Role of calcitonin gene-related peptide and capsaicin-sensitive afferents in central thyrotropin-releasing hormone-induced hepatic hyperemia.

The involvement of capsaicin-sensitive afferent neurons and calcitonin gene-related peptide (CGRP) in the central thyrotropin-releasing hormone (TRH)-induced hepatic hyperemia was investigated in urethane anesthetized rats. Both systemic capsaicin pretreatment and intravenous administration of CGRP receptor antagonist, human CGRP-(8-37), completely abolished the stimulatory effect of hepatic blood flow induced by intracisternal injection of TRH analog (RX-77368; p-Glu-His-(3,3'-dimethyl)-Pro-NH2, 100 ng), assessed by the hydrogen gas clearance method. These data demonstrate the involvement of capsaicin-sensitive afferent neurons and CGRP in the central TRH-induced stimulation of hepatic blood flow.     

Effect of calcitonin gene-related peptide on angiotensin II-induced proliferation of rat vascular smooth muscle cells

The present study was designed to examine the effect of calcitonin gene-related peptide (CGRP) on angiotensin II-induced proliferation of cultured rat vascular smooth muscle cells. Vascular smooth muscle cells were grown from explants of Sprague-Dawley rat aorta. Vascular smooth muscle cells (between passages 5 and 10) were incubated with 0.1% neonatal calf serum for 48 h, and then treated with angiotensin II (100 nM) in the absence or presence of CGRP for 24 h. The viability, DNA synthesis and cell cycle of vascular smooth muscle cells were measured. Western blotting was used to determine the activity of intracellular extracellular regulated kinase (ERK1/2). Angiotensin II significantly decreased the viability and proliferation of vascular smooth muscle cells, decreased the proliferation index, and increased the activity of ERK1/2; the effects of angiotensin II were inhibited by CGRP (1-100 nM) in a concentration-dependent manner. In conclusion, CGRP significantly inhibits angiotensin II-induced proliferation of vascular smooth muscle cells, an effect related to a decrease in the activation of mitogen-activated protein kinase pathway.     

4991W93 inhibits release of calcitonin gene-related peptide in the cat but only at doses with 5HT(1B/1D) receptor agonist activity?

Calcitonin gene-related peptide (CGRP) is a marker for trigeminovascular activation and is released during the headache phase of migraine and cluster headache. CGRP may have a role in migraine through its potent cranial vasodilator effects, or by an action on trigeminal nerve activity, both of which are targeted by 5HT(1B/1D) agonist drugs. CP122,288, a conformationally restricted analogue of sumatriptan that is a potent inhibitor of neurogenic plasma protein extravasation (PPE), was ineffective at inhibiting CGRP release at a single low dose; and is also ineffective as an acute anti-migraine compound. However, it remained unclear as to whether, as a class, the conformationally-restricted triptan analogues could have inhibitory effects on CGRP in higher doses. 4991W93, a conformationally restricted analogue of zolmitriptan, is also a potent inhibitor of PPE at doses without 5HT(1B/1D)-mediated effects, that was developed as an anti-migraine drug, and thus was suitable to test whether higher doses of such conformationally restricted triptan analogues could inhibit trigeminal-evoked CGRP release. The superior sagittal sinus (SSS) was stimulated in 14 anaesthetised cats and external jugular vein blood samples were analysed by radioimmunoassay for CGRP levels before, 1 min after SSS stimulation, and 1 min after SSS stimulation in the presence of 4991W93. Stimulation of the SSS resulted in release of CGRP from the external jugular vein. 4991W93 at a dose of 0.1 and 10 microg/kg, selected for maximal PPE blocking effects in rodents, was ineffective at inhibiting CGRP release, with an SSS stimulation level of 78+/-4 pmol/l compared to a post-4991W93 level of 79+/-3 pmol/l (n=4). In comparison CGRP release was inhibited after a dose of 100 microg/kg 4991W93 from 64+/-6 to 36+/-3 pmol/l (n=5). Given that 4991W93 is inactive clinically at non-vascular doses, it seems clear that the 5HT(1B/1D) agonist effects of the compound are necessary for blockade of CGRP release and thus any anti-migraine action. Taken with the clinical results, these data emphasise the importance of CGRP release in migraine, and suggest that other non-5HT-based pharmacological targets may account for PPE blockade in animal studies.     

Involvement of calcitonin gene-related peptide in the development of tolerance to nitroglycerin in the rat

Previous studies have shown that the depressor effect of nitroglycerin is related to stimulation of endogenous calcitonin gene-related peptide (CGRP) release. In the present study, we explored whether endogenous CGRP is involved in the development of tolerance to nitroglycerin in the rat. Tolerance was induced by treatment with nitroglycerin (10 mg/kg, subcutaneous [s.c.]) three times a day for 8 days and confirmed by a reduction in hypotensive responses to intravenous (i.v.) nitroglycerin. Nitroglycerin (30 or 150 microg/kg, i.v.) significantly decreased blood pressure concomitantly with an increase in plasma concentration of nitric oxide (NO) and CGRP, and these effects of nitroglycerin disappeared after pretreatment with nitroglycerin for 8 days. However, the nitroglycerin-induced depressor effect and elevation of NO and CGRP content were restored, partially or completely, 4 or 8 days after nitroglycerin removal in the tolerant rat. The present study suggests that the development of tolerance to nitroglycerin is related to the decreased release of CGRP in the rat.     

Stimulation of adenylate cyclase by amylin in CHO-K1 cells.

The CHO-K1 cell line responds to the peptide amylin by a rapid elevation of cAMP. The related peptide calcitonin gene-related peptide (CGRP) is 100 times less potent at stimulating adenylate cyclase than is amylin. The actions of amylin at this receptor are concentration dependent and not antagonized by the CGRP antagonist CGRP-(8-37). Although these cells have receptors for calcitonin, amylin is unable to take part in any high affinity interaction with these receptors, as assessed by radioligand binding. The CHO-K1 cell line has receptors for amylin that are distinct from those for calcitonin and CGRP.     

Morphine-induced modulation of calcitonin gene-related peptide levels.

Calcitonin gene-related peptide (CGRP) is a novel calcium-modulatory product of the gene that encodes for calcitonin. Acute administration of morphine decreases levels of CGRP in rat corpus striatum. Tolerance to morphine did not alter the levels of CGRP in any brain region or in the spinal cord of the rat. CGRP did not alter the tolerance to the antinociceptive effects of morphine. Chronic naltrexone increased the levels of CGRP in the hypothalamus. Concurrent chronic administration of naltrexone plus morphine raised the levels of CGRP in the medulla, midbrain, and spinal cord. CGRP enhances naloxone-precipitated withdrawal jumping in mice. In rats, during withdrawal the levels of CGRP were tripled in the corpus striatum and significantly reduced in the hippocampus and hypothalamus. In the corpus striatum, CGRP enhances forskolin-stimulated cyclic adenosine monophosphate (cAMP) accumulation when such accumulation is suppressed (as with the chronic opiate administration), but conversely depresses forskolin-stimulated cAMP accumulation under normal conditions (as with chronic vehicle administration). These data are consistent with the hypothesis that CGRP acts as a modulatory peptide in opiate-sensitive systems and tonic opioid control of CGRP levels exists in brain.     

Calcitonin gene-related Peptide-mediated depressor effect and inhibiting vascular hypertrophy of rutaecarpine in renovascular hypertensive rats

Calcitonin gene-related peptide (CGRP), the predominant neurotransmitter in capsaicin-sensitive sensory nerves, is a potent vasodilator and inhibits proliferation of vascular smooth muscle cells. Previous investigations have demonstrated that the hypotensive effect of rutaecarpine (Rut) is associated to stimulation of CGRP synthesis and release via activation of the vanilloid receptor subtype 1 (VR1) in the phenol-induced hypertensive rat. This study tested whether the depressor effect and inhibiting vascular hypertrophy of Rut is mediated by endogenous CGRP in 2-kidney, 1-clip (2K1C) hypertensive rats. Systolic blood pressure (SBP) was measured by tail-cuff method in conscious. Mesenteric arteries were isolated for examination of morphological changes. The concentration of CGRP in the plasma and the expression of CGRP mRNA in dorsal root ganglia (DRG) were measured. Chronic administration of Rut (10, 20, or 40 mg/kg/day, respectively) for 4 weeks caused a depressor effect and significantly regressed the lumen diameter and decreased the medium thickness of mesenteric arteries in hypertensive rats concomitantly with an increase in the plasma concentration of CGRP and the expression of CGRP mRNA in DRG. In conclusion, chronic administration of Rut can reduce blood pressure and relieve mesenteric artery hypertrophy in the 2K1C hypertensive rats, and the effects of Rut may be related to stimulation of CGRP synthesis and release.     

Involvement of calcitonin gene-related peptide and capsaicin-sensitive afferents in central thyrotropin-releasing hormone-induced hepatic cytoprotection

The involvement of capsaicin-sensitive afferent neurons and calcitonin gene-related peptide (CGRP) in central thyrotropin-releasing hormone (TRH)-induced hepatic cytoprotection was investigated in rats. Both systemic capsaicin pretreatment and intravenous administration of CGRP receptor antagonist, human CGRP-(8-37), completely abolished the protective effect of intracisternal TRH analog (RX-77368; p-Glu-His-(3,3'-dimethyl)-Pro-NH2, 5 ng) against carbon tetrachloride (CCl4)-induced acute liver injury, assessed by serum alanin aminotransferase levels and histological changes. These data demonstrate the involvement of capsaicin-sensitive afferent neurons and CGRP in central TRH-induced hepatic cytoprotection.     

Calcitonin gene-related peptide-induced suppression of atrial natriuretic peptide release through receptors for CGRP1 but not for calcitonin and amylin

Calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide, is found in the central nervous system as well as in the heart. CGRP shows high sequence homology with amylin, salmon calcitonin, and adrenomedullin. This study aimed to investigate the effect of CGRP on atrial hemodynamics and atrial natriuretic peptide (ANP) release by using isolated perfused beating left atria and to identify its receptor subtypes. Rat alpha-CGRP (0.1, 1, 10, or 100 nM) increased atrial contractility and suppressed the release of ANP in a concentration-dependent manner. However, cys-CGRP (1 microM), a CGRP(2) receptor agonist, slightly decreased ANP release without positive inotropism. Human alpha-CGRP (1 nM) showed an effect on ANP release similar to that of rat alpha-CGRP with potent positive inotropism. However, salmon and rat calcitonin (1 microM) caused a slight decrease or no change in ANP release. Pretreatment with a receptor antagonist for CGRP(1) [rat alpha-CGRP-(8-37)] blocked rat alpha-CGRP-induced suppression of ANP release and positive inotropism, whereas the antagonists for salmon or amylin did not. Therefore, we suggest that rat alpha-CGRP causes a suppression of ANP release with positive inotropism through the receptor for CGRP(1) but not that for calcitonin and amylin.     

Rutaecarpine attenuates hypoxia-induced right ventricular remodeling in rats

Rutaecarpine has been shown to exhibit wide pharmacological effects in the cardiovascular system via stimulation of calcitonin gene-related peptide (CGRP) release. In the present study, the effect of rutaecarpine on hypoxia-induced right ventricular (RV) remodeling and the underlying mechanisms were evaluated. RV remodeling was induced by hypoxia (10 % O₂, 3 weeks) in rats. Rats were treated with rutaecarpine (20 or 40 mg/kg) by intragastric administration. Proliferation of cardiac fibroblasts was induced by TGF-β1 (5 ng/mL) and determined by MTS and EdU incorporation method. Cardiac fibroblasts were treated with exogenous CGRP (10 or 100 nM). The concentrations of CGRP and TGF-β1 in plasma were measured by ELISA. The expression of eIF3a, p27, α-SMA, collagen-I/III, ANP, and BNP were measured by real-time PCR or western blot. Hypoxia induced an increase of right ventricle systolic pressure (RVSP), ration of RV/LV+S, and RV/tibial length in rats, while cardiac hypertrophy, apoptosis, and fibrosis were detected. The expression of ANP, BNP, α-SMA, collagen-I, collagen-III, eIF3a, and TGF-β1 was up-regulated, and the expression of p27 was down-regulated in the right ventricle of hypoxia-treated rats. The plasma concentration of CGRP was decreased and TGF-β1 was increased in hypoxia-treated rats. All of these effects induced by hypoxia were attenuated by rutaecarpine in a dose-dependent manner. In cultured cardiac fibroblasts, TGF-β1 significantly promoted the proliferation and up-regulated the expression of α-SMA and collagen-I/III, while the expression of eIF3a was up-regulated and the expression of p27 was down-regulated. The effects of TGF-β1 were attenuated by CGRP. CGRP_8–37, a selective CGRP receptor antagonist, abolished the effects of CGRP. Rutaecarpine attenuates hypoxia-induced RV remodeling via stimulation of CGRP release, and the effects of rutaecarpine involve the eIF3a/p27 pathway.     

Involvement of multiple receptors in the biological effects of calcitonin gene-related peptide and amylin in rat and guinea-pig preparations.

1. The activity of rat alpha and beta calcitonin gene-related peptide (CGRP) as compared to the structurally related peptide, rat amylin, has been investigated in the guinea-pig isolated left atrium (electrically driven), in mucosa-free strips from the base of the guinea-pig urinary bladder and in the rat isolated vas deferens (pars prostatica). The antagonist activity of the C-terminal fragment of human alpha CGRP, alpha CGRP(8-37), was also investigated. 2. In the guinea-pig isolated left atrium the three peptides produced a concentration-related positive inotropic effect, amylin being about 16 and 31 times less potent than alpha or beta CGRP, respectively. Human alpha CGRP(8-37) produced a rightward displacement of the log concentration-response curve to the three agonists tested, without depression of maximal response attainable. Apparent pKB values calculated on the basis of the displacement produced by 1 microM human alpha CGRP(8-37) indicated an agonist-independent affinity of the antagonist (6.66 +/- 0.11 for alpha CGRP, 6.42 +/- 0.17 for beta CGRP and 6.95 +/- 0.11 for amylin). 3. In the guinea-pig isolated urinary bladder, alpha or beta CGRP or amylin produce a concentration-related inhibition of twitch contractions evoked by train electrical field stimulation (10 Hz frequency, 0.25 ms duration at 100 V for 0.5 s every 60 s). Amylin was about 100 times less potent than alpha or beta CGRP. Human alpha CGRP(8-37) (3 microM) did not significantly affect the inhibitory action of the three agonists tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitric oxide mediates rat mucosal vasodilatation induced by intragastric capsaicin.

The role of endogenous nitric oxide (NO) in the gastric mucosal vasodilatation induced by acute intragastric perfusion with capsaicin or close-arterial infusion of rat alpha-calcitonin gene-related peptide (CGRP) was evaluated in the pentobarbitone-anaesthetised rat using laser Doppler flowmetry (LDF). The mucosal vasodilatation induced by intraluminal capsaicin (160 microM) was dose dependently reduced by the inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (L-NAME; 1-5 mg kg-1 i.v.), effects reversed by concurrent administration of L-arginine (100 mg kg-1 i.v.). L-NAME (2 mg kg-1) induced a small reduction in the mucosal vasodilatation induced by close-arterial infusion of rat alpha-CGRP (50 pmol kg-1 min-1). These findings indicate a role of NO in the gastric vasodilatation induced by stimulation of sensory neurones with intragastric capsaicin.     

Action of calcitonin gene-related peptide on rat aortic smooth muscle

The effects of rat calcitonin gene-related peptide (CGRP) on superfused rat aortic smooth muscle cells in cell culture were investigated. Exposure of the cells for 10 min to CGRP (10(-7) M), with or without pretreatment with pertussis toxin, stimulated the release of cyclic AMP but not of prostacyclin, as judged by radioimmunoassay of its stable metabolite, 6-keto-PGF1 alpha. Pretreatment of the cells with pertussis toxin did not alter the response to CGRP. The direct action of CGRP on smooth muscle cells and on the CGRP-induced formation of cyclic AMP did not appear to depend on the production of prostacyclin in these vascular smooth muscle cells.     

Protective effects of rutaecarpine in cardiac anaphylactic injury is mediated by CGRP

Previous investigations have indicated that rutaecarpine activates the vanilloid receptor to evoke calcitonin gene-related peptide (CGRP) release. CGRP has been shown to alleviate cardiac anaphylactic injury. In the present study, the effect of rutaecarpine on cardiac anaphylaxis was examined. Challenge of presensitized guinea-pig hearts with a specific antigen caused marked decreases in coronary flow (CF), left ventricular pressure (LVP) and its derivatives (+/- dp/dt(max)), an increase in heart rate, and prolongation of the P-R interval. Rutaecarpine (0.3 or 1 microM) markedly increased the content of calcitonin gene-related peptide (CGRP) in the coronary effluent and decreased the content of tumor necrosis factor-alpha (TNF-alpha) in myocardial tissues concomitantly with a significant improvement of cardiac function and alleviation of the extension of the P-R interval. Rutaecarpine at the concentration of 1 microM also inhibited the sinus tachycardia. The protective effects of rutaecarpine on cardiac anaphylaxis were abolished by CGRP (8-37), a selective CGRP receptor antagonist. These results suggest that the protective effects of rutaecarpine on cardiac anaphylactic injury are related to inhibition of TNF-alpha production by stimulation of CGRP release.     

Cardiovascular effects of human and rat CGRP compared in the rat and other species

In the anaesthetised rat, human and rat CGRP (calcitonin gene-related peptide) which differ by 4 out of 37 amino acids, when given intravenously, lowered blood pressure and increased heart rate. The effects of human CGRP were unaltered by either propranolol or by mepyramine plus cimetidine. In the rat isolated perfused heart the peptides decreased coronary perfusion pressure and evoked a tachycardia. The latter effect was not seen in the rabbit isolated heart, although human CGRP increased coronary flow. The two peptides were equipotent at increasing the rate and force of contraction in the rat isolated right atrium, effects unaltered by propranolol. In the guinea-pig isolated atrium, rat CGRP was 10 times as potent as a chronotropic agent than as an inotrope, unlike human CGRP which was equipotent. In conclusion, human and rat CGRP probably acted directly on the cardiovascular system to produce their qualitatively similar effects.     

降钙素基因相关肽预处置对阿霉素所致离体大鼠心脏损伤的保护作用

在离体灌流大鼠心脏研究了降素基因相关肽（CGRP）预处理对阿霉素所致心肌损伤的保护作用。阿霉素（100和200μmol/L）导致冠脉流量减少，心脏功能降低和丙二醛（MDA）含量的升高。CGRP（5nmol/L）灌流预处置5分钟能增加冠脉流量，改善心脏功能及抑制MDA的升高。这些结果提示：CGRP预处置对阿霉素所致的心脏损伤具有保护作用，其保护作用可能与抑制脂质过氧化有关。     

Lafutidine changes levels of somatostatin, calcitonin gene-related peptide, and secretin in human plasma

We examined the effects of the histamine H2-receptor antagonist, lafutidine, on the levels of gastrointestinal peptides (somatostatin, calcitonin gene-related peptide (CGRP), gastrin, secretin, and motilin) in plasma from healthy subjects. After a single oral administration of lafutidine (10 mg), the plasma lafutidine level (186 +/- 13.4ng/ml) was highest in the 60-min sample after administration and then the plasma level fell. Lafutidine caused significant increase in plasma somatostatin levels at 20 to 120 min and in CGRP levels at 40 to 120 min, compared with a placebo group. The physiological release of plasma secretin was reduced by administration of lafutidine, but the medicine did not alter the level of gastrin or motilin. These results suggest that the pharmacological effects of lafutidine on regulation of gastrointestinal functions closely relate to changes of somatostatin-, CGRP- and secretin-immunoreactive substance levels in human plasma.     

Regional haemodynamic effects of depressor neuropeptides in conscious, unrestrained, Long Evans and Brattleboro rats.

1. The regional haemodynamic effects of i.v. bolus doses of atrial natriuretic peptide (ANP, 1 and 10 nmol), calcitonin gene-related peptide (CGRP, 0.05 and 0.5 nmol) and corticotropin-releasing factor (CRF, 1 and 5 nmol) were assessed in conscious Long Evans and Brattleboro rats chronically instrumented with miniaturized, pulsed Doppler probes. 2. The low dose of ANP was without effect on mean arterial pressure (MAP), but caused tachycardia and hindquarters vasodilatation with vasoconstriction in renal and mesenteric beds in Long Evans rats. With the high doses of ANP these effects were more pronounced and MAP fell. In Brattleboro rats there was a primary renal vasodilatation. 3. The low dose of CGRP caused a slight fall in MAP in Long Evans rats, tachycardia and a renal vasodilatation. The high dose of CGRP caused marked hypotension, tachycardia and renal, mesenteric and hindquarters vasodilatation in both strains of rat. However, only in Long Evans rats were there secondary renal and mesenteric vasoconstrictions. 4. The low dose of CRF caused falls in MAP in both strains of rat, accompanied by renal and, particularly, mesenteric vasodilatation. Administration of the high dose of CRF caused profound, prolonged hypotension, tachycardia and mesenteric vasodilatation. There was also (late onset) hindquarters vasodilatation accompanying renal vasoconstriction that followed the initial vasodilatation in this vascular bed. 5. These results indicate that appropriate doses of particular peptides may be capable of promoting flow through individual peripheral vascular beds.     

Sensitization versus tolerance to haloperidol-induced catalepsy: multiple determinants

The effects of dose, administration frequency, and behavioral testing conditions on the development of tolerance versus sensitization to haloperidol-induced catalepsy were tested in rats. Animals received daily or weekly injections of haloperidol (0.05-5.00 mg/kg SC) for up to 22 days. Catalepsy assessments were made either once or repeatedly using two tests: the horizontal bar and the inclined screen. Tolerance was found only in animals treated daily with haloperidol (1.5 mg/kg) and tested repeatedly on the horizontal bar. In contrast, sensitization was observed with various haloperidol doses, daily or weekly administration schedules (for most doses), either horizontal bar or inclined screen catalepsy tests, and repeated or single testing. Sensitization developed most strongly following weekly drug administration and repeated testing on the horizontal bar. No single experimental variable produced a definitive pattern of change in catalepsy over time. Dose, drug administration schedule, and behavioral test conditions all influenced the evolution of catalepsy during chronic haloperidol treatment.     

The protective effects of rutaecarpine on gastric mucosa injury in rats

Previous investigations have shown that calcitonin gene-related peptide (CGRP) protects gastric mucosa against injury induced by acetylsalicylic acid (ASA) and that rutaecarpine activates vanilloid receptors to evoke CGRP release. In the present study, we examined the protective effects of rutaecarpine on gastric mucosa injury, and explored whether the protective effects of rutaecarpine are related to stimulation of endogenous CGRP release via activating vanilloid receptors in rats. In an ASA-induced ulceration model, gastric mucosal ulcer index, pH value of gastric juice and plasma concentrations of CGRP were determined. ASA significantly increased the gastric mucosal ulcer index and the back-diffusion of H+ through the mucosa. Rutaecarpine at the doses of 100 or 300 microg/kg (i.v.), and 300 or 600 microg/kg (intragastric, i.g.) reduced the ulcer index and back-diffusion of H+, which was abolished by pretreatment with capsaicin (50 mg/kg, s.c.) or capsazepine (3 mg/kg, i.v.), a competitive vanilloid receptor antagonist. Rutaecarpine significantly increased the plasma concentration of CGRP, which was also abolished by capsazepine. In a stress-induced ulceration model, rutaecarpine reduced gastric mucosal damages, which was abolished by capsazepine (5 mg/kg, i.p.). These results suggest that rutaecarpine protects the gastric mucosa against injury induced by ASA and stress, and that the gastroprotective effect of rutaecarpine is related to a stimulation of endogenous CGRP release via activation of the vanilloid receptor.