Calcitonin Gene-related Peptide Outflow Research Articles

Tapentadol inhibits calcitonin gene-related peptide release from rat brainstem in vitro

We have previously developed an in vitro model of rat brainstem explants. The latter release sizable amounts of calcitonin gene-related peptide (CGRP); basal release can be stimulated by such secretagogues as high KCl concentrations, veratridine or capsaicine. In this paradigm we investigated the activity of the analgesic agent tapentadol; the effects of tapentadol were compared to those of a classical opioid receptor agonist, morphine, and the selective noradrenaline reuptake inhibitor reboxetine. Morphine inhibited basal CGRP release, with statistical significance from 1nM onward and maximal (−44%) inhibition at 100μM. Morphine also inhibited K+-stimulated peptide release, with a significant effect from 1μM and maximal (−39%) decrease at 100μM, but failed to inhibit release stimulated by 10μM capsaicin. At variance, reboxetine had no effect on baseline CGRP outflow, but was able to inhibit both K+-stimulated [significant inhibition from 1μM onward and maximal (−37%) decrease at 100μM], and capsaicin-stimulated release [significant effect from 1μM and maximal (−31%) decrease at 100μM]. Likewise, tapentadol had no effect on baseline CGRP release up to 100μM, but decreased secretion stimulated by 56mM KCl or capsaicin, with significant effects from 0.1 and 1μM respectively; maximal inhibition over 56mM KCl and capsaicin stimuli was −29% and −31%, respectively. Naloxone antagonized the effect of morphine, but not those of reboxetine and tapentadol, on K+-stimulated CGRP secretion. In conclusion the present study provides consistent pharmacological evidence that tapentadol acts as a noradrenaline reuptake inhibitor agent in this experimental model.

Dopamine receptor antagonists prevent the d-amphetamine-induced increase in calcitonin gene-related peptide levels in ventral striatum.

Microdialysis in conjunction with radioimmunoassay (RIA) were used to study the effects of acute d-amphetamine or dopamine (DA) receptor antagonists administration on extracellular concentrations of calcitonin gene-related peptide (CGRP) in the ventral striatum of the rat. One hour after the subcutaneous (s.c.) injection of saline, the DA-D(1) receptor antagonist SCH 23390 (0.3 mg/kg) or the DA-D(2/3) receptor antagonist raclopride (1.0 mg/kg), one additional s.c. injection of saline or d-amphetamine (1.5 mg/kg) was given. The dialysates were collected at 60-min intervals; CGRP-like immunoreactivities (-LI) were determined by RIA. d-Amphetamine significantly increased extracellular CGRP-LI concentrations compared to the control animals. Administration of either SCH 23390 or raclopride did not significantly affect CGRP-LI concentrations. Pretreatment with either SCH 23390 or raclopride abolished the stimulatory effect of d-amphetamine on CGRP-LI levels. The results show that d-amphetamine administration results in an increase in extracellular concentrations of CGRP in the ventral striatum through a mechanism that appears to involve stimulation of either DA-D(1) or DA-D(2/3) receptors. The results also indicate that changes in dopaminergic neurotransmission affect CGRP outflow in the ventral striatum in a phasic but not tonic manner.

Myocardial outflow of calcitonin gene-related peptide in relation to metabolic stress during coronary artery bypass grafting without cardiopulmonary bypass

Objective: Because of adverse effects of cardiopulmonary bypass and the prospect of shortening intensive care and hospital stay, coronary artery bypass grafting without cardiopulmonary bypass is gaining increased attention. The impact of the localized myocardial ischemia that is inherent in these procedures has not been thoroughly investigated in human beings. We have investigated metabolic changes, possible myocardial damage, and myocardial outflow of the vasodilator calcitonin gene-related peptide during coronary artery bypass grafting without cardiopulmonary bypass. Methods: Coronary sinus and arterial blood was sampled before coronary arterial occlusion, after 10 minutes of ischemia, and after 1 and 10 minutes of reperfusion in 9 consecutive patients (mean age 70 ± 5 years) who had an anastomosis performed to the left anterior descending artery without cardiopulmonary bypass. Results: No perioperative myocardial infarctions occurred. The arteriovenous difference in lactate decreased during ischemia, to reach a minimum after 1 minute of reperfusion (–0.17 ± 0.25 vs 0.15 ± 0.25 mmol/L before ischemia; P = .008). Myocardial lactate extraction decreased (from 11.2 ± 13.6 μmol/min before ischemia to –3.0 ± 7.0 μmol/min after 1 minute of reperfusion; P = .012), that is, a net production of lactate. The arteriovenous difference in calcitonin gene-related peptide decreased from –0.1 ± 2.6 pmol/L before ischemia to –30.5 ± 26.5 pmol/L ( P = .008) after 1 minute of reperfusion. Conclusions: The localized myocardial ischemia associated with these procedures causes metabolic changes in the myocardium, but no myocardial damage. The ischemia-related outflow of calcitonin gene-related peptide indicates that the vasodilating and cardioprotective properties of this peptide that are known from animal studies may be of importance in myocardial ischemia in human beings. (J Thorac Cardiovasc Surg 1999;117:447-53)

Release and effects of calcitonin gene-related peptide in myocardial ischaemia

This thesis is based on the following papers, which will be referred to by their Roman numerals. I. Franco-Cereceda A, Källner G, Lundberg JM: Capsazepine-sensitive release of calcitonin gene-related peptide from C-fibre afferents in the guinea-pig heart by low pH and lactic acid. Eur J Pharmacol 1993;238:311-316. II. Franco-Cereceda A, Källner G, Lundberg JM: Cyclo-oxygenase products released by low pH have capsaicin-like actions on sensory nerves in the isolated guinea pig heart. Cardiovasc Res 1994;28:365-369. III. Källner G, Franco-Cereceda A: Attenuation of low pH-, but not capsaicin- or PGI-evoked CGRP-release by endothelium removal using saponin. Acta Physiol Scand 1995;155:251-256. IV. Källner G, Franco-Cereceda A: Ion channels involved in the release of calcitonin generelated peptide by low pH, prostacyclin and capsaicin in the isolated guinea-pig heart. Eur J Pharmacol 1998;in press. V. Källner G, Gonon A, Franco-Cereceda A: Calcitonin gene-related peptide in myocardial ischaemia and reperfusion in the pig. Cardiovasc Res 1998;38:493-499. VI. Källner G, Franco-Cereceda A: Aggravation of myocardial infarction in the porcine heart by capsaicin-induced depletion of calcitonin gene-related peptide (CGRP). J Cardiovasc Pharmacol , accepted for publication. VII. Källner G, Öwall A, Franco-Cereceda A: Myocardial outflow of calcitonin gene-related peptide in relation to metabolic stress during coronary artery bypass grafting without cardiopulmonary bypass. Submitted for publication.

232 A protective effect of nicotine against glutamate neurotoxicity in cultured rat retinal neurons

We have investigated the ability of Ruthenium Red, an inorganic dye with calcium entry blocking properties, to interfere with the ‘efferent’ function of capsaicin-sensitive sensory nerves. These nerves were activated in the guinea-pig isolated bronchus (atropine in the bath) or left atria (reserpine-pretreated animals, atropine in the bath) by electrical field stimulation or with capsaicin. Both stimuli produced a contraction of the bronchus and a positive inotropic response in the atria, responses which are mediated by endogenous neuropeptides (tachykinins in the bronchus, calcitonin gene-related peptide in the atria) released from sensory nerves. Ruthenium Red (10 μM for 20 min in the cases) selectively inhibited the responses produced by the administration of capsaicin, while leaving the responses to electrical field stimulation unaffected. Likewise, the bronchonconstrictor response to exogenous neurokinin A and the atrial positive inotropic response to calcitonin gene-related peptide were unaffected by Ruthenium Red. A prejunctional site of action Ruthenium Red was confirmed in release experiments where the dye strongly inhibited the capsaicin-evoked outflow of calcitonin gene-related peptide, which is taken as a marker of activation in sensory nerves. Together with other observations, these findings support the concept that there are two independent mechanisms for activating the ‘efferent’ function of sensory nerves, one of which is activated by capsaicin and is Ruthenium Red-sensitive but ω-conotoxin-resistant, while the other is activated by propagated action potentials (field stimulation) and is ω-conotoxin-sensitive and Ruthenium Red-resistant.

A protective effect of nicotine against glutamate neurotoxicity in cultured rat retinal neurons

We have investigated the ability of Ruthenium Red, an inorganic dye with calcium entry blocking properties, to interfere with the ‘efferent’ function of capsaicin-sensitive sensory nerves. These nerves were activated in the guinea-pig isolated bronchus (atropine in the bath) or left atria (reserpine-pretreated animals, atropine in the bath) by electrical field stimulation or with capsaicin. Both stimuli produced a contraction of the bronchus and a positive inotropic response in the atria, responses which are mediated by endogenous neuropeptides (tachykinins in the bronchus, calcitonin gene-related peptide in the atria) released from sensory nerves. Ruthenium Red (10 μM for 20 min in the cases) selectively inhibited the responses produced by the administration of capsaicin, while leaving the responses to electrical field stimulation unaffected. Likewise, the bronchonconstrictor response to exogenous neurokinin A and the atrial positive inotropic response to calcitonin gene-related peptide were unaffected by Ruthenium Red. A prejunctional site of action Ruthenium Red was confirmed in release experiments where the dye strongly inhibited the capsaicin-evoked outflow of calcitonin gene-related peptide, which is taken as a marker of activation in sensory nerves. Together with other observations, these findings support the concept that there are two independent mechanisms for activating the ‘efferent’ function of sensory nerves, one of which is activated by capsaicin and is Ruthenium Red-sensitive but ω-conotoxin-resistant, while the other is activated by propagated action potentials (field stimulation) and is ω-conotoxin-sensitive and Ruthenium Red-resistant.

Nicotine and acetylcholine induce release of calcitonin gene-related peptide from rat trachea

In the present study, we observed that nicotine, the nicotinic analogue cytisine, and acetylcholine (ACh) evoked a concentration-dependent (5 x 10(-6)-5 x 10(-5) M) release of calcitonin gene-related peptide (CGRP) from the rat trachea. After a prolonged exposure to capsaicin, nicotine-induced CGRP release was absent, suggesting that the release of CGRP by nicotine is derived from capsaicin-sensitive afferent terminals. Nicotine- and cytisine-induced release displayed a significant degree of tachyphylaxis after sequential exposures. The release of CGRP evoked by capsaicin was also reduced after nicotine and cytisine desensitization. This indicates that similar mechanisms may mediate the tachyphylactic effect of capsaicin and nicotine. Hexamethonium and mecamylamine blocked the effect of nicotine but not that of ACh, whereas atropine significantly attenuated the release of CGRP outflow induced by ACh. Physostigmine and neostigmine did not alter resting release of CGRP from rat trachea, although exogenous (10(-5) M) ACh-induced CGRP release was enhanced in the presence of neostigmine, suggesting minimal tonic cholinergic activity in this model. We conclude that activation of nicotinic and muscarinic receptors in the rat trachea can induce local release of CGRP. These observations indicate that cholinergically induced airway responses may be mediated in part by activation of the peripheral terminals of primary afferent sensory neurons and subsequent release of local neuropeptides.

Cyclo-oxygenase products released by low pH have capsaicin-like actions on sensory nerves in the isolated guinea pig heart.

Previous work has shown that ischaemia releases calcitonin gene related peptide (CGRP) from capsaicin sensitive nerve terminals in the perfused heart. Prostacyclin (PGI2) is also released during ischaemia. The aim of this study was to investigate whether the release of CGRP by low pH and lactic acid was associated with PGI2 formation and if PGI2 mediated its effect through capsaicin receptors which could be inhibited by capsazepine. The isolated Langendorff perfused guinea pig heart was used with a constant perfusion pressure of 70 cm H2O. Low pH was accomplished by changing the Tyrode solution to buffers with pH 7, 6, and 5, or lactic acid (5 mM with pH 6.9). The outflow of CGRP and the stable PGI2 metabolite 6-keto-PGF1 alpha was measured by radioimmunoassay. Low pH (pH 7, 6, 5) and lactic acid evoked release of CGRP. At moderate acidosis (pH 7 and 6) the CGRP release was dependent on extracellular Ca2+, while at pH 5 approximately half of the peptide release persisted in the absence of extracellular Ca2+. This release was attenuated by diclofenac or indomethacin, two inhibitors of prostaglandin formation, as well as by the capsaicin receptor antagonist capsazepine. Both arachidonic acid and PGI2, the predominant cyclo-oxygenase product formed during myocardial ischaemia, evoked a capsazepine sensitive release of CGRP, while capsazepine did not influence the formation of PGI2 evoked by low pH or arachidonic acid. In the isolated guinea pig heart, moderate acidosis is associated with CGRP release dependent on influx of extracellular Ca2+ and formation of PGI2, with subsequent stimulation of capsazepine sensitive receptors. With more severe acidosis there is an additional non-PGI2-linked CGRP release. Capsazepine represents a novel pharmacological principle for inhibiting the effects of prostanoids on sensory nerves without influencing their formation.

Modulation of calcitonin gene-related peptide release evoked by bradykinin and electrical field stimulation in guinea-pig atria

Electrical field stimulation (EFS) and bradykinin (BK) are able to activate capsaicin-sensitive sensory neurons of guinea-pig atria in a ω-contoxin (CTX)-sensitive and Ruthenium Red (RR)-insensitive manner. The aim of this work was to study EFS and BK-induced release of calcitonin gene-related peptide (CGRP) from guinea-pig atria and in particular the action of morphine and neuropeptide Y (NPY) on this release. EFS-induced CGRP release was frequency-dependent and tetrodotoxin (TTX)-sensitive, while BK-evoked CGRP release was TTX-insensitive. On the other hand, CGRP outflow induced by either EFS or BK was similarly reduced in the presence of morphine and NPY. It is therefore hypothesized that NPY and opioids exert their inhibitory action by acting on the very terminal region of the nerve fibre. Moreover, our results show that dermorphine but not dynorphin reduced BK-evoked CGRP release, suggesting that μ opioid receptors are responsible for morphine action. Studying the action of peptide YY and NPY (16–36) on BK-evoked CGRP release, we demonstrated that both had similar inhibitory effects, supporting the presence of Y 2 receptors on the nerve terminal region.

Pharmacology of the effects of bradykinin, serotonin, and histamine on the release of calcitonin gene-related peptide from C-fiber terminals in the rat trachea

The effects of inflammatory substances, bradykinin (BK), 5-HT, and histamine (HIS), on the release of calcitonin gene-related peptide (CGRP) from the peripheral terminals of sensory afferents in the rat trachea were examined ex vivo. With intralumenal perfusion, the isolated rat trachea displays low but measurable secretion of CGRP (32 +/- 4.6 fmol/10 min fraction). The addition of BK (10(-6) to 10(-4) M) to the superfusate resulted in an immediate, concentration-dependent increase in the level of CGRP (5-30-fold increase above baseline) in the perfusates, and this effect showed a concentration-dependent tachyphylaxis. [Des-Arg10]-kallidin, a B1 receptor agonist, at concentrations of up to 10(-4) M did not induce any significant increase in CGRP outflow from the rat trachea. HIS at 10(-4) M caused a modest but progressive augmentation in the release of CGRP. 5-HT at 10(-4) M had no effect upon the resting efflux of CGRP, but at a concentration of 10(-6) M significantly enhanced the release of CGRP evoked by capsaicin (10(-6) M). Similar conditioning studies carried out with HIS and BK showed no augmentation. BK-evoked CGRP efflux was significantly inhibited by [D-Arg0, Hyp3, Thi5,8, D-Phe7]-BK (B2 antagonist) and indomethacin. While [Des-Arg9, Leu8]-BK (B1 antagonist) also caused a reduction of BK-induced release, its effect did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the involvement of bradykinin in chemically-evoked cystitis in anaesthetized rats

The effect of Hoe 140, a potent bradykinin B2 receptor antagonist, on the micturition reflex and detrusor hyperreflexia induced by chemical cystitis has been investigated in anaesthetized rats. Hoe 140 (1-100 nmol/kg i.v.) produced a dose-dependent blockade of the contraction of the rat urinary bladder induced by i.v. administration of bradykinin (100 nmol/kg) without affecting the response produced by the selective tachykinin NK-1 receptor agonist, [Sar9] substance P (SP) sulfone (1 nmol/kg i.v.). At doses which produce selective and long-lasting blockade of bradykinin receptors in the urinary bladder, Hoe 140 did not modify urodynamic parameters in normal rats. Intravesical instillation of xylene in female rats decreased bladder capacity and increased micturition frequency. These effects also occurred in rats pretreated with capsaicin as adults. Hoe 140 did not modify xylene-induced cystitis. Intraperitoneal administration of cyclophosphamide (150 mg/kg, 48 h before) decreased bladder capacity and increased micturition frequency. These effects of cyclophosphamide were abolished in rats pretreated with capsaicin as adults. Hoe 140 increased bladder capacity and decreased micturition frequency in rats pretreated with cyclophosphamide. Addition of bradykinin (10 mumol/l) to the medium in the superfused rat urinary bladder preparation evoked a prompt increase in the outflow of calcitonin gene-related peptide like immunoreactivity (CGRP-LI). Hoe 140 (3 mumol/l) inhibited (by about 50%) the CGRP-LI out-flow stimulated by bradykinin. These findings demonstrate the participation of bradykinin, through B2 receptors, in the genesis of detrusor hyperreflexia during cyclophosphamide-induced cystitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine inhibits action potential-dependent release of calcitonin gene-related peptide- and substance P-like immunoreactivities from primary afferents in rat spinal cord

Electrical field stimulation (5 Hz) evoked a prompt outflow of calcitonin gene-related peptide- and substance P-like immunoreactivities (CGRP-LI and SP-LI, respectively) from superfused slices of the dorsal but not ventral half of the rat spinal cord. The evoked outflow was abolished by tetrodotoxin, calcium-free medium or previous exposure to capsaicin, indicating that it is produced through action potentials invading the central terminals of capsaicin-sensitive primary afferents. Adenosine as well as γ-aminobutyric acid (GABA) or the GABA B receptor agonist (—)-baclofen produced a concentration-dependent inhibition of the evoked CGRP-LI outflow. Adenosine also inhibited the evoked SP-LI outflow. These findings demonstrate that inhibition of transmitter release from primary afferent neurons should be considered as a possible mechanism of the antinociceptive action of adenosine and adenosine analogs.

Ruthenium‐red inhibits CGRP release by capsaicin and resiniferatoxin but not by ouabain, bradykinin or nicotine in guinea‐pig heart: correlation with effects on cardiac contractility

1. The possible influence of ruthenium-red (RR) on contractility and outflow of calcitonin gene-related peptide (CGRP)-like and neuropeptide Y (NPY)-like immunoreactivity (LI) from the heart of the guinea-pig induced by capsaicin, resiniferatoxin, nicotine, ouabain or bradykinin was studied in vitro. 2. In the isolated right atrium, exposure to capsaicin evoked an increase in contractile rate and tension simultaneously with an enhanced outflow of CGRP-LI, indicating release from the atria. Repeated administration of capsaicin induced tachyphylaxis. Incubation with RR markedly attenuated the capsaicin-evoked release of CGRP-LI while no clear-cut effects were seen on contractile tension or rate. 3. In the isolated whole heart, perfusion with capsaicin induced an increased outflow of CGRP-LI and stimulated heart rate, while a negative inotropic effect was observed. A second administration of capsaicin to the same preparations failed to influence the CGRP-LI outflow and in these experiments the positive chronotropic effect was absent while the negative inotropic action remained unchanged. Capsaicin-perfusion in the presence of RR failed to induce any increased outflow of CGRP-LI from the hearts or changes in contractile activity. However, after 1 h of rinsing with Tyrode solution repeated capsaicin perfusion in the absence of RR caused a clear-cut (60% of control) release of CGRP-LI and contractile responses were restored. 4. Perfusion with resiniferatoxin evoked a RR-sensitive, clear-cut increased CGRP-LI output without any effects on contractile force or heart rate. Repeated administration of resiniferatoxin induced tachyphylaxis with respect to outflow. Capsaicin perfusion after resiniferatoxin did not influence cardiac rate, force or CGRP-LI outflow suggesting development of cross-tachyphylaxis. 5. Perfusion with RR did not influence the outflow of CGRP-LI or contractility changes evoked by perfusion with nicotine, ouabain or bradykinin. In addition, the release of NPY-LI by nicotine remained unchanged in the presence of RR. Furthermore, the positive chronotropic effect of human CGRP alpha remained intact in the presence of RR. 6. It is concluded that RR selectively inhibits capsaicin- and resiniferatoxin-induced excitation of cardiac sensory nerves as revealed by inhibition of both CGRP-LI release and the cardiostimulatory action of capsaicin. RR also seems to protect the cardiac capsaicin-sensitive fibres from the development of tachyphylaxis to capsaicin. Finally, RR prevents the capsaicin-evoked negative inotropic effect which is not related to activation of sensory nerves.

Effects of colchicine on the development of tachyphylaxis to calcitonin gene-related peptide in the guinea pig heart

Calcitonin gene-related peptide (CGRP) induced a concentration-dependent positive inotropic and chronotropic effect on the spontaneously beating right atrium subject to tachyphylaxis upon extended incubation. This stimulatory effect was mimicked by capsaicin. After incubation with colchicine there was a marked attenuation of the decline in the prolonged response to CGRP or capsaicin and no development of CGRP tachyphylaxis. Colchicine incubation did not influence the capsaicin-induced stimulation of the frequency or CGRP outflow in whole heart preparations. Thus, the present data suggest that the development of CGRP tachyphylaxis is a specific receptor-mediated event which can be inhibited by colchicine, probably by disruption of membrane bound proteins.

Salivary neuropeptides as signs of specific action of nasal capsaicin

Electrical field stimulation (5 Hz) evoked a prompt outflow of calcitonin gene-related peptide- and substance P-like immunoreactivities (CGRP-LI and SP-LI, respectively) from superfused slices of the dorsal but not ventral half of the rat spinal cord. The evoked outflow was abolished by tetrodotoxin, calcium-free medium or previous exposure to capsaicin, indicating that it is produced through action potentials invading the central terminals of capsaicin-sensitive primary afferents. Adenosine as well as γ-aminobutyric acid (GABA) or the GABAB receptor agonist (—)-baclofen produced a concentration-dependent inhibition of the evoked CGRP-LI outflow. Adenosine also inhibited the evoked SP-LI outflow. These findings demonstrate that inhibition of transmitter release from primary afferent neurons should be considered as a possible mechanism of the antinociceptive action of adenosine and adenosine analogs.

The ‘efferent’ function of capsaicin-sensitive nerves: Ruthenium Red discriminates between different mechanisms of activation

We have investigated the ability of Ruthenium Red, an inorganic dye with calcium entry blocking properties, to interfere with the ‘efferent’ function of capsaicin-sensitive sensory nerves. These nerves were activated in the guinea-pig isolated bronchus (atropine in the bath) or left atria (reserpine-pretreated animals, atropine in the bath) by electrical field stimulation or with capsaicin. Both stimuli produced a contraction of the bronchus and a positive inotropic response in the atria, responses which are mediated by endogenous neuropeptides (tachykinins in the bronchus, calcitonin gene-related peptide in the atria) released from sensory nerves. Ruthenium Red (10 μM for 20 min in the cases) selectively inhibited the responses produced by the administration of capsaicin, while leaving the responses to electrical field stimulation unaffected. Likewise, the bronchonconstrictor response to exogenous neurokinin A and the atrial positive inotropic response to calcitonin gene-related peptide were unaffected by Ruthenium Red. A prejunctional site of action Ruthenium Red was confirmed in release experiments where the dye strongly inhibited the capsaicin-evoked outflow of calcitonin gene-related peptide, which is taken as a marker of activation in sensory nerves. Together with other observations, these findings support the concept that there are two independent mechanisms for activating the ‘efferent’ function of sensory nerves, one of which is activated by capsaicin and is Ruthenium Red-sensitive but ω-conotoxin-resistant, while the other is activated by propagated action potentials (field stimulation) and is ω-conotoxin-sensitive and Ruthenium Red-resistant.

Prostaglandins and CGRP release from cardiac sensory nerves

(1) The possible influence of prostaglandins (PG) E1 and I2 as well as ischaemia, ouabain and bradykinin on the outflow of calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-like immunoreactivity (LI) from the guinea-pig heart was studied in vitro. (2) Exposure to PGE1 (10(-5) M), but not PGI2 (10(-5) M), induced an increased outflow, suggesting release of CGRP-LI. PGE1 simultaneously increased the contractile force and heart rate while no effects were observed on perfusate volume or outflow of NPY-LI. PGI2 had no effect on contractile parameters or coronary flow. In separate experiments on capsaicin-pretreated animals, the stimulatory effects of PGE1 on heart rate and contractile force remained unchanged while no increased CGRP-LI outflow was detectable. (3) Ouabain, bradykinin and reperfusion after total stop-flow ischaemia was associated with an indomethacin-resistant increase in perfusate levels of CGRP-LI but not of NPY-LI. While ouabain markedly increased the contractile force, exposure to bradykinin or ischaemia did not induce any clear-cut changes in contractile force or heart rate. (4) Capsaicin-exposure evoked a markedly increased outflow of CGRP-LI but not of NPY-LI in combination with an increase in heart rate and a decrease in contractile force. Repeated administration of capsaicin induced tachyphylaxis. The stimulatory effects of capsaicin on CGRP-LI outflow and heart rate, but not the negative inotropic effect, did not occur in capsaicin-pretreated animals. (5) It is concluded that PGE1, but not PGI2, can activate cardiac capsaicin-sensitive fibres as revealed by increased outflow of CGRP-LI.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential release of calcitonin gene-related peptide and neuropeptide Y from the isolated heart by capsaicin, ischaemia, nicotine, bradykinin and ouabain.

The influence of various drugs as well as total ischaemia on the outflow of calcitonin gene-related peptide (CGRP), which is present in sensory nerves, and neuropeptide Y (NPY), which is co-stored with noradrenaline (NA), from the isolated guinea-pig heart, was studied in vitro. Capsaicin exposure and total ischaemia for 5-30 min induced a Ca2+-dependent increase in the outflow, suggesting release, of CGRP- but not NPY-like immunoreactivity (LI) from the heart. When characterized by high performance liquid chromatography (HPLC), the CGRP-LI present in heart extracts and the released CGRP-LI by capsaicin eluted in a major peak corresponding to synthetic CGRP. Incubation with morphine, indomethacin or reserpine pretreatment did not influence the capsaicin-evoked release of CGRP-LI. Capsaicin pretreatment depleted the cardiac content of CGRP-LI but not NPY-LI. The increase in perfusate volume observed after 30 min ischaemia in controls was reduced after capsaicin pretreatment. Nicotine exposure induced release of CGRP- as well as NPY-LI in a concentration- and Ca2+-dependent manner. The increased outflow of NPY-LI was not influenced by capsaicin pretreatment. Among other agents tested, bradykinin and ouabain caused increased outflow of CGRP but not of NPY-LI. Noradrenaline, tyramine, histamine, vasopressin, alpha,beta methylene ATP, ATP or adenosine induced changes in cardiac contractility or flow but did not evoke any detectable release of CGRP- or NPY-LI. In conclusion, the release of multiple neuropeptides can be studied in combination with contractile recordings using the isolated perfused guinea-pig whole heart preparation. Activation of cardiac sensory nerves by capsaicin, nicotine, bradykinin and ouabain, as well as ischaemia, induced release of CGRP while nicotine also evoked NPY release.