maximal rate of diastolic depolarization and decreases the action potential duration at 75 and 90% of repolarization; and 4) CNP significantly increases atrial contractile force. These results suggest that CNP modifies cardiac ionic currents to produce positive chronotropic and inotropic effects by stimulation of NPR-B receptors, located in the SAN region, and that CNP plays a role in the modulation of cardiac function.

Prejunctional modulation by nociceptin of nerve-mediated inotropic responses in guinea-pig left atrium

The superimposition of a train of electrical stimuli (15 Hz. 1 ms, 60 V for 2.5 s) to the electrically driven (3 Hz) isolated left atria from reserpine-pretreated guinea pigs in the presence of atropine (1 microM) produces a delayed positive inotropic response due to the antidromic activation of capsaicin-sensitive primary afferents and the release of the sensory neuropeptide, calcitonin gene-related peptide (CGRP). The novel opioid peptide nociceptin, inhibited (Emax 88% inhibition at 1 microM) in a concentration-dependent manner (10 nM-1 microM) (EC50 33 nM) the delayed positive inotropic response induced by train electrical field stimulation, without affecting the positive inotropic response produced by exogenous CGRP (10 nM) or capsaicin (30 nM). The inhibitory effect of nociceptin on the delayed positive inotropic response induced by train electrical field stimulation was not antagonized by the opioid receptor antagonists naloxone, naltrindole and nor-binaltorphimine (1 microM each) nor was it modified by a cocktail of peptidase inhibitors (bestatin, captopril and thiorphan, 1 microM each). A significant inhibition by nociceptin (1 microM) was also observed toward the sympathetic positive inotropic response produced by EFS at 5 Hz in the presence of atropine (1 microM) and after in vitro capsaicin desensitization and toward the parasympathetic negative inotropic response produced by EFS at 10 Hz in atria from reserpine-pretreated guinea pigs and after in vitro capsaicin desensitization. We conclude that nociceptin exerts a prejunctional inhibitory effect on evoked release of CGRP from capsaicin-sensitive sensory nerve terminals in guinea-pig left atria. The effect of nociceptin occurs independently from the activation of mu-, delta- or kappa-opioid receptors. Nociceptin, at appropriate frequency of stimulation, appears to exert a general inhibitory neuromodulation on transmitters release in guinea-pig left atria.

The characteristics in the inhibitory effects of capsaicin on voltage-dependent K(+) currents in rat atrial myocytes

The electrophysiological effects of capsaicin in rat atrial myocytes were examined. Measurement of contractile force was done in rat left atria. Whole-cell patch-clamp technique was primarily used to study the change in membrane potential and ionic currents. Capsaicin produced an initial rise and a sustained increase in contractile force in rat left atria. Capsaicin (10 μM) caused a significant prolongation of atrial action potential. In voltage-clamp experiments, capsaicin (1-100 μM) caused the reversible reduction in the amplitude of transient outward (I(TO)) and late outward (I(L)) K(+) currents in concentration- and voltage-dependent manners. The time course for inactivation of I(TO) was changed to the biexponential process after the application of capsaicin. Capsaicin failed to cause any significant shift in quasi-steady-state inactivation curve of I(TO). The EC(50) values for the inhibitory effects of capsaicin on I(TO) and I(L) were 5 and 20 μM, respectively. Capsaicin also suppressed the amplitude of acetylcholine- or adenosine-induced K(+) current, i.e., I(K(ACh,Ado)). The EC(50) value for capsaicin-mediated inhibition of I(K(ACh,Ado)) is 50 μM. The present findings suggest that in isolated rat atria, during capsaicin exposure, the capsaicin-mediated inhibition of these K(+) channels is one of the ionic mechanisms underlying the positive inotropic and chronotropic actions.

The role of substance P in myocardial dysfunction during ischemia and reperfusion

Impairment of myocardial contraction ("myocardial stunning") occurs during reperfusion after short ischemic periods. Substance P (SP) is widely distributed in heart and can be released by various stimuli including myocardial hypoxia. Our previous study shows SP has a negative inotropic effect in guinea pig heart. The objective of this study was to investigate whether SP contributes to the myocardial stunning after brief global ischemia. Guinea pig hearts in a Langendorff preparation were subjected to 15 min of global ischemia followed by 60 min reperfusion. Experiments were performed without and with pretreatment with neurokinin-1 (NK1) receptor antagonists, spantide (10(-6)M) or CP-99,994-01 (10(-6)M) in order to study the role of SP. Experiments were also performed in hearts which were perfused with atropine, phentolamine, and nadolol (10(-6)M each) to examine the role of neurotransmitters and autonomic receptors. A group of hearts obtained from capsaicin-pretreated guinea pigs was also investigated. Left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), heart rate, and perfusion pressure were monitored. At the end of reperfusion, the LVDP of control hearts recovered to only 55 +/- 6% (+/- SEM) of preischemic baseline and the LVEDP increased significantly (P > 0.05). With pretreatment with spantide or CP-99,994-01, LVDP recovered to 88 +/- 2% or 78 +/- 2% of the preischemic baseline, respectively. The LVEDP of these hearts was not different from preischemic baseline and much smaller than in control hearts. There were no differences in heart rate and perfusion pressure compared to baseline among all groups. Similar results were obtained in hearts perfused with autonomic blockers. However, recoveries of LVDP and LVEDP were faster in hearts perfused with autonomic blockers during the first 10 min of reperfusion. Pretreatment with capsaicin also significantly improved recovery of LVDP and LVEDP. In conclusion, substance P is involved in postischemic myocardial dysfunction and neurokinin-1 receptors mediate this action. The NK1 receptor antagonists may be useful in prevention of "myocardial stunning".

Multiple sensory and functional effects of non-phenolic aminodimethylene nonivamide: an approach to capsaicin antagonist

1. Hexylaminodimethylene nonivamide (CAPCNC6, 0.1-10 microM) inhibited the contractility of isolated guinea pig right atria, toxically revealed positive inotropic, chronotropic and then a cardiac arrest effect at 100 microM and inhibited capsaicin (1.0 microM)-induced cardiotonic effects. 2. CAPCNC6 (0.1-10 microM)-induced aorta contractions were inhibited in the presence of flunarizine, atropine, phentolamine, Ca(2+)-free solution and pre-treatment of the animal with capsaicin. 3. CAPCNC6 (1.0-300 microM)-induced trachea contractions were inhibited in the presence of capsazepine, ruthenium red, hCGRP8-37 and pre-treatment of the animal with capsaicin.

Bradykinin B2 receptor-mediated chronotropic effect of bradykinin in isolated guinea pig atria

The present study was undertaken to characterize the direct chronotropic effect of bradykinin in isolated spontaneously beating atria of the guinea pig. Bradykinin caused concentration-dependent increases in the beating rate of atria. In contrast, the active metabolite of bradykinin and the typical bradykinin B1 receptor agonist, Des-Arg9-bradykinin, had no effect on the beating rate of atria. Inhibition of converting enzyme or neutral endopeptidase by captopril or SQ-28603, respectively, did not affect beating rate but potentiated bradykinin-induced increase in beating rate. The potent bradykinin B2 receptor antagonist, HOE 140, antagonized bradykinin-induced chronotropic effect. In contrast, the bradykinin B1 receptor antagonist, Lys-[Leu8]Des-Arg9-bradykinin, had no effect. The increase in beating rate caused by bradykinin was not affected by blockade of beta 1-adrenoceptors, cyclooxygenase, or nitric oxide synthesis using atenolol, indomethacin and N omega-nitro-L-arginine, respectively. Unlike bradykinin, angiotensin I and angiotensin II caused very small or no change in beating rate in the presence or absence of captopril and SQ-28603. These results indicate that bradykinin causes a direct positive chronotropic effect which is mediated by activation of bradykinin B2 receptors independently of prostaglandins and beta 1-adrenoceptors.

The role of the sensory peptide calcitonin-gene-related peptide(s) in skeletal muscle carbohydrate metabolism: effects of capsaicin and resiniferatoxin

1. The content of calcitonin-gene-related-peptide-like immunoreactivity (CGRP-LI) in various rat muscles was measured. Starvation for 24 h did not affect the content of CGRP-LI in these muscles, except for a decreased level in the starved-rat diaphragm. Higher contents of CGRP-LI were observed in well-vascularized muscles. 2. Capsaicin (at 1, 10 and 100 microM) inhibited insulin-stimulated rates of glycogen synthesis in isolated stripped incubated soleus muscle preparations by a mechanism independent of catecholamine release, since the effects of capsaicin were not altered by the beta-adrenoreceptor antagonist DL-propranolol. 3. Resiniferatoxin (10 nM), which is a potent capsaicin agonist, also significantly inhibited the insulin-stimulated rate of glycogen synthesis. Furthermore, the concentration of resiniferatoxin required to inhibit glycogen synthesis was 100 times less than the concentration of capsaicin needed for the same effect. 4. Capsaicin (10 microM) decreased the content of CGRP-LI in isolated stripped incubated soleus muscle preparations by about 40%. 5. Neonatal treatment of rats with capsaicin, which causes de-afferentation of some sensory nerves such, we hypothesize, that CGRP can no longer be released to counteract the effects of insulin in vivo, caused increased rates of glycogen synthesis and increased glycogen content in stripped soleus muscle preparations in vitro when muscles were isolated from the adult rats. 6. These findings support the hypothesis that capsaicin and resiniferatoxin elicit an excitatory response on sensory nerves in skeletal muscle in vitro to cause the efferent release of CGRP. Consequently, CGRP is delivered to skeletal muscle fibres to inhibit insulin-stimulated glycogen synthesis. The role of CGRP in recovery of blood glucose levels during hypoglycaemia is discussed.

Effects of a synthetic rat adrenomedullin on regional hemodynamics in rats

The effects of rat adrenomedullin, a novel vasorelaxant peptide, on systemic and regional hemodynamics were examined in conscious Sprague Dawley (SD) rats and spontaneously hypertensive rats (SHR). The intravenous infusion of adrenomedullin at rates of 1.67 and 5 micrograms/kg per min decreased the mean arterial pressure in a dose-dependent fashion in both types of rats. Adrenomedullin at a rate of 5 micrograms/kg per min increased the heart rate and cardiac output. As a result, the total peripheral resistance significantly decreased. With regards to the regional hemodynamics, adrenomedullin significantly increased the flow rates in the lungs, heart, spleen, kidneys, adrenal glands and small intestine of SHR. The flow rates in the brain and skin did not change and the flow rates in the skeletal muscle and testis were decreased. These regional hemodynamic changes were also observed in SD rats and there was no qualitative difference in the regional responses to adrenomedullin between SHR and SD rats. Thus, adrenomedullin predominantly increased the flow rates in organs in which adrenomedullin gene was highly expressed. It therefore seems that adrenomedullin may act as a local vasodilatory hormone rather than as a circulatory hormone.

Inhibitory effects of capsaicin on acetylcholine-evoked responses in rat phaeochromocytoma cells

1. The effects of capsaicin on cellular responses evoked by acetylcholine (ACh) and those by adenosine 5'-triphosphate (ATP) were investigated in rat phaeochromocytoma PC12 cells. 2. Capsaicin (1 to 30 microM) suppressed dopamine release and the intracellular Ca2+ increase evoked by 100 microM ACh. The concentration-dependence of the ACh-evoked release of dopamine was not shifted but the maximal response was reduced by capsaicin. Dopamine release evoked by 80 mM KCl was also suppressed by capsaicin (3 and 30 microM), but the extent of suppression was smaller than that of the ACh-evoked release. 3. Under whole-cell voltage-clamp, capsaicin (1 to 30 microM) reversibly inhibited the inward current activated by ACh (30 to 300 microM). The inhibition exhibited dependence on the concentration of ACh, and the current activated by a higher concentration of ACh was less inhibited. Voltage-dependence of block by capsaicin was not observed when it was tested either by applying a ramp pulse during the current activation by ACh or by eliciting the current in cells held at various potentials. 4. High concentrations of capsaicin (30 to 100 microM) enhanced the inward current as well as dopamine release evoked by 30 microM ATP. 5. The results suggest that low concentrations of capsaicin selectively antagonize responses mediated by nicotinic receptor-channels without affecting those mediated by purinoceptor-coupled channels. As the antagonism by capsaicin of the ACh-evoked responses was observed at concentrations as low as 1 microM, the influence on nicotinic receptors should be taken into account when this compound is used as a pharmacological tool to deplete neuropeptides.

Distribution of calcitonin gene-related peptide-like immunoreactivity in the bovine conduction system: correlation with substance P

The role of calcitonin gene-related peptide (CGRP) in the heart conduction system is unclear. In the present study, the distribution of CGRP in relation to that of substance P (SP) was examined in the bovine conduction system using immunohistochemical methods. Varicose nerve fibres showing CGRP-like immunoreactivity (LI) were frequently observed in the nerve fascicles, some of these fibres often also showing SP-LI. A few fibres exhibiting CGRP-LI were also observed in the intrinsic ganglia. In blood vessel walls and particularly in the conduction tissue, i.e., in association with the nodal cells and the Purkinje fibres, there were only a few varicose fibres showing both CGRP- and SP-LI, whilst there was a large number of varicose fibres showing only SP-LI. The observations show that the main morphologic correlate for the occurrence of CGRP-effects in the bovine conduction system is varicose nerve fibres located in the nerve fascicles. The observations also suggest that CGRP has effects at the intrinsic ganglia and that SP predominates over CGRP in the innervation of blood vessel walls and the conduction tissue.

Innervation of the pacemaker in guinea-pig sinoatrial node

Heart rate is regulated by the autonomic nervous system but little is known about the pattern of innervation of the pacemaker in the sinoatrial node, or the subpopulations of nerves involved. Therefore in this study the pacemaker was located using electrophysiological methods and the pattern of innervation established by cholinesterase staining. In subsequent experiments, subpopulations of sympathetic, sensory and parasympathetic nerves were identified. Sympathetic nerves were labelled by glyoxylic acid-induced catecholamine fluorescence or an antiserum raised against tyrosine hydroxylase (TH). These experiments showed that the entire sinoatrial node was densely innervated by sympathetic axons, the majority of which were immunoreactive for neuropeptide Y (NPY). There were a few axons which were only immunoreactive for TH. Sensory nerves which were immunoreactive for both substance P (SP) and calcitonin gene-related peptide (CGRP) were also found throughout the sinoatrial node. In the absence of a selective marker for parasympathetic neurons, hearts were extrinsically denervated by placing them in organotypic culture to allow degeneration of extrinsic axons. In this way intrinsic parasympathetic neurons could be characterised. These experiments revealed several distinct populations of parasympathetic nerves which innervated only a small, discrete part of the sinoatrial node. These populations were immunoreactive for NPY, somatostatin (SOM) or vasoactive intestinal peptide (VIP) alone, or SOM combined with NPY, SOM with dynorphin B, and SOM with SP. These results highlight a remarkable difference in the pattern of innervation of the sinoatrial node by the sympathetic and parasympathetic nervous systems. Furthermore the presence of several distinct populations of autonomic cardiac neurons indicates a further complexity in neuronal regulation of heart rate.

Characterization of the CGRP receptor and mechanisms of action in rat mesenteric small arteries

Rat alpha-calcitonin gene-related peptide-induced concentration-dependent (100 pM-10 nM) relaxations in rat mesenteric small arteries (i.d. approximately 220 microns) contracted with noradrenaline, prostaglandin F2 alpha or K+, however, the maximal relaxation depended on the precontractile stimulus, being highest (95%) in arteries contracted with PGF2 alpha and lowest (51%) in arteries contracted with 125 mM K+. The relaxation was inhibited between 10 pM and 1 nM by removal of the endothelium, but was not antagonized by glibenclamide (1 microM), tetraethylammonium (30 mM), apamine (0.3 microM) and 4-aminopyridine (3 mM). The concentration-response curve to rat alpha-CGRP and human beta-CGRP was shifted to the right in the presence of 1 microM human alpha-CGRP(8-37) indicating a receptor affinity, -log(KB[M]), equal to 7.2 and 7.0, respectively. It is concluded that the relaxation induced by CGRP depends minimally on the endothelium and K(+)-channel opening is not a principal process in the relaxing effect of CGRP, thus a third mechanism must mediate the relaxation in these vessels. The main CGRP receptor type mediating relaxation in rat mesenteric small arteries belongs to the CGRP1 subtype.

Autonomic and sensory cardiovascular activities of nonivamide: intrathecal administration of clonidine

The effects of nonivamide on the cardiovascular system were examined and compared with the effects of substance P (SP) in rats. Intravenous (i.v.) injection (10 micrograms/kg) of nonivamide produced triphasic pressure responses (A; depressor, B; pressor, and C; depressor) and biphasic bradycardia responses (f; fast bradycardia and s; slow bradycardia). IA injection (10 micrograms/kg) into the epigastric artery caused hypotension and mild tachycardia. The effects of atropine, vagotomy, SP antagonist, propranolol, and clonidine on these responses were examined and mechanisms responsible for the nonivamide-induced responses are postulated as follows. A and f are due to vagal reflex resulting from the excitation of afferent sensory neurons in the heart and are parasympathetic efferent effects from the nucleus solitarius. B is involved in sympathetic activation, partly caused by the release of SP in the spinal cord. C is due to the vasodilatory effect of SP released from perivascular stores. s was diminished by vagotomy and is due to the bradycardiac effect of acetylcholine, released by SP, from cardiac stores. The activation of the autonomic system is inhibited by clonidine and involved in the wide spectrum of nonivamide-induced cardiovascular effects.

An adrenomedullin (ADM) fragment retains the systemic vasodilator activity of human ADM

The present study was undertaken to investigate the effects of human ADM, a newly discovered peptide present in normal human plasma, as well as a fragment of human ADM, human ADM13-52, on systemic hemodynamics in the anesthetized cat. Intravenous (i.v.) bolus injections of human ADM and human ADM13-52 decreased systemic arterial pressure (SAP) in a dose-dependent manner. Since neither peptide altered cardiac output, the decreases in SAP reflect reductions in systemic vascular resistance. The systemic vasodilator responses to the same doses of human ADM and human ADM13-52 in the cat were similar. The present study demonstrates the systemic vasodilator activity of ADM is conserved across species. The present data suggest that human ADM13-52 or a peptide structurally similar to it may mediate the hemodynamic properties of ADM in vivo in man. Since cardiac output and heart rate were not altered during the marked systemic vasodepressor response to ADM, activation of the ADM vasodilator mechanism may represent a therapeutic alternative in the clinical management of hypertensive diseases.

Calcitonin gene-related peptide-like immunoreactive (CGRPI) elements in the circadian system of the mouse: an immunohistochemistry combined with retrograde transport study

This study was based on immunohistochemical detection of calcitonin gene-related peptide-like immunoreactive (CGRPI) neurons and fibers in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL) of the mouse. CGRPI neurons and fibers were found within the ventrolateral part of the SCN, in the whole extent of IGL and sparsely distributed in ventral lateral geniculate body. The presence of CGRPI structures in the SCN and IGL of the mouse further supports the hypothesis of differences in the content of neuroactive substances in the circadian clock between mammalian species. Fluorogold retrograde transport combined with CGRP immunofluorescence demonstrates that CGRPI neurons in the IGL constitute a part of IGL reciprocal connections.

Nitric oxide is not involved in the effects induced by non-adrenergic non-cholinergic stimulation and calcitonin gene-related peptide in the rat mesenteric vascular bed

The mechanism involved in the effects induced by the activation of perineural non-adrenergic non-cholinergic (NANC) nerves or by exogenous calcitonin gene-related peptide (CGRP) was investigated in the rat mesenteric vascular bed (MVB) perfused with Kreb's solution containing methoxamine and guanethidine. The activation of NANC terminals of the tissue was carried out by means of electrical field stimulation (EFS). An increase in the perfusion pressure of the preparations was observed in the presence of two inhibitors of nitric oxide synthase: NG-monomethyl-L-arginine (L-NMMA) (100 microM) and NG-nitro-L-arginine methyl ester (L-NAME) (100 microM). However L-NMMA and L-NAME did not modify the relaxant effect induced by EFS and exogenous CGRP. Furthermore the relaxant effect induced by EFS and exogenous CGRP was not affected by the removal of endothelium from the preparations. These results provide evidence that the vasodilation induced by NANC stimulation or by exogenous CGRP in MVB does not involve NO production.

Calcitonin gene-related peptide gene expression in the spontaneously hypertensive rat

Calcitonin gene-related peptide, a product of the calcitonin gene, is a potent vasodilator neuropeptide. We have demonstrated that dietary calcium deficiency decreased the neuronal (laminae I/II of the dorsal horn of the spinal cord) content of immunoreactive calcitonin gene-related peptide in the normal rat. Neuronal calcitonin gene-related peptide levels are also reduced in the spontaneously hypertensive rat, a model characterized by calcium deficiency. However, the mechanism of this reduction in neuronal calcitonin gene-related peptide could be due to decreased synthesis or increased release. To determine if neuronal calcitonin gene-related peptide messenger RNA (mRNA) levels are also decreased in the spontaneously hypertensive rat, we measured relative calcitonin gene-related peptide mRNA levels (using a genomic hybridization probe specific for alpha- and beta-calcitonin gene-related peptide mRNA) in dorsal root ganglia from spontaneously hypertensive and Wistar-Kyoto control rats. Dorsal root ganglia neuronal cell bodies are a prominent site of calcitonin gene-related peptide synthesis and send axons to peripheral blood vessels and central spinal cord sites (laminae I/II). After normalization of calcitonin gene-related peptide mRNA levels of 18S RNA, the calcitonin gene-related peptide mRNA/18S RNA ratio was significantly decreased approximately threefold in the spontaneously hypertensive rats compared with controls. This alteration in calcitonin gene-related peptide mRNA levels is specific for dorsal root ganglia, because no strain differences in calcitonin gene-related peptide mRNA content were detected in heart or brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-adrenergic non-cholinergic (NANC) neural control of the atrial myocardium

1. Current concepts in the regulation of atrial contractility by non-adrenergic non-cholinergic (NANC) sensory nerves are reviewed. 2. There is now evidence that in addition to sympathetic and parasympathetic innervation capsaicin-sensitive sensory nerves contribute to the local control of atrial contractility by releasing NANC transmitters, such as calcitonin gene-related peptide (CGRP). 3. Certain chemical and physical stimuli affect atrial contractility by inducing the release of CGRP from sensory nerves. In addition, as widely recognized for the sympathetic and vagal atrial innervation, NANC neurotransmission is under the inhibitory control of several endogenous modulators. 4. Cardioexcitatory actions of NANC neurotransmission on the atrial myocardium are considered. 5. Pharmacological modulation of NANC neurotransmission and functional evidence for cross-talk between NANC and sympathetic neurones are also discussed.

The effects of neonatal capsaicin on plasma levels and tissue contents of CGRP

Tissue contents and plasma levels of IR-CGRP were studied following administration of capsaicin to newborn rats. A depletion of > 50% of IR-CGRP content was seen in the cardiovascular tissues (e.g., heart and peripheral arteries), lungs, gastrointestinal tract (e.g., esophagus, stomach, and intestine), genitourinary tract (e.g., ureter, bladder, uterus, and penis), and in the nervous system (e.g., dorsal root and trigeminal ganglia, sciatic and trigeminal nerves, and dorsal spinal cord) in capsaicin-treated rats, in comparison with the control rat tissues (p < 0.01). These findings are compatible with the known involvement of capsaicin of the unmyelinated sensory C and A delta fibers and hence their distribution in the nervous system and other organs. Plasma IR-CGRP levels were also significantly lower in the capsaicin-treated rats throughout their life span (p < 0.001), suggesting that, at least in part, circulating CGRP is derived from the nervous system. RP-HPLC confirmed the identity of CGRP in both tissue and plasma extracts.

Effects of capsaicin and 5-HT3 antagonists on 5-hydroxytryptamine-evoked release of calcitonin gene-related peptide in the guinea-pig heart

1. The effect of 5-hydroxytryptamine (5-HT) on the release of calcitonin gene-related peptide (CGRP) was studied directly in the isolated perfused heart and indirectly in the isolated left atria of guinea-pig. 2. 5-HT injection into the guinea-pig isolated and perfused heart evoked a dose-dependent (1-100 microM) release of CGRP-like immunoreactivity (LI) that was abolished by in vitro pretreatment with capsaicin and was not affected by indomethacin. 3. Chlorophenyldiguanide (CPD, 100 microM), but not 8-hydroxy-dipropylaminotetralin (8-OH-DPAT, 100 microM), sumatriptan (100 microM) or 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, 100 microM) evoked a release of CGRP-LI. Ondansetron (10 microM) or ICS205-930 (20 microM) completely abolished the 5-HT (100 microM)-evoked CGRP-LI release. 4. In the isolated electrically driven left atria of the guinea-pig 5-HT (1-10 microM) and CPD (3-100 microM) produced a positive inotropic response, which was abolished by capsaicin pretreatment. 8-OH-DPAT (10 microM) and DOI (10 microM) were inactive. Ondansetron inhibited the response to 5-HT with a pA2 of 6.50 (CL 6.08-6.91). 5. It is concluded that 5-HT causes a release of CGRP in the whole heart and a positive inotropic response in the isolated atria of guinea-pig. Both these effects are sensitive to capsaicin pretreatment and to 5-HT3 antagonists.

Localization and characterization of calcitonin gene-related peptide mRNA in rat heart

Calcitonin gene-related peptide (CGRP), a product of the calcitonin/CGRP gene, is a potent vasodilating neuropeptide widely distributed throughout the cardiovascular system, particularly in the heart. Immunocytochemical studies have demonstrated CGRP-containing neurofibrils in the myocardium and in the periadventitia of coronary blood vessels. Based on these studies, it has been assumed that all of the CGRP peptide in the heart is synthesized in neurons whose cell bodies are located outside of the heart. Using Northern blot analysis and a ribonuclease protection assay, we observed in the rat heart low levels of a CGRP-like mRNA species that appeared to be identical to authentic CGRP mRNA produced in the brain and dorsal root ganglia. The ventricles contained somewhat more CGRP mRNA than did the atria. Also, whereas the dorsal root ganglia synthesized both alpha- and beta-CGRP mRNA, only the alpha-CGRP mRNA was detected in the heart. The presence of CGRP mRNA in the heart suggests that the CGRP gene is transcriptionally active in a subpopulation of heart cells, possibly neuronal, which have the potential to synthesize and secrete this neuropeptide. Given the potent coronary vasodilatory and positive chronotropic and inotropic effects of CGRP, the localized synthesis of CGRP in the heart may play a role in modulating cardiovascular function.

Positive inotropic effects of CGRP and isoprenaline: analogies and differences

In guinea-pig isolated left atria, electrically stimulated at 1 Hz, isoprenaline and calcitonin gene-related peptide (CGRP) induced a positive inotropic effect in the same concentration range (0.3-100 nM). The increase in contractile tension induced by both agonists was associated with a reduction in time to peak tension and relaxation time. However CGRP was more active than isoprenaline in reducing the time to peak; this effect was more evident when the bath temperature was reduced from 30 degrees to 24 degrees C. The positive inotropic effects of isoprenaline and CGRP were potentiated by forskolin (30 nM), a direct activator of adenylcyclase; on the other hand, cholera toxin (1 microgram/ml), which irreversibly ribosylates Gs protein, did not modify the effect of CGRP, while antagonizing the concentration-response curve for isoprenaline. It is concluded that the increase in atrial contractile tension produced by isoprenaline and CGRP are linked to the adenylcyclase system in a different manner.

Effects of calcitonin gene-related peptide on cardiac contractility, coronary hemodynamics and myocardial energetics in idiopathic dilated cardiomyopathy

This study was performed to examine the effects of calcitonin gene-related peptide on cardiac function and coronary circulation in patients with heart failure. Synthetic human calcitonin gene-related peptide was infused in the left main coronary artery of 9 patients undergoing cardiac catheterization at different doses corresponding to incremental infusion rates of 15, 50, 150 and 600 pmol.min-1. No hemodynamic change was observed in response to administration of the 2 lowest doses. The 2 highest doses induced an increase in cardiac index and a decrease in systemic arterial pressure. The infusion of 600 pmol.min-1 resulted in a decrease of mean systemic arterial pressure (86.8 +/- 6.5 to 71.8 +/- 4.9 mm Hg; p less than 0.01), and an increase in both cardiac index (2.1 +/- 0.1 to 3.1 +/- 0.17 liters.min-1.m-2; p less than 0.01) and heart rate (87 +/- 3.7 to 101 +/- 6.1 beats.min-1; p less than 0.01). These hemodynamic changes were associated with a significant increase in plasma norepinephrine and epinephrine concentrations. Peak positive first derivative of left ventricular pressure did not change at any infusion rate. Left ventricular end-diastolic pressure decreased at the 2 highest doses associated with a decrease in plasma atrial natriuretic factor concentration (730 +/- 140 to 436 +/- 115 pg.ml-1; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)