Cardiovascular effects of calcitonin gene-related peptides I and II in man

Interrelationships between calcitonin gene-related peptide and sympathoadrenomedullary system: effects of administration of epinephrine and norepinephrine in healthy man

To investigate the influence of the sympathoadrenomedullary system on the modulation of the circulating levels of calcitonin gene-related peptide (CGRP), the effects of epinephrine (E) and norepinephrine (NE) were studied in 8 normal subjects (4 females and 4 males). The mean basal levels of CGRP in normal subjects were 10.2 +/- 1 pmol/l. After the infusion of E (20 ng/kg per min for 30 min), a significant rise (P < 0.005) in plasma CGRP levels was observed with the expected increases in systolic blood pressure (BP), heart rate (HR) and plasma renin activity (PRA), and decrease in diastolic BP, whereas plasma aldosterone (PA) levels did not significantly change. The infusion of NE (40 ng/kg per min for 30 min) induced an increase in systolic and diastolic BPs, whereas it failed to modify CGRP, HR, PA and PRA. Our data demonstrate that the sympathoadrenomedullary system may modulate CGRP release in man perhaps via the beta-adrenergic pathway. It is likely that the modifications of plasma CGRP levels may be part of the acute vasal response to E.

Carotid blood flow distribution, haemodynamics and inotropic responses following calcitonin gene-related peptide in the pig

The sensory neuropeptide, calcitonin gene-related peptide (alpha-CGRP), has been implicated in the pathogenesis of migraine headache. The present study aimed to evaluate the effects of intracarotid infusions of human alpha-CGRP (10, 30 and 100 pmol/kg.min; n = 8), as compared to that of saline (4 times; n = 8) on haemodynamics and blood flow distribution within the carotid circulation of the anaesthetized pig, using the radioactive microsphere method. Furthermore, the effects of antimigraine drugs, dihydroergotamine (100 micrograms/kg i.v.; n = 4) or sumatriptan (300 micrograms/kg i.v.; n = 4), on these parameters were studied in the presence of the infusion of the highest concentration of human alpha-CGRP. Additionally, putative positive inotropic responses to human alpha-CGRP (10(-9)-10(-7) M) were investigated in porcine isolated atrial and ventricular trabeculae. Human alpha-CGRP increased carotid artery blood flow and conductance dose-dependently, together with an enhancement in vascular pulsations. These effects were associated with a fall in systemic blood pressure with concomitant increases in heart rate and cardiac output. The increase in carotid blood flow was reflected by an increase in total capillary blood flow, predominantly to extracerebral tissues including the dura, whereas blood flow through arteriovenous anastomoses remained stable. Both dihydroergotamine and sumatriptan reduced carotid blood flow and its capillary fraction without affecting systemic vascular conductance. In tissues, these drugs reversed blood flow increases due to human alpha-CGRP in most extracerebral tissues, but failed to reduce dural blood flow. In porcine isolated atrial and ventricular trabeculae, noradrenaline (10(-8)-10(-5) M) increased force of contraction in a concentration-dependent manner. In contrast, human alpha-CGRP (10(-9)-10(-7) M) failed to increase force of contraction in atrial trabeculae (n = 6) and exerted only a moderate concentration-dependent positive inotropic effect in ventricular trabeculae (approximately 25% of the response to 10(-5) M noradrenaline, n = 10). These data indicate that human alpha-CGRP caused arteriolar dilatation together with a fall in blood pressure in the pig. The tachycardia may be reflex-mediated, but the peptide also exerts a moderate positive inotropic action on ventricular trabeculae. The fall in systemic arterial blood pressure and the marked increase in capillary blood flow most likely prevented the opening of arteriovenous anastomoses. Furthermore, the antimigraine drugs, dihydroergotamine and sumatriptan, were able to reverse blood flow changes induced by human alpha-CGRP in the porcine carotid circulation.

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

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

Different pharmacological responses of atrium and ventricle: studies with human cardiac tissue

It has been recently reported that 5-hydroxytryptamine (5-HT) increases force of contraction in atrial tissue but not in ventricular tissue. In the present study with trabeculae obtained from non-diseased human hearts, we investigated whether this difference in the contractile responses is specific for 5-HT or is also observed for other substances: calcitonin gene-related peptide (CGRP), angiotensin II, adenosine, somatostatin and acetylcholine. CGRP (10(-9) to 10(-7) M) and angiotensin II (10(-9) to 10(-5) M) caused concentration-dependent increases in force of contraction in atrial trabeculae (up to 36 +/- 8% and 42 +/- 8% of the response to 10(-5) M noradrenaline, respectively). Similar to 5-HT, no effects were observed with CGRP and angiotensin II in ventricular trabeculae. Adenosine (10(-8) to 10(-5) M) and somatostatin (10(-8) to 10(-6) M) caused concentration-dependent negative inotropic effects on baseline atrial contractility (-54 +/- 17% and -51 +/- 25%, respectively), but no response was found on baseline ventricular contractility. Adenosine, but not somatostatin, reduced force of contraction after pre-stimulation with 10(-5) M noradrenaline in atrial tissue and, to a lesser extent, in ventricular tissue. Acetylcholine exhibited a biphasic concentration-response curve in the atrial tissue, consisting of an initial negative inotropic response (10(-9) to 10(-7) M, from 120 +/- 41 mg at baseline to 48 +/- 16 mg at 10(-7) M), followed by a positive inotropic response (10(-6) to 10(-3) M, from 48 +/- 16 mg at 10(-7) M to 77 +/- 15 mg).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

In vitro expression of calcitonin gene-related peptide in human endothelial cells transfected with plasmid and retroviral vectors

Introduction of cDNA encoding human alpha-calcitonin gene-related peptide (CGRP), a potent vasodilator, into cultured human umbilical vein endothelial cells (HUVEC) was undertaken by using plasmids and retroviral vectors. In order to improve expression, modification of context coding sequence for the initiation of CGRP translation and deletion of nontranslated regions of CGRP cDNA in the transfection vectors were tested. Stable transfer of neo in the HUVEC was achieved with both plasmid and retroviral vectors. Integration rates obtained by using retrovirus (approximately 1%), where higher than those achieved with plasmid-mediated transfection (< 1/1000). CGRP expressed in the transfected HUVEC was secreted into culture medium when a leading sequence was included in the expression vectors. CGRP was detected by enzyme-linked immunosorbent assay (ELISA) in the supernatants of both transiently transfected and stably transfected/infected HUVEC. Higher levels of expression were achieved by using plasmid (giving a maximum CGRP concentration of 6.5 +/- 0.5 pM in the supernatant) than retroviruses. Lipofectin-mediated transfer of CGRP cDNA also resulted in transient expression of CGRP in the HUVEC.

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.

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

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

Effects of calcitonin gene-related peptide on the rabbit electroretinogram

In order to better understand the role of Calcitonin gene-related peptide (CGRP) in mammalian retina, the dose related effects of human CGRP (hCGRP) on rabbit electroretinogram (ERG) were examined in the present study. CGRP was administered intraocularly in doses of 0.1, 1.0 and 10.0 micrograms. ERG A- and B-wave as well as oscillatory potentials (P1, P2, P3 and P4) were recorded. The highest dose of CGRP (10.0 micrograms) significantly increased the amplitudes of the A-wave and OP components (P1, P2, P3 and P4) produced by relatively high stimulus intensity. The same dose of the peptide also enhanced B-wave amplitude at all intensities studied. The effects of the intermediate dose of CGRP (1.0 microgram) on the B-wave amplitudes were dependent on stimulus intensities. B-wave amplitudes at high stimulus intensities were not affected by 1.0 microgram of CGRP but were significantly increased with relatively lower stimulus intensities. The amplitudes of P3, one of OP components, were significantly increased. However, amplitudes of A-wave and other OP components (P1, P2 and P4) were not affected by 1.0 microgram CGRP. The lowest dose of the peptide (0.1 microgram) did not affect any amplitudes of ERG components. Implicit times of A-wave, B-wave and OP components were not significantly affected by the different doses of CGRP. Taken together, these results indicate that CGRP may play a functional role in modulating retinal responses to photic stimulation.

Possible physiologic role of calcitonin gene-related peptide in the human uterine artery

OBJECTIVE

The purpose of our study was to determine the potential physiologic role of calcitonin gene-related peptide as an endogenous vasodilator of human uterine arteries during pregnancy.

STUDY DESIGN

Isolated, suffused uterine arteries from pregnant patients (n = 9) and nonpregnant patients (n = 19) were used in the study.

RESULTS

Calcitonin gene-related peptide (1 nmol/L to 0.1 mumol/L) produced a concentration-dependent relaxation of norepinephrine (1 mumol/L)-induced contractions. The values of calcitonin gene-related peptide that inhibited norepinephrine-induced contractions by 50% were 0.9 +/- 0.7 nmol/L (n = 8) and 6.5 +/- 1.5 nmol/L (n = 12) in pregnant and nonpregnant arteries, respectively. The calcitonin gene-related peptide-induced relaxation was not affected by propranolol (1 mumol/L), indomethacin (5 mumol/L), methylene blue (10 mumol/L), or by the removal of the endothelium. The relaxant effect of calcitonin gene-related peptide was inhibited by human calcitonin gene-related peptide(8-37). The endogenous levels of calcitonin gene-related peptide were 110.2 +/- 13.5 pmol/L/gm wet weight in pregnant arteries and 14.8 +/- 3.2 pmol/L/gm wet weight in nonpregnant arteries.

CONCLUSIONS

These results demonstrate that the vasodilatory effect of calcitonin gene-related peptide is mediated by calcitonin gene-related peptide1 receptors and does not involve beta-adrenoceptors, vasodilator prostanoids, increased levels of guanosine 3',5'-cyclic monophosphate, or endothelium-derived relaxing factor. The findings that calcitonin gene-related peptide acts as a potent dilator and that pregnancy increases both the sensitivity to calcitonin gene-related peptide and the endogenous levels of calcitonin gene-related peptide support the view that calcitonin gene-related peptide has a physiologic role in dilating the uterine vasculature, especially during pregnancy.

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)

Comparison of a calcitonin gene-related peptide receptor in a human neuroblastoma cell line (SK-N-MC) and a calcitonin receptor in a human breast carcinoma cell line (T47D)

A specific CGRP-binding protein of M(r) 60,000 has been identified in the human neuroblastoma cell line SK-N-MC. After N-deglycosylation a M(r) of 48,000 was found. The M(r) were indistinguishable from those determined in the human cerebellum. Receptor binding of CGRP is coupled to cyclic AMP formation. The latter is antagonized by hCGRP-I8-37. CT and DAPamide interact only minimally with the CGRP receptor, whereas CGRP and DAPamide are full agonists in T47D cells. The CT receptor on human breast cancer cell line T47D is clearly different from the human CGRP receptor.

Structural studies on the [Bu(t)-Cys18](19-37)-fragment of human beta-calcitonin-gene-related peptide

High-field n.m.r. studies were undertaken upon a peptide fragment of the C-terminal region of human beta-calcitonin-gene-related peptide (beta-hCGRP). Studies on the antigenic [Bu(t)-Cys18]beta-hCGRP-(19-37)-fragment revealed that several elements of secondary structure were present when the peptide was dissolved in [2H6]dimethyl sulphoxide. In particular an unspecified turn in the region of Ser19-Gly20 and a type I beta-turn in the region of Asn31-Val32-Gly33 were identified. Through-space connections between the terminal Phe37 amide group and the beta-protons of Thr50 suggest that the peptide may be folded into a loop-type conformation. These structural elements appear to overlap with the epitopes of a number of monoclonal antibodies and provide a molecular basis for understanding the role of the terminal Phe37 amide residue in the immune recognition of beta-hCGRP.

Distinct hemodynamic and gastric effects of human CGRP I and II in man

The human calcitonin gene-related peptides I and II (or alpha and beta) (CGRP I and II) are encoded by two different genes, but they have 34 of the 37 amino acid residues in common. Human CGRP I more potently stimulated blood flow through the skin and carotid artery (p less than 0.01), and the heart rate (p less than 0.05), and plasma renin activity and aldosterone secretion than human CGRP II (p less than 0.02). Inhibition of pentagastrin-stimulated gastric acid output, on the other hand, was only obtained with CGRP II. The separate effects of human CGRP I and II on the cardiovascular and gastric systems are presumably mediated by different receptors or receptor pathways recognized by the two closely related neuropeptides.

Splanchnic and cerebral vasodilatory effects of calcitonin gene-related peptide I in humans

The ability of synthetic human calcitonin gene-related peptide (CGRP I) to act as an arterial vasodilator was tested in healthy men by measuring arterial blood flow parameters in carotid, superior mesenteric, celiac, and femoral vessels. Calculated volume flow was significantly increased (140 +/- 21% of basal) in the SMA with a 2-ng/kg/min infusion of CGRP. Carotid artery volume flow increased dose dependently (96 +/- 6%, 122 +/- 15%, 135 +/- 15% of basal, respectively, with 2, 4, or 8 ng/kg/min). With steady-state infusion, carotid and superior mesenteric arterial flow parameters remained significantly elevated for 30 minutes after cessation of peptide administration. Blood pressure was unchanged. Pulse increased dose dependently. Arterial diameters were unchanged, implying activity at the arteriolar level.

Characterization and photoaffinity labeling of a calcitonin gene-related peptide receptor solubilized from human cerebellum

Calcitonin gene-related peptide (CGRP) receptors were solubilized from human (h) cerebellum with use of the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS). Scatchard analysis of equilibrium binding data indicated that the soluble extract contained a single class of CGRP binding sites with apparent dissociation constants of 50 pM for the intact 125I-hCGRP-I(1-37) and 160 pM for the antagonist 125I-hCGRP-I(8-37). Unlabeled hCGRP-I and -II and hCGRP-I(8-37) displaced 125I-hCGRP-I from solubilized CGRP receptors with similar potencies (ID50 = 70-150 pM). Human CGRP-I(15-37), -(21-37), and -(28-37) were less potent (ID50 greater than or equal to 70 nM), suggesting that amino acid residues 8-14 may be important for maintaining high binding affinity. A novel photoreactive analogue of hCGRP-I, 125I-[C gamma-(4-azidoanilino)Asp3] hCGRP-I, was prepared by carbodiimide coupling of 4-azidoaniline to 125I-hCGRP-I. Photoaffinity labeling of soluble CGRP receptors with the photoreactive analogue and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed three specifically labeled binding proteins with apparent molecular weights (Mr) of 60,000, 54,000, and 17,000. Cross-linking of 125I-hCGRP-I and -II and 125I-hCGRP-I(8-37) to soluble CGRP binding sites using disuccinimidyl suberate revealed three specifically labeled binding proteins with the same Mr. The C-terminal fragment 125I-hCGRP-I(8-37), unlike the intact peptide, was, furthermore, cross-linked specifically to a 95,000 Mr protein. The CGRP receptor is N-glycosylated. Treatment with endoglycosidase F/N-glycosidase F converted the 60,000 and 54,000 to 46,000 and 41,000 Mr components.(ABSTRACT TRUNCATED AT 250 WORDS)

Plethysmographic evaluation of the vascular effects of human calcitonin gene-related peptide in man

Calcitonin gene-related peptide (CGRP) is a neuropeptide with potent cardiovascular effects that include positive inotropic and chronotropic actions systemic vasodilation, and hypotension in animals and in man. The mechanism of action of CGRP is still, however, not clear, and in particular it is not known whether vasodilation by CGRP occurs by changes in cutaneous or in muscular blood flow, or both. The aim of the study was, therefore, to evaluate the cutaneous and muscular blood flow, at rest and after ischemic test, induced by an IV bolus 25 micrograms human CGRP infusion in 5 healthy normotensive volunteers, using a strain gauge plethysmographic procedure with venous occlusion. Human CGRP provoked a transient but significant decrease in systolic and diastolic blood pressure, associated with tachycardia, marked flushing, a significant increase in plasma noradrenaline, adrenaline, and cyclic AMP levels, and a slight, but significant, decrease in serum total calcium. Moreover, a significant increase in the carpal cutaneous blood flow at rest was observed, with no significant change in the lower extremity muscular blood flow at rest and after ischemic test. Finally human CGRP produced a significant increase in the venous partial O2 pressure and in the hematocrit and a significant decrease in the venous partial CO2 pressure. The results of the present study confirm the acute cardiovascular and metabolic effects of CGRP. In fact, hypotension, tachycardia, flushing, and the increased cutaneous blood flow indicate a systemic vasodilation by the neuropeptide, with a secondary sympathetic response, as documented by the augmented catecholamine and cyclic AMP plasma levels.

Effects of prolonged infusion of human alpha calcitonin gene-related peptide on hemodynamics, renal blood flow and hormone levels in congestive heart failure

We have previously demonstrated that short-term infusion of calcitonin gene-related peptide (CGRP) has beneficial effects in congestive heart failure. The effects of prolonged infusion of CGRP on hemodynamic functions, plasma hormones and renal blood flow were studied in 9 patients with congestive heart failure (New York Heart Association class III or IV, ejection fraction less than 35%). Hemodynamic variables were measured at 30-minute intervals for 8 hours during CGRP infusion (8 ng/kg/min) and for 2 hours after discontinuation. CGRP caused a decrease in right atrial (28%, p less than 0.05), pulmonary artery (22%, p less than 0.02), pulmonary artery wedge (37%, p less than 0.001) and systemic arterial (18%, p less than 0.05) pressures. Systemic vascular resistance decreased more than pulmonary vascular resistance. Cardiac output (72%, p less than 0.001) and stroke volume (60%, p less than 0.02) increased. Heart rate did not change. There was no evidence of tolerance throughout the infusion. The hemodynamic effects were lost within 30 minutes of stopping CGRP. Renal blood flow (34%, p less than 0.01) and glomerular filtration rate (43%, p less than 0.01) increased. Atrial natriuretic peptide decreased (p less than 0.05), while plasma cortisol (p less than 0.02) increased. Plasma epinephrine, norepinephrine, renin activity, aldosterone and growth hormone were unchanged. It is concluded that in patients with severe congestive heart failure, CGRP has sustained beneficial effects on hemodynamic functions and has no adverse effects on hormones. Unlike many other vasodilators, CGRP also increases renal blood flow and glomerular filtration.

Calcitonin gene-related peptide and human epicardial coronary arteries: presence, release and vasodilator effects

1. In the present study, the levels of calcitonin gene-related peptide (CGRP)-like immunoreactivity (-LI) in human cardiopulmonary tissue were determined in combination with studies on CGRP-LI release from the left anterior descending coronary artery (LAD) and functional effects of CGRP on coronary arterial tone. 2. The highest levels of CGRP-LI were found in the LAD followed in declining order by the bronchus, right atrium, pulmonary artery, lung and left ventricle. 3. Exposure to capsaicin evoked a clear-cut increase in CGRP-LI outflow, suggesting release from isolated large specimen of the LAD. This release was Ca2(+)-dependent and was markedly attenuated by incubation with the mitochondrial Ca2(+)-inhibitor, ruthenium red. Exposure to potassium also released CGRP-LI in a Ca2(+)-dependent fashion from the LAD. 4. In functional experiments on human epicardial coronary arteries with an inner diameter of 0.4 to 0.8 mm, human CGRP alpha and beta relaxed the potassium-precontracted arteries equipotently. Substance P (SP) also relaxed these precontracted arteries but the relaxation could be prevented by incubation with methylene blue, an inhibitor of endothelium derived relaxing factor (EDRF)-mechanisms, which did not influence the effect of CGRP. 5. Capsaicin evoked a ruthenium red-sensitive relaxation of the potassium-precontracted arteries. However, ruthenium red did not affect the relaxations induced by CGRP or SP. Furthermore, the capsaicin effect was not influenced by methylene blue. 6. It is concluded that CGRP-LI is present in human cardiopulmonary tissue and can be released upon exposure to high concentrations of capsaicin as well as potassium. CGRP causes relaxation of arteries independently of EDRF activation and closely resembles the vasodilator effects of capsaicin. This supports the view that the coronary vasodilatation observed upon sensory nerve activation is mediated by CGRP. Ruthenium red inhibits capsaicin-induced CGRP-LI release and functional effects and may thus serve as an experimental tool in evaluating the function of capsaicin-evoked stimulation of peripheral nerve terminals.

The role of neuropeptides in cardiovascular regulation

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

Cardiovascular and hormonal effects of calcitonin gene-related peptide in congestive heart failure

The effects of infusing human alpha-calcitonin gene-related peptide were studied in eight patients with congestive heart failure, five normal rabbits and five rabbits with adriamycin-induced cardiomyopathy. In patients with heart failure, calcitonin gene-related peptide caused a dose-dependent increase in cardiac output and decrease in pulmonary and systemic vascular resistance and pulmonary artery pressure. The systemic blood pressure and right atrial and pulmonary wedge pressures decreased only at the highest infusion rate (16 ng/kg per min). Heart rate remained unchanged. Plasma epinephrine increased (p less than 0.05), whereas aldosterone, atrial natriuretic peptide and prolactin concentrations decreased (p less than 0.05). Plasma norepinephrine, renin activity, cortisol and growth hormone concentrations remained unchanged. In both groups of rabbits, the drug decreased blood pressure and increased cardiac output and heart rate. There was a significant increase in renal blood flow (p less than 0.05). The peptide did not affect the contraction amplitude of human and rabbit ventricular myocytes. These findings suggest that calcitonin gene-related peptide is a vasodilator in the rabbit and humans with little direct effect on ventricular myocardium. This peptide may be useful in some forms of heart failure.

Calcium metabolism and depressed contractility in isolated human and porcine heart muscle

Contractility is often depressed in isolated heart muscle. To analyze this phenomenon, we measured the derivative of left ventricular pressure (dP/dt) in intact and in isolated, blood perfused pig hearts, and peak force (F) or stress (F/mm2) in ventricular trabeculae of man and pig. When the heart was in the steady state at a priming frequency of 2 Hz an extrasystolic interval of 0.3 s was interposed, followed by four postextrasystolic intervals of 0.8 s. In the case of isolated trabeculae the priming frequency was 0.2 Hz, the extra interval 0.4 s, and the post-extrasystolic intervals were 5 s. The exponential decay of potentiation is characterized by the constant D: a low value of D indicates a rapid decay of potentiation. DP/dt was about 1000 mm Hg/s in the intact hearts, but within 1 h after isolation dP/dt decreased to about 700 mm Hg/s, and this was associated with a decrease in D from 0.63 to 0.40. Developed stress in the isolated trabeculae was about 2 mN/mm2 and D was about 0.20 under standard, in vitro conditions (a.o. 1.5 mM Ca2+. 0.2 Hz stimulus frequency). This stress is only 10% of the calculated stress in the intact heart. An increase of priming frequency, or of [Ca2+], or addition of 30 nM isoproterenol to the perfusate caused a marked increase in F and D. Properties of human and porcine trabeculae were quantitatively similar. The strong correlation between dP/dt, or F, and D suggests a causal relationship. This is consistent with the current model of e-c coupling in heart muscle, in which the activity of the Ca2+ pump of the sarcoplasmic reticulum determines the decay of potentiation and the amount of releasable Ca2+ in the reticulum determines force of contraction. Since isoproterenol stimulates the Ca2+ pump in the reticulum, the increase in D and F induced by this drug is consistent with the model. We conclude, that the decreased dP/dt, F, and D in isolated preparations was due to impaired sarcoplasmic reticulum function. The role of this phenomenon in the stunned heart syndrome, species differences and possible causes are discussed.

Calcitonin gene-related peptide increases coronary flow and decreases coronary resistance

Calcitonin gene-related peptide (CGRP) is a potent vasodilator, but its effects on in situ ventricular function are unknown. We studied effects of intracoronary CGRP (100, 200, and 600 pmole/min, for 10 min) in 21 open-chest chloralose-anesthetized dogs. Systemic, pulmonary, left ventricular (LVP), central venous, and pulmonary capillary wedge pressures were continuously monitored. Left ventricular wall thickness (WT) and circumflex coronary blood flow were also measured. CGRP was infused into the proximal circumflex artery. During CGRP infusion there were no changes in heart rate, cardiac index, pulmonary artery pressure, or systemic vascular resistance, no percentage change in ventricular WT, and no changes in dWT/dt, peak dP/dt, or the slope of end-systolic points on WT/LVP loops. But there were significant changes in coronary flow (CQ), coronary resistance (CRES) and mean arterial blood pressure (MAP) from control (C)* (P less than 0.05). (table; see text) CGRP is a potent coronary artery vasodilator causing notable dose-dependent decreases in coronary resistance and a rise in myocardial flow, despite a decreased MAP (all P less than 0.05). CGRP does not affect ventricular contractility in vivo.

The effect of calcitonin gene-related peptide (CGRP) on human forearm blood flow

The effect of intravenous and intra-arterially administered calcitonin gene-related peptide (CGRP) on the human forearm blood flow and cutaneous blood flow were investigated by means of venous occlusion plethysmography and laser-Doppler flowmetry, respectively. Infusion of CGRP (11-216 pmol min-1) into the brachial artery resulted in a dose-dependent increase in forearm blood flow and cutaneous blood flow which persisted for up to 90 min after the infusion was stopped. Repeated infusions resulted in an identical response. Systemic intravenous infusion of CGRP (104-520 pmol min-1) resulted in a dose-dependent flush in the face, neck, upper trunck and upper arms, and an increase in the forearm blood flow. The cutaneous blood flow was dramatically increased on the forehead, whereas on the hand only a slight increase was noted. By intravenous infusions a significant drop in blood pressure and increase in heart rate were seen at 520 pmol min-1. Thus, it is possible to give CGRP in doses that increase the blood flow in muscle and skin without resulting in a fall in systemic arterial blood pressure and tachycardia, suggesting that CGRP may be used as a tool for the treatment of various conditions in man with compromised blood flow.

Islet amyloid polypeptide and calcitonin gene-related peptide immunoreactivity in amyloid and tumor cells of canine pancreatic endocrine tumors

Seven canine pancreatic endocrine tumors were evaluated immunohistochemically for the presence of islet amyloid polypeptide (IAPP), calcitonin gene-related peptide (CGRP), and several other pancreatic hormones. Four tumors contained cells with IAPP immunoreactivity, and four had cells with CGRP immunoreactivity. IAPP and CGRP immunoreactivities were localized to distinctly different cell populations in three tumors in which both peptides were detected; however, IAPP immunoreactivity consistently was found in cells that also contained insulin immunoreactivity. Amyloid deposits, which were found in three of the seven tumors, showed strong immunoreactivity with antiserum against IAPP and weaker immunoreactivity with antiserum to CGRP. These results indicate that amyloid deposits in canine pancreatic endocrine tumors are likely derived from IAPP, as is amyloid found in human pancreatic endocrine tumors and pancreatic islet amyloid in aged and diabetic persons and cats.

Distinct hemodynamic and renal effects of calcitonin gene-related peptide and calcitonin in men

Cardiovascular and renal actions of human calcitonin gene-related peptide II (or beta) (CGRP) and of human calcitonin (CT) infused intravenously for 1 h each (79 and 263 pmol.kg-1.h-1) have been compared in normal men (n = 10 for CGRP, n = 6 for CT and vehicle alone). CGRP lowered diastolic blood pressure by 26% and increased the heart rate by 35% and raised plasma levels of norepinephrine, epinephrine, and dopamine and renin activity (P less than 0.01). The fractional excretion rates (FE) of sodium and chloride were doubled (P less than 0.05-0.01) in the presence of an unaltered glomerular filtration rate. CT, on the other hand, did not affect the diastolic blood pressure, but the stimulation of diuresis and of the FE of sodium and chloride was more pronounced with CT than with CGRP (P less than 0.01). Moreover, CT lowered serum calcium levels and stimulated urinary adenosine 3',5'-cyclic monophosphate and phosphate excretion (P less than 0.01). In conclusion, the cardiovascular effects of CGRP are contrasted by weaker renal tubular actions of the neuropeptide in relation to CT.

Regional haemodynamic effects of human alpha- and beta-calcitonin gene-related peptide in conscious Wistar rats

1. A comparative study was carried out to assess the regional haemodynamic effects of intravenous infusion of human alpha- and beta-calcitonin gene-related peptide (CGRP; 0.006, 0.06 and 0.6 nmol h-1) in conscious, unrestrained Wistar rats. 2. With human alpha-CGRP, tachycardia was always accompanied by a fall in mean arterial blood pressure (MBP), but human beta-CGRP at the middle dose caused tachycardia with no significant hypotension. 3. Human alpha- and beta-CGRP both caused dose-dependent falls in MBP accompanied by common carotid and hindquarters vasodilatations and increased flows. The highest dose of alpha- and beta-CGRP caused mesenteric vasoconstriction and renal vasodilatation, but the latter was not associated with an increase in flow. 4. With the intermediate dose, human alpha-CGRP caused more significant haemodynamic changes than did human beta-CGRP. In addition, comparison with previous experiments involving infusion of rat alpha-CGRP indicated that human alpha-CGRP had more potent haemodynamic effects than the former.

Effects of intravenous calcitonin gene-related peptide (CGRP) on local blood flow in the cat

The effects of i.v. calcitonin gene-related peptide (CGRP) on regional blood flow, vascular resistance, heart rate and cardiac output in cats were studied using the microsphere method. Three series of experiments were performed. In the first there was no pre-treatment of the animals. In the second the animals were pre-treated with indomethacin (5 mg kg-1) in order to prevent the formation of prostaglandins. In the third series the ganglionic blocking agent hexamethonium bromide (80 mg kg-1) was given in order to prevent autonomic reflexes. CGRP was given as an i.v. infusion. Two doses were tested in each series. Animals with no pre-treatment and those pre-treated with indomethacin received first 60 pmol kg-1 infused over a 5-min period and then 180 pmol kg-1 infused over a 3-min period. Animals under ganglionic blockade received the same dose as the total infusions in the other series (240 pmol kg-1) infused over 4 min and a second infusion of 1.2 nmol kg-1 over 5 min. Vasodilatory effects were observed in most of the tissues tested, but there were marked differences in sensitivity. The most sensitive tissues seemed to be the lacrimal, submandibular and parotid glands, the nictitating membrane, the tongue and the gallbladder. The patterns of sensitivity were similar in all the series, indicating that neither prostaglandins nor autonomic reflexes were involved in the effects. In experiments with animals under ganglionic blockade, an increase in blood pressure, concomitant with an increase in heart rate, was seen 5 min after the infusions ended. Thus, it is likely that the peptide exerts a direct positive chronotropic effect on the feline heart.

Effects of calcitonin gene-related peptide on canine cerebral artery strips and the in-vivo vertebral blood flow in dogs

The effects of calcitonin gene-related peptide (CGRP) on canine cerebral arteries and on vertebral blood flow were investigated in-vivo and in-vitro and the findings compared with the effects of vasoactive intestinal peptide (VIP) and substance P. Administration of CGRP into the vertebral artery caused a dose-dependent and long-lasting increase in blood flow. The in-vivo vasodilatory effects of substance P and VIP were short-lasting. CGRP (0.1 to 100 nmol/l) elicited a concentration-dependent relaxation of the isolated middle cerebral and basilar arteries when the tissues were precontracted by exposure to prostaglandin F2 alpha (PGF2 alpha). This effect was not antagonized by propranolol, atropine, tetrodotoxin, (N-Ac-Tyr1, D-Phe2)-growth hormone-releasing factor(1-29)-NH2 or (D-Pro2, D-Trp7,9) substance P. CGRP also reduced concentration-dependently the contraction of cerebral arteries induced by KCl or 9,11-epithio-11,12-metano-thromboxane A2 (STXA2). Mechanical removal of the endothelium did not abolish the vasodilatory response to CGRP. In PGF2 alpha-contracted canine cerebral arteries, VIP (0.1 to 100 nmol/l) was less potent a vasodilator than CGRP. At low concentrations (0.01 to 1 nmol/l) substance P elicited a rapid and short-lasting relaxation, and in the absence of endothelium this relaxation disappeared. These findings are clear evidence that CGRP modulates vascular tone.

Cardiovascular responses to intravenous calcitonin gene-related peptide (CGRP) in the albino rabbit

The regional sensitivity of different vascular beds to i.v. CGRP was investigated in the albino rabbit by using the microsphere method. Experiments were performed without pre-treatment on both conscious and pentobarbital-anaesthetized animals. In addition, in one series on conscious animals, rabbits were pre-treated with indomethacin in order to reduce the formation of prostaglandins. In another series, anaesthetized rabbits were subjected to ganglionic blockade with hexamethonium bromide in order to abolish reflexes involving the autonomic nervous system. 120 pmol kg-1 of CGRP was given to all the animals, the conscious animals receiving the peptide in one infusion lasting 4 min. In the anaesthetized animals, the dose was divided into first a 5-min infusion of 30 pmol kg-1 followed some minutes later by a 3-min infusion of 90 pmol kg-1. The most pronounced vasodilatory effects were seen in the pancreas, gallbladder, stomach, duodenum, tongue, teeth and the conjunctiva/nictitating membrane. In some series marked effects were also seen in the dura mater, choroid plexus and some parts of the brain. In the anaesthetized animals almost no statistically significant effects on local blood flows were seen following the first, smaller, dose, but following the larger dose more pronounced effects were observed. Pre-treatment with indomethacin did not to any great extent affect the responses, which contradicts the involvement of prostaglandins. The pattern of the responses was unaffected by the ganglionic blockade, but the variability of response was reduced. In conclusion there are great regional variations in the sensitivity to circulating CGRP. The patterns shows a resemblance to that obtained in other species, but there are some marked differences, The tissues most susceptible to the peptide are those easily exposed to noxious stimuli and containing CGRP in the sensory nerve endings, observations in agreement with the proposed role for the peptide in neurogenic defence mechanisms.

Calcitonin gene products and the kidney

Calcitonin gene-related peptide (CGRP) is localized in capsaicin-sensitive nerve fibres in the kidney and urogenital tract whereas calcitonin reaches the kidney through the general circulation. Systemic infusion of CGRP and perfusion of isolated rat kidney reduces vascular resistance, and increases renal blood flow and glomerular filtration. CGRP stimulates renin secretion in vivo and in vitro and inhibits contraction of isolated rat mesangial cells by angiotensin II. Calcitonin does not affect vascular resistance, renal blood flow and glomerular filtration, and is less potent in stimulating renin secretion, and does not alter contraction of isolated rat mesangial cells by angiotensin II. CGRP also exerts renal tubular effects brought about probably through interaction with calcitonin receptors. To this end, increased excretion of sodium and chloride, and stimulation of urinary flow are less pronounced with CGRP than with calcitonin. Calcitonin, moreover, stimulates the fractional urinary excretion of calcium and phosphate.

Renal mesangium is a target for calcitonin gene-related peptide

Rat calcitonin gene-related peptide (CGRP alpha; EC50, 1 nM) was shown to stimulate cAMP formation in cultured rat renal mesangial cells. CGRP concentration dependently (EC50, 1 nM) also inhibited contraction of mesangial cells by angiotensin II (10 nM). Angiotensin II (10 nM) caused a transient increase of the intracellular calcium concentration from 140 nM to 480 nM in the mesangial cells, but these calcium transients were not altered by CGRP. CGRP (10 nM) decreased vascular resistance in the isolated rat kidney perfused at constant pressure (100 mm Hg; P less than 0.01). The decreased vascular resistance was accompanied by a rise of the glomerular filtration fraction. CGRP, moreover, attenuated the effects of angiotensin II on renal vascular resistance and glomerular filtration (P less than 0.01). In conclusion, CGRP causes relaxation of renal mesangial cells and decreases renal vascular resistance. As a result CGRP raises glomerular filtration and the filtration fraction. The effect may be linked to cyclic AMP formation. Thus, regulation of renal vascular and glomerular function may represent a novel action of CGRP apart from its cardiovascular effects.

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.

The relaxant properties of human calcitonin gene-related peptide on vascular and extravascular capsular) smooth muscle of the isolated blood-perfused spleen of the anaesthetized dog

1. The 37 amino acid human calcitonin gene-related peptide (CGRP), was injected intra-arterially into the isolated, blood perfused spleen of the dog. 2. The only vascular response observed to CGRP, once threshold had been reached (10-20 fmol), was a dose-dependent splenic arterial vasodilatation. 3. The mean intra-arterial bolus dose of CGRP to reduce the splenic arterial vascular resistance by 50% of maximum response was 0.52 +/- 0.12 pmol. This value was significantly lower than the ED50 for the non-selective beta-adrenoceptor agonist isoprenaline (P less than 0.01) in the same experiments. CGRP is the most potent splenic vasodilator yet tested. 4. The mean maximum vasodilator response to CGRP was significantly less (P less than 0.001) than that achieved with isoprenaline. 5. The time course of the splenic arterial vascular response to CGRP was substantially longer than that to isoprenaline. 6. The splenic vasodilator response to CGRP was not altered by the prior administration of the selective beta 2-adrenoceptor antagonist, ICI 118,551. 7. At all doses of CGRP that caused splenic vasodilatation there were substantial increases in spleen volume. The time course of the response and slope of the regression line suggested an active capsular relaxation component. 8. In view of its location within the spleen and high molar potency, CGRP may be considered as a potential factor in the local control of the circulation through the spleen.

Calcitonin gene-related peptides I and II and calcitonin: distinct effects on gastric acid secretion in humans

The human calcitonin gene-related peptides I and II (CGRP I and CGRP II) are two neuropeptides that have been recognized throughout the gastrointestinal system including the stomach. The present study was undertaken to compare in healthy volunteers the effects of intravenous infusions of CGRP I and CGRP II (79 pmol/kg.h) on pentagastrin-stimulated acid secretion to those of calcitonin (88 pmol/kg.h). Calcitonin gene-related peptide I did not inhibit basal or pentagastrin-stimulated acid secretion. However, CGRP II and calcitonin inhibited pentagastrin-stimulated acid responses by 20% and 28%, respectively (p less than 0.05 and p less than 0.01), whereas basal acid output was only reduced with calcitonin (p less than 0.05). These effects were recognized with low doses of pentagastrin, and absent with high doses suggesting competitive inhibition. Furthermore, step-doses of CGRP I and CGRP II (79-320 pmol/kg.h) were given intravenously on continuous pentagastrin stimulation and compared with calcitonin (88-352 pmol/kg.h). Calcitonin gene-related peptide II and calcitonin induced a dose-dependent decrease of acid output, whereas CGRP I was ineffective. The inhibitory effects of CGRP II and calcitonin are not due to increased gastric alkaline secretion or to somatostatin release, as neither peptide stimulated gastric bicarbonate secretion or induced an increase in circulating somatostatin. In conclusion, CGRP II, unlike CGRP I, inhibits gastric acid secretion in humans. Inhibitory effects of CGRP II and of calcitonin were comparable. The results imply that CGRP I and II, at the level of the stomach, have distinct biological properties in humans.

Positive inotropic effect of calcitonin gene-related peptide mediated by cyclic AMP in guinea pig heart

The mechanism of cardiac actions of rat calcitonin gene-related peptide (CGRP) was analyzed on isolated guinea pig hearts. CGRP exerted a positive inotropic effect in a dose-dependent manner on the electrically driven left atria but not on the ventricles. Immunohistochemical studies demonstrated that CGRP-like immunoreactive nerves were distributed densely in the myocardia of the atria but only sparsely in those of the ventricles. The CGRP-induced augmentation of the contraction was accompanied by the shortening of the time to peak force and the increase in the relaxation velocity. The positive inotropic response to CGRP was significantly enhanced by isobutylmethylxanthine and was attenuated by adenosine. CGRP increased the action potential amplitude and prolonged action potential duration at the level of 50% repolarization in the left atria. In the preparations, which were partially depolarized with an increase in extracellular potassium, CGRP induced slow response action potentials. These electrophysiological results indicate that CGRP causes an increase in the slow inward Ca2+ current. The cyclic AMP content in the left atria significantly increased following the addition of CGRP, the time course of which was nearly consistent with that of the augmentation of the contractile force. In the membrane preparation of the atria, the activity of adenylate cyclase was enhanced by CGRP in a dose-dependent manner. These effects of CGRP are qualitatively similar to those of beta-adrenoceptor stimulation. It is concluded that the CGRP-induced response in the guinea pig atria is attributed to the activation of adenylate cyclase via stimulation of its specific receptor and the subsequent increase in the intracellular cyclic AMP level.

Positive inotropic effects and receptors of calcitonin gene-related peptide (CGRP) in porcine ventricular muscles

Calcitonin gene-related peptide (CGRP) in porcine ventricular muscles. positive inotropic effects in the isolated, electrically driven false tendon of the porcine heart. Specific CGRP-binding sites were present in solubilized membrane fractions; the dissociation constant (Kd) and the maximum binding (Bmax) were 50.4 pM and 180 fmol/mg protein, respectively. SDS-PAGE analysis of CGRP-binding sites revealed the molecular mass of 70 K and 120 K. Few CGRP-like immunoreactive nerves were present in the ventricular muscle layer. These results indicate that CGRP activates specific receptor sites on the ventricular muscles and causes positive inotropic responses. CGRP receptors in ventricles are likely to be activated by circulating CGRP.

Calcitonin gene-related peptide is a stimulator of renin secretion

Calcitonin gene-related peptide (CGRP) was found to stimulate renin secretion in vivo in normal human volunteers. Moreover, CGRP stimulated the release of renin in vitro from isolated rat renal juxtaglomerular cells (half-maximal effective concentration [EC50] 100 nM) concomitant with stimulation of cAMP production (EC50 60 nM). Immunoreactive CGRP was recognized in rat renal cortical nerve fibers, and intact rat CGRP was identified in extracts of the rat renal cortex. Because CGRP containing sensory nerve fibers are seen in the region of the juxtaglomerular apparatus, it would seem that the release of CGRP from these afferent nerves may be involved in the physiological control of renin secretion.

Identification of a receptor for calcitonin gene-related peptides I and II in human cerebellum

Receptor proteins for human calcitonin gene-related peptide (CGRP) have been demonstrated in the human cerebellum. Membrane homogenates were incubated with [125I] iodo CGRP-I and -II ([125I]CGRP). The bound radioligands were cross-linked to membrane proteins. Solubilized membrane proteins were separated by gel-electrophoresis. Autoradiography of the gels revealed specifically labeled ligand-protein complexes of Mr 17,500 and 54,000 for human CGRP-I and -II. Specific binding of [125I]CGRP-I and -II was only minimally affected by up to 0.5 microM salmon and human calcitonin. The affinity and specificity of CGRP-I and -II binding were the same in crude homogenates and in the purified binding proteins. In conclusion, indistinguishable binding proteins for [125I]CGRP-I and -II of 13,700 and 50,000 Da have been identified in the human cerebellum.

Calcitonin gene-related peptide: release by capsaicin and prolongation of the action potential in the guinea-pig heart

The mechanisms underlying the stimulatory effects of capsaicin on the contractility of the guinea-pig heart were studied in vitro. Capsaicin (10(-7) to 10(-5) M) caused an increased overflow of immunoreactive material, suggesting release of calcitonin gene-related peptide (CGRP)-and neurokinin A (NKA)-like immunoreactivity (-LI), but not of neuropeptide Y (NPY)-LI from the isolated Langendorff-perfused whole heart. The capsaicin-induced release was calcium-dependent. During exposure to capsaicin, the heart rate was increased, while the contractile force was reduced. In addition to releasing CGRP and NKA-LI, potassium (60 mM) also increased the overflow of NPY-LI. The potassium-induced release of peptides was less calcium-dependent than the response to capsaicin. Considerably higher tissue levels of CGRP-LI were found in the atria (about 30 pmol g-1) than in the ventricles (about 10 pmol g-1). In experiments on the right atria using transmembrane action-potential recordings of myocytes, CGRP induced a prolongation of the action potential concomitantly with an increase in rate and contractile force, which was similar to the effect of noradrenaline. Furthermore, CGRP increased the contractile force and relaxation velocity of the electrically stimulated atria. Capsaicin (10(-7) M) also increased the duration of the atrial action potential. In conclusion, CGRP-like material is released by capsaicin from the isolated guinea-pig heart. Both CGRP and capsaicin prolong the plateau phase of the action potential of atrial myocytes. Therefore, the present data give further evidence that CGRP release from sensory nerves within the heart underlies the cardiostimulatory actions of capsaicin.

Calcitonin gene-related peptide but not substance P mimics capsaicin-induced coronary vasodilation in the pig

The vasodilator effects of the human calcitonin gene-related peptides alpha (hCGRP alpha) and beta (hCGRP beta) were studied in vitro and in vivo in relation to the effects of substance P (SP) and capsaicin on coronary vascular tone in the pig. Both hCGRP alpha and -beta induced a concentration-dependent, long-lasting relaxation of precontracted small (diameter 0.5 mm) pig coronary arteries in vitro. SP was slightly more potent but caused a transient relaxation with a smaller maximal response than CGRP. The relaxation induced by hCGRP alpha and -beta as well as SP was resistant to propranolol and atropine. Capsaicin also induced a long-lasting relaxation of potassium and PGF2 alpha-precontracted coronary arteries. After tachyphylaxis to SP had developed the relaxant effects of CGRP and capsaicin were unchanged. Rubbing the vessels to remove the endothelium completely abolished the relaxant effects of SP while the vasodilation induced by hCGRP alpha as well as capsaicin remained unchanged. Injections of hCGRP alpha, SP or capsaicin into the constantly perfused left anterior descending coronary artery of the pig in vivo caused a dose-dependent decrease in perfusion pressure, suggesting coronary vasodilation. In conclusion, the vasodilator effects of SP in vitro differ from the response to CGRP both with regard to their transient nature, the development of tachyphylaxis and endothelium dependence. The capsaicin-induced coronary vasodilation is therefore more likely to depend on release of CGRP rather than tachykinins from sensory nerves since neither endothelium removal nor SP-tachyphylaxis influenced the capsaicin and CGRP responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of binding sites for the calcitonin gene-related peptides I and II in man

Specific and saturable binding sites of the synthetic human calcitonin gene-related peptide-I (CGRP-I) and -II (CGRP-II) have been identified in membrane homogenates of the human central nervous system, heart and spleen. Half maximal inhibition of the binding of 125I-CGRP-II was achieved with 0.25 nM and 1.7 nM of non-radioactive CGRP-I or -II, and with 260 and 850 nM salmon calcitonin in the spinal cord and cerebellum, respectively, but 1 microM human calcitonin was not recognized. Autoradiographs of diencephalic sections revealed different distribution of 125I-CGRP-I and -II binding sites.