Anandamide induces cardiovascular and respiratory reflexes via vasosensory nerves in the anaesthetized rat

1. We tested the hypothesis that sensory nerves innervating blood vessels play a role in the local and systemic regulation of the cardiovascular and respiratory (CVR) systems. We measured CVR reflexes evoked by administration of anandamide (86 - 863 nmoles) and capsaicin (0.3 - 10 nmoles) into the hindlimb vasculature of anaesthetized rats. 2. Anandamide and capsaicin each caused a rapid dose-dependent reflex fall in blood pressure and an increase in ventilation when injected intra-arterially into the hindlimb. 3. Action of both agonists at the vanilloid receptor (VR1) on perivascular sensory nerves was investigated using capsazepine (1 mg kg(-1) i.a.) a competitive VR1 antagonist, ruthenium red (1 mg kg(-1) i.a.), a non-competitive antagonist at VR1, or a desensitizing dose of capsaicin (200 nmoles i.a.). The cannabinoid receptor antagonist SR141716 (1 mg kg(-1) i.a.) was used to determine agonist activity at the CB(1) receptor. 4. Capsazepine, ruthenium red, or acute VR1 desensitization by capsaicin-pretreatment, markedly attenuated the reflex CVR responses evoked by anandamide and capsaicin (P< 0.05; paired Student's t-test). Blockade of CB(1) had no significant effect on the responses to anandamide. 5. Local sectioning of the femoral and sciatic nerves attenuated CVR responses to anandamide and capsaicin (P< 0.05). Vagotomy or carotid sinus sectioning had no significant effect on anandamide- or capsaicin-induced responses. 6. These data demonstrate that both the endogenous cannabinoid, anandamide, and the vanilloid, capsaicin, evoke CVR reflexes when injected intra-arterially into the rat hindlimb. These responses appear to be mediated reflexly via VR1 located on sensory nerve endings within the hindlimb vasculature.

The plasma protein extravasation induced by adenosine and its analogues in the rat dorsal skin: evidence for the involvement of capsaicin sensitive primary afferent neurones and mast cells

1. The contribution of sensory neurons and mast cells to the oedema evoked by adenosine A1 (N(6)-cyclopentyladenosine, CPA, 3 - 30 nmol site(-1)), A2 (5'N-ethylcarboxamidoadenosine, NECA, 1 - 10 nmol site(-1)) and A3 receptor agonists (N6-[3-iodobenzyl]-N-methyl-5'-carboxiamidoadenosine, IB-MECA, 0.01 - 3 nmol site(-1)) was investigated in the rat skin microvasculature, by the extravascular accumulation of intravenously-injected (i.v.) 125I-albumin. 2. Intradermal (i.d.) injection of adenosine and analogues induced increased microvascular permeability in a dose-dependent manner (IB-MECA > NECA > CPA > adenosine). The non-selective adenosine receptor antagonist theophylline (5 - 50 nmol site(-1)) markedly inhibited adenosine, CPA or NECA but not IB-MECA-induced plasma extravasation. The A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 0.3 - 3 micromol kg(-1), i.v.) significantly reduced CPA-induced plasma extravasation whereas responses to adenosine, NECA or IB-MECA were unchanged. The A2 receptor antagonist 3,7-dymethyl-1-proprargylxanthine (DMPX, 0.5 - 50 nmol site(-1)) significantly reduced NECA-induced plasma extravasation without affecting responses to adenosine, CPA and IB-MECA. 3. The tachykinin NK1 receptor antagonist (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]octane chloride (SR140333), but not the NK2 receptor antagonist (S)-N-methyl-N[4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl]-benzamide (SR48968), significantly inhibited the plasma extravasation evoked by higher doses of adenosine (100 nmol site(-1)), CPA (100 nmol site(-1)), NECA (1 nmol site(-1)) and IB-MECA (0.1 - 1 nmol site(-1)). In rats treated with capsaicin to destroy sensory neurons, the response to higher doses of adenosine, CPA and NECA, but not IB-MECA, was significantly inhibited. 4. The effects of adenosine and analogues were largely inhibited by histamine and 5-hydroxytryptamine (5-HT) antagonists and by compound 48/80 pretreatment. 5. In conclusion, our results provide evidence that adenosine A1 and A2, but not A3, receptor agonists may function as cutaneous neurogenic pro-inflammatory mediators; acting via microvascular permeability-increasing mechanisms that can, depending on dose of agonist and purine receptor under study, involve the tachykinin NK1 receptor and mast cell amines.

Inhibition of mechanical activation of guinea-pig airway afferent neurons by amiloride analogues

1. The aim of this study was to investigate a role for Epithelial Sodium Channels (ENaCs) in the mechanical activation of low-threshold vagal afferent nerve terminals in the guinea-pig trachea/bronchus. 2. Using extracellular single-unit recording techniques, we found that the ENaC blocker amiloride, and its analogues dimethylamiloride and benzamil caused a reduction in the mechanical activation of guinea-pig airway afferent fibres. 3. Amiloride and it analogues also reduced the sensitivity of afferent fibres to electrical stimulation such that greater stimulation voltages were required to induce action potentials from their peripheral terminals within the trachea/bronchus. 4. The relative potencies of these compounds for inhibiting electrical excitability of afferent nerves were similar to that observed for inhibition of mechanical stimulation (dimethylamiloride approximately benzamil > amiloride). This rank order of potency is incompatible with the known rank order of potency for blockade of ENaCs (benzamil > amiloride >> dimethylamiloride). 5. As voltage-gated sodium channels play an important role in determining the electrical excitability of neurons, we used whole-cell patch recordings of nodose neuron cell bodies to investigate the possibility that amiloride analogues caused blockade of these channels. At the concentration required to inhibit mechanical activation of vagal nodose afferent fibres (100 microM), benzamil caused significant inhibition of voltage-gated sodium currents in neuronal cell bodies acutely isolated from guinea-pig nodose ganglia. 6. Combined, our findings suggest that amiloride and its analogues did not selectively block mechanotransduction in airway afferent neurons, but rather they reduced neuronal excitability, possibly by inhibiting voltage-gated sodium currents.

Agonists of proteinase-activated receptor 1 induce plasma extravasation by a neurogenic mechanism

Thrombin, generated in the circulation during injury, cleaves proteinase-activated receptor 1 (PAR1) to stimulate plasma extravasation and granulocyte infiltration. However, the mechanism of thrombin-induced inflammation in intact tissues is unknown. We hypothesized that thrombin cleaves PAR1 on sensory nerves to release substance P (SP), which interacts with the neurokinin 1 receptor (NK1R) on endothelial cells to cause plasma extravasation. PAR1 was detected in small diameter neurons known to contain SP in rat dorsal root ganglia by immunohistochemistry and in situ hybridization. Thrombin and the PAR1 agonist TFLLR-NH(2) (TF-NH(2)) increased [Ca(2+)](i) >50% of cultured neurons (EC(50)s 24 mu ml(-1) and 1.9 microM, respectively), assessed using Fura-2 AM. The PAR1 agonist completely desensitized responses to thrombin, indicating that thrombin stimulates neurons through PAR1. Injection of TF-NH(2) into the rat paw stimulated a marked and sustained oedema. An NK1R antagonist and ablation of sensory nerves with capsaicin inhibited oedema by 44% at 1 h and completely by 5 h. In wild-type but not PAR1(-/-) mice, TF-NH(2) stimulated Evans blue extravasation in the bladder, oesophagus, stomach, intestine and pancreas by 2 - 8 fold. Extravasation in the bladder, oesophagus and stomach was abolished by an NK1R antagonist. Thus, thrombin cleaves PAR1 on primary spinal afferent neurons to release SP, which activates the NK1R on endothelial cells to stimulate gap formation, extravasation of plasma proteins, and oedema. In intact tissues, neurogenic mechanisms are predominantly responsible for PAR1-induced oedema.

The endogenous cannabinoid agonist, anandamide stimulates sensory nerves in guinea-pig airways

The endogenous cannabinoid agonist, anandamide produced a modest contractile response in guinea-pig isolated bronchus compared with the vanilloid receptor agonist capsaicin. The contractile response to both anandamide and capsaicin was inhibited by the vanilloid receptor antagonist, capsazepine. Furthermore, the NK(2)-selective antagonist, SR48968 but not the NK(1)-selective antagonist, SR140333 inhibited contractile responses to anandamide. The contractile response to anandamide was abolished in tissues desensitized by capsaicin. However, anandamide failed to cross-desensitize the contractile response to capsaicin. The contractile response to anandamide was not significantly altered in the presence of the CB(1) receptor antagonist, SR141716A, nor the amidase inhibitor, phenylmethylsulphonyl fluoride (PMSF) but was significantly increased in the presence of the neutral endopeptidase inhibitor, thiorphan. The cannabinoid agonist, CP55,940 failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) response in guinea-pig airways. In contrast, the ORL(1) receptor agonist, nociceptin, significantly inhibited this response. The results demonstrate that anandamide induces a modest contractile response in guinea-pig isolated bronchus that is dependent upon the activation of vanilloid receptors on airway sensory nerves. However, cannabinoid receptors do not appear to play a role in this regard, nor in regulating the release of neuropeptides from airway sensory nerves under physiological conditions.

Anandamide activates peripheral nociceptors in normal and arthritic rat knee joints

The effects of the endogenous cannabinoid anandamide were studied on peripheral, polymodal nociceptors recorded from normal and chronically inflamed (Freund's adjuvant) knee joint afferents in rats anaesthetized with pentobarbitone. Anandamide (860 nmol) caused a rapid, short lasting excitation of a sub-population of capsaicin-sensitive nociceptive afferents in normal knee joints (7.2+/-2.3 impulses s(-1); n=15 units from five animals). In arthritic joints there were 9.7+/-3.0 impulses s(-1) (n=11 from six animals), which was not significantly different from normal joints. The excitation was dose dependent (8.6 - 2900 nmol) and mediated by activation of the vanilloid receptor (VR(1)) as it was abolished by the VR1 antagonist capsazepine (1 mg kg(-1)). Our results show that anandamide, at high doses, can activate nociceptive afferents innervating the rat knee joints, in contrast with its widely described analgesic actions.

Substance P mediates inflammatory oedema in acute pancreatitis via activation of the neurokinin-1 receptor in rats and mice

Pancreatic oedema occurs early in the development of acute pancreatitis, and the overall extent of fluid loss correlates with disease severity. The tachykinin substance P (SP) is released from sensory nerves, binds to the neurokinin-1 receptor (NK1-R) on endothelial cells and induces plasma extravasation, oedema, and neutrophil infiltration, a process termed neurogenic inflammation. We sought to determine the importance of neurogenic mechanisms in acute pancreatitis. Pancreatic plasma extravasation was measured using the intravascular tracers Evans blue and Monastral blue after administration of specific NK1-R agonists/antagonists in rats and NK1-R(+/+)/(-/-) mice. The effects of NK1-R genetic deletion/antagonism on pancreatic plasma extravasation, amylase, myeloperoxidase (MPO), and histology in cerulein-induced pancreatitis were characterized. In rats, both SP and the NK1-R selective agonist [Sar(9) Met(O(2))(11)]SP stimulated pancreatic plasma extravasation, and this response was blocked by the NK1-R antagonist CP 96,345. Selective agonists of the NK-2 or NK-3 receptors had no effect. In rats, cerulein stimulated pancreatic plasma extravasation and serum amylase. These responses were blocked by the NK1-R antagonist CP 96,345. In wildtype mice, SP induced plasma extravasation while SP had no effect in NK1-R knockout mice. In NK1-R knockout mice, the effects of cerulein on pancreatic plasma extravasation and hyperamylasemia were reduced by 60%, and pancreatic MPO by 75%, as compared to wildtype animals. Neurogenic mechanisms of inflammation are important in the development of inflammatory oedema in acute interstitial pancreatitis.

Naloxone blocks endomorphin-1 but not endomorphin-2 induced inhibition of tachykinergic contractions of guinea-pig isolated bronchus

The recently identified endogenous agonists on the mu-opioid-receptor (mu OR), endomorphin-1 (EM-1) and endomorphin-2 (EM-2), induce a concentration dependent inhibition of electrical field stimulation (EFS)-induced tachykinin-mediated contractions of the guinea-pig bronchus (ED50s < 10 nM for both compounds). Surprisingly, only endomorphin-1 effects could be blocked by naloxone (10 microM), whereas endomorphin-2 effects were not affected by specific antagonists for the mu-, kappa-, and delta-opioid-receptor.

Interaction of amylin with calcitonin gene-related peptide receptors in the microvasculature of the hamster cheek pouch in vivo

1. This study used intravital microscopy to investigate the receptors stimulated by amylin which shares around 50% sequence homology with the vasodilator calcitonin gene-related peptide (CGRP) in the hamster cheek pouch microvasculature in vivo. 2. Receptor agonists dilated arterioles (diameters 20-40 microm). The -log of the concentrations (+/- s.e.mean; n = 8) causing 50% increase in arteriole diameter were: human betaCGRP (10.8 +/- 0.3), human alphaCGRP (10.8 +/- 0.4), rat alphaCGRP (10.4 +/- 0.3). Rat amylin and the CGRP2 receptor selective agonist [Cys(ACM2,7]-human alphaCGRP were 100 fold less potent (estimates were 8.5 +/- 0.4 and 8.2 +/- 0.3 respectively). 3. The GCRP1 receptor antagonist, CGRP8-37 (300 nmol kg(-1); i.v.) reversibly inhibited the increase in diameter evoked by human alphaCGRP (0.3 nM) from 178 +/- 22% to 59 +/- 12% (n = 8; P < 0.05) and by rat amylin (100 nM) from 138 +/- 23% to 68 +/- 24% (n = 6; P < 0.05). CGRP8-37 did not inhibit vasodilation evoked by substance P (10 nM; n = 4: P > 0.05). 4. The amylin receptor antagonist, amylin8-37 (300 nmol kg(-1); i.v.) did not significantly inhibit the increase in diameter evoked by human alphaCGRP (0.3 nM) which was 112 +/- 26% in the absence, and 90 +/- 29% in the presence of antagonist (n = 4; P < 0.05); nor that evoked by rat amylin (100 nM) which was 146 +/- 23% in the absence and 144 +/- 32% in the presence of antagonist (n = 4; P > 0.05). 5. The agonist profile for vasodilatation and the inhibition of this dilatation by CGRP8-37, although not the amylin8-37 indicates that amylin causes vasodilatation through interaction with CGRP1 receptors in the hamster cheek pouch.

Stimulation of airway sensory nerves by cyclosporin A and FK506 in guinea-pig isolated bronchus

We have investigated the contractile property of cyclosporin A and FK506 in guinea-pig isolated bronchus. Cyclosporin A (10 microM) failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) and cholinergic contractile response (per cent methacholine Emax) induced by electrical field stimulation (EFS). In contrast, eNANC responses were significantly attenuated by both the neurokinin (NK)-1 and (NK)-2 receptor antagonists, N-acetyl-L-tryptophan 3,5-bis (trifluoromethyl)-benzyl and SR48968, respectively. Cyclosporin A and FK506 caused a concentration-dependent contraction in guinea-pig isolated bronchus, which was significantly attenuated by NK-1 and NK-2 receptor antagonists. The capsaicin receptor antagonist, capsazepine (10 microM) significantly reduced the contractile response to cyclosporin A and capsaicin, but not to FK506. The N-type calcium channel blocker, omega-Conotoxin (omegaCTX: 10 nM), significantly reduced the contractile response to FK506 and the eNANC response following EFS. In contrast, omega-CTX failed to significantly reduce the contractile potency to capsaicin or cyclosporin A. In bronchial preparations desensitized by repeated application of capsaicin (1 microM), the contractile responses to both cyclosporin A (100 microM) and FK506 (100 microM), were significantly reduced. In contrast, the contractile responses to substance P and neurokinin A (10 microM) were not altered. Furthermore, repeated application of cyclosporin A (100 microM) significantly inhibited the contractile response to capsaicin (1 microM). The findings from this study would indicate that cyclosporin A and FK506 mediate contraction of guinea-pig isolated bronchus secondary to the release of neuropeptides from airway sensory nerves. However, the release of sensory neuropeptides appears to be mediated via different mechanisms for cyclosporin A and FK506, the former by stimulation of the vanilloid receptor and the latter via opening of N-type calcium channels.

Stretch-evoked inhibition of spontaneous migrating contractions in a whole mount preparation of the guinea-pig upper urinary tract

1. The effects of circumferentially-applied stretch on the spontaneous contractility of a whole mount preparation of the guinea-pig upper urinary tract (UUT) (renal pelvis and ureter) were investigated by use of standard isometric tension recording techniques. 2. Simultaneous tension recordings of the proximal and distal portions of the renal pelvis (RP) and ureter revealed that spontaneous contractions, in 79% (n = 66) of preparations, originated in the proximal RP (at a frequency of 4.5 min(-1)) and propagated to the distal RP and ureter at a velocity of 1-3 cm s(-1). Pretreatment with tetrodotoxin (TTX) (3-10 microM) or N(G)-nitro-L-arginine (100 microM) had little effect on the spontaneous contractility of the UUT, motility indexes (MIs) (contraction amplitude x contraction frequency) calculated after 20 min exposure were little affected by TTX or N(G)-nitro-L-arginine (L-NOARG). Omega-conotoxin GVIA (100 nM) significantly reduced MI values in both the proximal RP and ureter. 3. Exposure of the spontaneously-active UUT to capsaicin (10 microM for 15 min) induced a transient increase in UUT contractility, followed by a prolonged negative inotropic effect. The MI values, calculated 60 min after the washout of capsaicin, for the proximal and distal RP and ureter were reduced to 56%, 53% (n = 18) and 61% (n = 16), respectively, of their control values. This capsaicin pretreatment blocked the positive inotropic effects of transmural electrical nerve stimulation on UUT contractility to reveal a small inhibitory effect which was readily blocked by tetrodotoxin (3 microM) (n = 3). The excitatory and inhibitory actions of nerve stimulation were both blocked by TTX (3 microM). 4. A second exposure to capsaicin (10 microM for 15 min), further reduced the MI values (calculated 60 min after washout) in the proximal and distal RP to 41% and 31%, respectively (n = 6; P<0.05), of the initial control values. 5. In 61% (n = 99) of preparations, the application of stretch to the proximal RP (0.5 to 2 mm) evoked a decrease in the amplitude of the contractions recorded in the distal RP, but not in the ureter. Stretch applied to the distal RP or ureter had no effect on the contractions recorded in the other regions of the UUT. 6. In 5 out of 6 preparations, a single application of capsaicin (10 microM for 15 min) had little effect on the change in contractile force of the distal RP evoked upon stretch of the proximal RP. 7. The inhibition of the distal RP upon stretch of the proximal RP was partially reduced (P<0.05) when the UUT was pretreated with the calcitonin gene-related peptide (CGRP) receptor antagonist, hCGRP (8-37) (1 microM). 8. The application of the CGRP receptor agonist, hCGRP (100 nM) inhibited contractility in the UUT in a region dependent manner. The MI of the proximal RP was decreased 32% after 6 min; while the MIs of the distal RP and ureter were reduced 83% and 63%, respectively, within 5 min of the application of hCGRP. 9. Glibenclamide (1 microM) had little effect on the spontaneous contractility of the UUT, but significantly reduced the inhibition of the distal RP evoked upon stretch (0.5 to 2 mm) of the proximal RP. TTX (3-10 microM), L-NOARG (100 microM) or omega-conotoxin GVIA (100 nM) had little effect on the stretch-evoked inhibition of the distal RP. 10. It was concluded that circumferential stretch of the proximal RP inhibits the contractility of the distal RP and that a component of this inhibition involves the activation of a glibenclamide-sensitive mechanism via the release of endogenous CGRP, possibly from the varicosities of intramural sensory nerves.

CGRP and nitric oxide of neuronal origin and their involvement in neurogenic vasodilatation in rat skin microvasculature

1. Sensory nerves are important for the initiation of neurogenic inflammation and tissue repair. Both calcitonin gene-related peptide (CGRP) and nitric oxide (NO) have been implicated in neurogenic vasodilatation and inflammatory responses. 2. A blister model in the rat hind footpad was used as a site to induce neurogenic vasodilatation in response to antidromic electrical stimulation of the sciatic nerve. Blood flux was monitored with a laser Doppler flow monitor. 3. The quantitative contributions of CGRP and NO to vasodilatation were examined by use of the CGRP receptor antagonist CGRP8-37 and NO synthase inhibitors 7-nitroindazole (7-NI), 3-bromo 7-NI and N(G)-nitro L-arginine methyl ester (L-NAME). The potential modulatory role of endothelin was examined by use of the ET(A) receptor antagonist BQ-123. 4. CGRP8-37 (10 microM) was perfused over the blister base before nerve stimulation and continuously throughout the post-stimulation period, resulting in a significant reduction (41%) in the blood flux vascular response. 5. Pretreatment with the specific neuronal NO synthase inhibitors, 7-NI and 3-bromo 7-NI (10 mg kg(-1), i.v.), and of the non-specific L-NAME (100 microM), resulted in significant inhibition of the blood flux response (36%, 72% and 57% decrease, respectively). In contrast, 7-NI treatment in young rats pretreated with capsaicin had no further effect on the vascular response, suggesting that the source of NO is the sensory nerves. 6. BQ-123 (10 microM) significantly enhanced the stimulation-induced blood flux response (61% increase). When 7-NI was co-administered with either CGRP8-37 or BQ-123, the drug actions were additive, suggesting that there was no interaction between NO and CGRP or endothelin. 7. These data suggest that both NO and CGRP participate in neurogenic vasodilatation in rat skin microvasculature and that this response is modulated by endogenous endothelin.

Does low power laser light used in laser Doppler systems affect the sensory nerves?

BACKGROUND/AIMS

Many subjects have stated that they can sense the laser light during cutaneous laser Doppler recordings. The aim of the study was therefore to investigate if low power laser light used in laser Doppler systems affects the sensory nerves.

METHODS

Single point recording as well as imaging was performed with the laser Doppler perfusion imager at the finger pulp, dorsal and ventral side of the hand and the forearm skin in 12 healthy volunteers. The hypothesis "the subject can not sense the laser beam" was tested by double blind random control of the on-off pattern of the laser light reaching the skin. In total, 96 trials (each including 12 recordings) were performed. Furthermore, it was investigated if the blood flow level was influenced by the subjects "sense" of being measured.

RESULTS

The hypothesis was rejected in 92 out of 96 trials. Three of the trials that could not be rejected were recorded from the same subject. In further trials no reproducibility was found. The blood flow level was not influenced by the subjects "sense" of being measured.

CONCLUSIONS

In general, the laser light used in laser Doppler imaging systems does not influence the sensory nerves. However, it can not be excluded that the laser light used in laser Soppier perfusion imaging (LDPI) affects sensory nerves under unknown circumstances and at specific spots in cutaneous tissue.

The effect of okadaic acid on non-adrenergic non-cholinergic contraction in guinea-pig isolated bronchus

1. We have investigated the role of phosphatases in modulating contractile responses to electrical field stimulation (EFS), methacholine, substance P and capsaicin in guinea-pig isolated main bronchus by use of the phosphatase 1 and 2A inhibitor okadaic acid. 2. Non-adrenergic non-cholinergic (eNANC) contractile responses were elicited by EFS (3 Hz, 20 s, 0.5 ms max. voltage) in the guinea-pig isolated main bronchus in the presence of the non-selective muscarinic antagonist, atropine (1 microM), the non-selective beta-adrenoceptor antagonist; propranolol (1 microM), the neutral endopeptidase inhibitor thiorphan (10 microM) and the cyclo-oxygenase inhibitor, indomethacin (5 microM). Okadaic acid significantly attenuated eNANC contractile responses (% inhibition) elicited by EFS (0.01 microM, 15.2 +/- 26.9%; 0.03 microM, 30.4 +/- 13.9%; 0.01 microM, 39.8 +/- 5.1%; 0.3 microM, 59.5 +/- 8.7%; 1 microM 77.8 +/- 7.8%; P < 0.05, n = 4). In contrast, the inactive analogue 1-Nor okadaone (0.3 microM) failed to attenuate significantly eNANC contractile responses (% inhibition elicited by 1-Nor okadaone, -1.25 +/- 8.5% vs dimethylsulphoxide (DMSO), -13.5 +/- 21.5%; P > 0.05, n = 4). 3. Cholinergic contractile responses were elicited by EFS (1-30 Hz, 10 s, 0.5 ms max. voltage) in guinea-pig isolated bronchus in the presence of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 30 microM). Okadaic acid failed to attenuate significantly the contractile (% methacholine Emax) response elicited by EFS at all frequencies tested compared with the control (1 Hz, control, 22 +/- 7.9% vs okadaic acid, 18 +/- 7.7%; 3 Hz, control, 26 +/- 6.9% vs okadaic acid, 27 +/- 9.1%; 10 Hz, control, 36 +/- 7.6% vs okadaic acid, 33 +/- 8.9%; 30 Hz, control, 50 +/- 7.6% vs okadaic acid, 42 +/- 14%; P > 0.05, n = 4). 4. Okadaic acid (0.3 microM) failed to alter significantly the contractile potency (pD2) to capsaicin (okadaic acid, 9.0 +/- 0.5, vs DMSO, 9.2 +/- 0.4; P > 0.05 n = 6), substance P (okadaic acid, 7.6 +/- 0.3 vs DMSO, 8.2 +/- 0.2; P > 0.05 n = 7) or methacholine (okadaic acid, 6.4 +/- 0.2 vs DMSO, 6.4 +/- 0.3; P > 0.05 n = 4). 5. Okadaic acid (0.01-1 microM) did not appear to reverse substance P-induced tone. The maximal relaxant response (% reversal of substance P-induced tone) mediated by okadaic acid (1 microM) was 33 +/- 11.7% (n = 4), this was not significantly different from the DMSO (0.8%) or a time-dependent fall in tone of 34.3 +/- 23.1% (n = 4) and 33 +/- 15.8% (n = 4), respectively. Okadaic acid (0.3 microM) failed to augment isoprenaline-induced relaxation responses in substance P contracted bronchus (okadaic acid, 6.5 +/- 0.4 vs DMSO, 5.9 +/- 0.3; P > 0.05, n = 9). 6. These results indicate that protein phosphatases appear to regulate the release of sensory neuropeptides from airway sensory nerves in response to electrical field stimulation.

Involvement of cytokines in lipopolysaccharide-induced facilitation of CGRP release from capsaicin-sensitive nerves in the trachea: studies with interleukin-1beta and tumor necrosis factor-alpha

Lipopolysaccharide (LPS), an endotoxin, produces pain behavior, inflammation, and changes in immune function. Many of these effects are secondary to the production of cytokines. In the present study, we investigated the effect of LPS on the releasing function of afferent terminals as measured by calcitonin gene-related peptide (CGRP) release in ex vivo perfused rat trachea, and examined the possible role of the cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) as intermediaries in this effect. Systemic injection of LPS (0.75 mg/kg, i.p.) in adult rats induced an increase in body temperature followed by hypothermia, indicating ongoing infection. We observed that capsaicin-induced (0.1 microM) tracheal CGRP release was significantly enhanced in the LPS-treated animals after 5 hr. This enhancement of the peptide release by LPS was blocked by IL-1beta tripeptide antagonist Lys-D-Pro-Thr (10 microM) and mimicked by IL-1beta and TNF-alpha (10-100 pg/ml), suggesting that the potentiating effect of LPS on CGRP release is mediated by generation of IL-1beta and TNF-alpha. IL-1beta-induced augmentation of CGRP release was blocked by Lys-D-Pro-Thr. Additionally, the cyclooxygenase inhibitor ketorolac (10 microM) significantly attenuated the facilitatory effects of LPS and IL-1b, indicating involvement of prostanoids. These findings suggest that endotoxin treatment generated cytokines such as IL-1b and TNF-alpha that regulated the peripheral releasing function of primary sensory afferents by sensitizing the terminals and facilitating peptide release. This effect is prostanoid dependent.