The effects of bradykinin and prostaglandin E1 on rat cutaneous afferent nerve activity.

1 The activity produced by intra-arterial bradykinin and prostaglandin E1 was investigated in multifibre strands dissected from the saphenous nerves of anaesthetized rats. 2 Bradykinin (0.5-10mug) alone produced little activity in nerve strands but produced considerable activity following a 10 min infusion, but not a single injection, of prostaglandin E1 (5-100 ng). 3 Prostaglandin E, alone produced a few large height spikes but following several injections of bradykinin smaller height spikes were also produced by prostaglandin E1. 4 It was concluded that the presence of a low concentration of prostaglandin E, is required for bradykinin to manifest its actions and that bradykinin and prostaglandin E1 are mutually potentiating in their effects on afferent nerve terminals.     

Central and peripheral effects of bradykinin and prostaglandin E2 on blood pressure in conscious rats

Summary Bradykinin or prostaglandin E2 (PGE2), when injected intravenously, decreased blood pressure of conscious rats in a dose-dependent manner, while intracerebroventricular injections of bradykinin or PGE2 caused a dose-dependent increase in blood pressure. SQ 14,225, an inhibitor of angiotensin converting enzyme, potentiated the central pressor or peripheral depressor effect of bradykinin. Indomethacin, an inhibitor of prostaglandin synthesis, almost completely inhibited the central pressor effect of bradykinin when injected intraventricularly. Indomenthacin, when injected intravenously, failed to inhibit the peripheral depressor effect of bradykinin, whereas it significantly attenuated the peripheral depressor effect of bradykinin when the angiotensin converting enzyme was inhibited with SQ14,225. These results suggest that the central pressor effect of bradykinin is mainly mediated by the synthesis of prostaglandins in the central nervous system, while only a small fraction of peripheral depressor effect of bradykinin is, at least in conscious rats, mediated by the synthesis of prostaglandins in the systemic circulation.     

The effects of prostaglandin E1, bradykinin and histamine on canine synovial vascular permeability.

1 The relative effects of prostaglandin E1, bradykinin and histamine on canine synovial vascular permeability were investigated by a method based on the measurement of the amounts of radiolabelled dextran (molecular weight 20,000) leaking from the circulation into the synovial cavity. 2 Bradykinin, prostaglandin E1 and histamine in that order of potency all increased synovial vascular permeability. Threshold concentrations were 0.3 micrometer, 3 micrometer and 30 micrometer respectively. 3 The effects of infusion of prostaglandin E1 combined with either bradykinin or histamine were greater than mere summation.     

Neuropeptide Y, Y1, Y2 and Y4 receptors mediate Y agonist responses in isolated human colon mucosa

1. The aim of this study was to provide a pharmacological characterization of the Y receptor types responsible for neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) effects upon electrogenic ion transport in isolated human colonic mucosa. 2. Preparations of descending colon were voltage-clamped at 0 mV in Ussing chambers and changes in short-circuit current (I(sc)) continuously recorded. Basolateral PYY, NPY, human PP (hPP), PYY(3 - 36), [Leu(31), Pro(34)]PYY (Pro(34)PYY) and [Leu(31), Pro(34)]-NPY (Pro(34)NPY) all reduced basal I(sc) in untreated colon. Of all the Y agonists tested PYY(3 - 36) responses were most sensitive to tetrodotoxin (TTX) pretreatment, indicating that Y(2)-receptors are located on intrinsic neurones as well as epithelia in this tissue. 3. The EC(50) values for Pro(34)PYY, PYY(3 - 36) and hPP were 9.7 nM (4.0 - 23.5), 11.4 nM (7.6 - 17.0) and 14.5 nM (10.2 - 20.5) and response curves exhibited similar efficacies. The novel Y(5) agonist [Ala(31), Aib(32)]-NPY had no effect at 100 nM. 4. Y(1) receptor antagonists, BIBP3226 and BIBO3304 both increased basal I(sc) levels per se and inhibited subsequent PYY and Pro(34)PYY but not hPP or PYY(3 - 36) responses. The Y(2) antagonist, BIIE0246 also raised basal I(sc) levels and attenuated subsequent PYY(3 - 36) but not Pro(34)PYY or hPP responses. 5. We conclude that Y(1) and Y(2) receptor-mediated inhibitory tone exists in human colon mucosa. PYY and NPY exert their effects via both Y(1) and Y(2) receptors, but the insensitivity of hPP responses to either Y(1) or Y(2) antagonism, or to TTX, indicates that Y(4) receptors are involved and that they are predominantly post-junctional in human colon.     

Microsomal prostaglandin E synthase-1 contributes to ischaemic excitotoxicity through prostaglandin E2 EP3 receptors

Background and purpose:

Although microsomal prostaglandin E synthase (mPGES)-1 is known to contribute to stroke injury, the underlying mechanisms remain poorly understood. This study examines the hypothesis that EP₃ receptors contribute to stroke injury as downstream effectors of mPGES-1 neurotoxicity through Rho kinase activation.

Experimental approach:

We used a glutamate-induced excitotoxicity model in cultured rat and mouse hippocampal slices and a mouse middle cerebral artery occlusion–reperfusion model. Effects of an EP₃ receptor antagonist on neuronal damage in mPGES-1 knockout (KO) mice was compared with that in wild-type (WT) mice.

Key results:

In cultures of rat hippocampal slices, the mRNAs of EP_1–4 receptors were constitutively expressed and only the EP₃ receptor antagonist ONO-AE3-240 attenuated and only the EP₃ receptor agonist ONO-AE-248 augmented glutamate-induced excitotoxicity in CA1 neurons. Hippocampal slices from mPGES-1 KO mice showed less excitotoxicity than those from WT mice and the EP₃ receptor antagonist did not attenuate the excitotoxicity. In transient focal ischaemia models, injection (i.p.) of an EP₃ antagonist reduced infarction, oedema and neurological dysfunction in WT mice, but not in mPGES-1 KO mice, which showed less injury than WT mice. EP₃ receptor agonist-induced augmentation of excitotoxicity in vitro was ameliorated by the Rho kinase inhibitor Y-27632 and Pertussis toxin. The Rho kinase inhibitor HA-1077 also ameliorated stroke injury in vivo.

Conclusion and implications:

Activity of mPGES-1 exacerbated stroke injury through EP₃ receptors and activation of Rho kinase and/or G_i. Thus, mPGES-1 and EP₃ receptors may be valuable therapeutic targets for treatment of human stroke.This article is commented on by Andreasson, pp. 844–846 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2010.00715.x     

The effects of sensory denervation on the responses of the rabbit eye to prostaglandin E1, bradykinin and substance P.

1 Six to eight days after diathermic destruction of the fifth cranial nerve in the rabbit, the ocular hypertensive and miotic responses to intracameral administration of capsaicin, bradykinin, and prostaglandin E1 were greatly reduced or completely abolished. The response to substance P was not abolished. 2 A response could still be obtained to chemical irritants 36 h after coagulation of the nerve and it is deduced that manifestation of the response is dependent upon functional sensory nerve terminals, and is independent of central connections. 3 It is suggested that prostaglandin E1 and bradykinin act directly upon the sensory nerve endings and that propagation of the response is augmented by axon reflex. 4 In view of the ability of substance P to induce miosis in the denervated eyes, it is presumed that its actions are not mediated via sensory nerves. 5 It is considered possible that the mediator(s) released from sensory nerve endings after chemical irritation or antidromic stimulation may act in the same way as substance P with regard to the miotic effect. 6 Synthetic substance P will only produce ocular hypertension in doses which induce a maximal miotic response. This may either be a question of access or a partial resemblance to the endogenous mediator.     

Neuropeptide Y1- and Y2-receptor-mediated cardiovascular effects in the anesthetized guinea pig, rat, and rabbit

Neuropeptide Y (NPY) causes vasoconstriction through Y1-receptors and inhibits vagal bradycardia through presynaptic Y2-receptors. These effects of NPY were investigated in anesthetized guinea pigs, rats, and rabbits to find the most suitable species for evaluation of Y1- and Y2-active agents in vivo. The increase in blood pressure (through Y1) of lower doses of NPY was similar in the three species (ED50, 0.9 +/- 0.13, 0.8 +/- 0.39, and 0.6 +/- 0.09 nmol/kg, respectively), but higher doses had depressor effects in four of six rats. Vagal bradycardia, induced by electrical stimulation of the right cervical vagus nerve, was inhibited by NPY in the guinea pig and in the rat (ED35, 3.5 +/- 0.46 and 11.2 +/- 1.79 nmol/kg, respectively; p < 0.05) but not in the rabbit. In the guinea pig, the Y2-receptor-preferring fragment NPY(3-36) and the selective Y1-receptor antagonist H 409/22 were used to confirm that the increase in blood pressure was mediated solely through the Y1-receptor and the vagal inhibition solely through the Y2-receptor. Aside from the cardiovascular effects, NPY caused a decrease in the body temperature and inhibited vagal bronchoconstriction in this species. Considering that NPY may cause depressor effects in the rat and has no effect on the vagal bradycardia in the rabbit, the guinea pig is preferable to both these species for assessment of Y1- and Y2-receptor-active agents in vivo.     

Central Neuropeptide Y Modulates Binge-Like Ethanol Drinking in C57BL/6J Mice via Y1 and Y2 Receptors

Frequent binge drinking has been linked to heart disease, high blood pressure, type 2 diabetes, and the development of ethanol dependence. Thus, identifying pharmaceutical targets to treat binge drinking is of paramount importance. Here we employed a mouse model of binge-like ethanol drinking to study the role of neuropeptide Y (NPY). To this end, the present set of studies utilized pharmacological manipulation of NPY signaling, immunoreactivity (IR) mapping of NPY and NPY receptors, and electrophysiological recordings from slice preparations of the amygdala. The results indicated that central infusion of NPY, a NPY Y1 receptor (Y1R) agonist, and a Y2R antagonist significantly blunted binge-like ethanol drinking in C57BL/6J mice (that achieved blood ethanol levels >80 mg/dl in control conditions). Binge-like ethanol drinking reduced NPY and Y1R IR in the central nucleus of the amygdala (CeA), and 24 h of ethanol abstinence after a history of binge-like drinking promoted increases of Y1R and Y2R IR. Electrophysiological recordings of slice preparations from the CeA showed that binge-like ethanol drinking augmented the ability of NPY to inhibit GABAergic transmission. Thus, binge-like ethanol drinking in C57BL/6J mice promoted alterations of NPY signaling in the CeA, and administration of exogenous NPY compounds protected against binge-like drinking. The current data suggest that Y1R agonists and Y2R antagonists may be useful for curbing and/or preventing binge drinking, protecting vulnerable individuals from progressing to the point of ethanol dependence.     

Neuropeptide Y2 receptors as drug targets for the central regulation of body weight

During the past decade, a detailed understanding has emerged of the aminergic and peptidergic neural pathways present within the brain that regulate appetite. Central among the peptide regulators is neuropeptide Y (NPY), a potent orexigenic agent that acts through five different receptor subtypes. Efforts to find novel appetite suppressant drugs that inhibit the interaction of NPY with either the NPY Y1 or NPY Y5 receptor subtypes have proven disappointing. Attempts have now been made to identify an NPY Y2 stimulator that will suppress appetite. Within the hypothalamus, NPY Y2 receptors have a predominantly presynaptic location where they act to inhibit NPY release. Stimulation of NPY Y2 receptors with synthetic peptide ligands or the gut derived peptide PY3-36 has been shown to reduce food intake. The NPY Y2 receptor has a wide distribution both within the brain and in the periphery. Stimulation of the NPY Y2 subtype at these sites produces a wide array of effects unrelated to changes in food intake. In consequence, the administration of both endogenous and exogenous agonists of the NPY Y2 receptor is likely to cause side effects, particularly regarding pituitary hormone release, as well as on the cardiovascular and gastrointestinal systems. The possibility that long-term NPY Y2 agonism could cause bone thinning and retinal angiogenesis are of particular concern and will need to be investigated as drug discovery moves forward.     

Neuropeptide Y potentiates via Y2-receptors the inhibitory effect of noradrenaline in rat locus coeruleus neurones

Summary Intracellular recordings were carried out in a pontine slice preparation of the rat brain containing the locus coeruleus (LC). Pressure application of noradrenaline with various pulse durations inhibited the spontaneous frequency of action potentials and hyperpolarized the membrane. Neuropeptide Y (NPY), its C-terminal fragment NPY(16–36) and peptide YY (PYY), at a concentration of 0.1 µmol/l all, potentiated the effect of noradrenaline, while [Leu³¹, Pro³⁴]NPY (0.1 µmol/l) was inactive. These results are compatible with the presence of Y₂-type NPY-receptors at the cell somata of LC neurones. Correspondence to: P. Illes at the above address     

Heme oxygenase-1 induction modulates microsomal prostaglandin E synthase-1 expression and prostaglandin E2 production in osteoarthritic chondrocytes

Pro-inflammatory cytokines such as interleukin-1β (IL-1β) may participate in the pathogenesis of cartilage damage in osteoarthritis (OA) through the production of catabolic enzymes and inflammatory mediators. Induction of heme oxygenase-1 (HO-1) has previously been shown to exert anti-inflammatory effects in different cell types. We have investigated whether HO-1 induction may modify chondrocyte viability and the production of relevant mediators such as oxidative stress and prostaglandin E₂ (PGE₂) elicited by IL-1β in OA chondrocytes. Chondrocytes were isolated from OA cartilage and used in primary culture. Cells were stimulated with IL-1β in the absence or presence of the HO-1 inducer cobalt protoporphyrin IX (CoPP). Gene expression was assessed by quantitative real-time PCR, protein levels by ELISA and Western blot, apoptosis by laser scanning cytometry using annexin V-FITC and TUNEL assays, and oxidative stress by LSC with dihydrorhodamine 123. HO-1 induction by CoPP enhanced chondrocyte viability and aggrecan content while inhibiting apoptosis and oxidative stress generation. PGE₂ is produced in OA chondrocytes stimulated by IL-1β by the coordinated induction of cyclooxygenase-2 and microsomal PGE synthase 1 (mPGES-1). The production of PGE₂ was decreased by HO-1 induction as a result of diminished mPGES-1 protein and mRNA expression. Transfection with HO-1 small interfering RNA counteracted CoPP effects. In addition, the activation of nuclear factor-κB and early growth response-1 was significantly reduced by CoPP providing a basis for its anti-inflammatory effects. These results confirm the protective role of HO-1 induction in OA chondrocytes and suggest the potential interest of this strategy in degenerative joint diseases.     

The effects of intra-arterial bradykinin, histamine, acetylcholine and prostaglandin E1 on nociceptive and non-nociceptive dorsal horn neurones of the cat.

The effects of peripherally administered algesic agents were investigated on the firing of cat dorsal horn interneurones classified as nociceptive or non-nociceptive according to the peripheral stimuli that excited them. A small amount of bradykinin injected into the blood supplying the receptive fields of cells was a potent specific stimulus causing activation of nociceptive cells and slowly conducting nerve fibres. Larger amounts of bradykinin and large amounts of histamine, 5-hydroxytryptamine and acetylcholine activated both nociceptive and non-nociceptive cells. Prostaglandin E1 enhanced the effects of bradykinin and histamine on nociceptive cells. Prostaglandin E1 also increased the response of these cells to the application of noxious heat whilst aspirin reduced this response. These results support a chemosensitive theory of nociceptor activation and show bradykinin to be the most potent and specific of the suggested endogenous algesic agents in causing activation of CNS nociceptive pathways.     

Inhibitory effects of prostaglandin E1 and E2 on cholinergic transmission in isolated canine tracheal muscle.

The contractile response of the isolated canine tracheal muscle to the transmural nerve stimulation was depressed by atropine and augmented by physostigmine, indicating that the response was predominantly mediated via the parasympathetic nerve. The contractile response to the transmural nerve stimulation was inhibited by prostaglandin E1 (PGE1) and E2 (PGE2) (10(-7) to 10(-5) g/ml) and the inhibitory action of PGE1 was more potent than that of PGE2. On the other hand, the contractile response of the tracheal muscle to exogenously administered ACh was unaffected by 10(-6) g/ml of PGE1 and PGE2. These findings lend support to the hypothesis that the PGE series, in a manner similar to adrenergic transmission, are involved in a negative feed-back control mechanism for the transmitter release in cholinergic transmission.     

Neuropeptide Y as a partial agonist of the Y1 receptor

In absence of receptor cycling, human/rat neuropeptide Y was found to persistently occupy the guinea pig neuropeptide Y Y1 receptors expressed on the surface of Chinese hamster ovary (CHO) cells (IC50 approximately 8 nM); a lasting occupancy was also evident with active receptor cycling. A similar blockade was obtained with the human neuropeptide Y Y1 receptor (in CHO or SK-N-MC cells). Peptidic antagonists GR238118 (1229U91) and VD-11 blocked the Y1 receptor in the same molarity range. A neuropeptide Y-related Y1 agonist, (Leu31Pro34) human neuropeptide Y, also strongly adhered to the Y1 site. Similar blockade-like occupancy by neuropeptide Y was found with particulates from Y1-expressing CHO cells, and with native neuropeptide Y Y1 receptors of rat synaptosomes. Peptide YY and a related Y1-selective agonist, (Leu31Pro34) human peptide YY, showed a much less stable binding to the neuropeptide Y Y1 receptor with either the intact cells or particulates. The Y1 binding of neuropeptide Y was also less sensitive to chaotropic agents and guanine nucleotides than the binding of peptide YY, indicating a larger stability for association of neuropeptide Y with the receptor. Inhibition of forskolin-stimulated adenylyl cyclase showed a distinctly attenuating agonism for neuropeptide Y, with an activity similar to peptide YY below 1 nM, but considerably lower above 3 nM of the peptides. This activity was largely exerted via pertussis toxin-sensitive G-proteins of Y1-CHO cells. Our findings indicate that signaling by neuropeptide Y via its Y1 receptor could be self-restricting at higher levels of the peptide, in relation to a strong association of the agonist with the Y1 binding site.     

Characterization of bradykinin-induced prostaglandin E2 release from cultured rat trigeminal ganglion neurones

Bradykinin and prostaglandins are both local mediators strongly implicated in pain and inflammation. Here, we have investigated the effects of bradykinin on the release of prostaglandin E(2) from cultured neurones derived from adult rat trigeminal ganglia. Bradykinin was a potent inducer of prostaglandin E(2) release, an effect that was likely mediated by bradykinin B(2) receptors, as the bradykinin-induced prostaglandin E(2) release was attenuated by the bradykinin B(2) receptor-selective antagonist, arginyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl-3-(2-thienyl)-L-alanyl-L-seryl-D-1,2,3,4-tetrahydro-3-isoquinolinecarbonyl-L-(2 alpha, 3 beta, 7a beta)-octahydro-1H-indole-2-carbonyl-L-arginine (HOE 140), but not by the bradykinin B(1) receptor-selective antagonist, des-Arg(9),[Leu(8)]-bradykinin. Furthermore, bradykinin-induced prostaglandin E(2) release was inhibited following treatment with the phospholipase A(2) inhibitor, arachidonyltrifluoromethyl ketone (AACOCF(3)), the nonselective cyclooxygenase inhibitor, piroxicam, the mitogen-activated protein kinase kinase-1 (MEK1) inhibitor, 2'-amino-3'-methoxyflavone (PD98059), and the protein kinase C inhibitor, bisindolylmaleimide XI (Ro320432). Taken together, these data suggest that bradykinin, acting via bradykinin B(2) receptors, induces prostaglandin E(2) release from trigeminal neurones through the protein kinase C and mitogen-activated protein kinase-dependent activation of phospholipase A(2) and consequent stimulation of cyclooxygenases.     

Interaction of prostaglandin E2 and bradykinin in the induction of afferent splanchnic nerve discharges in cats

In anesthetized cats, the administration of either bradykinin (BK) (0.3-3 micrograms/kg) or prostaglandin E2 (PGE2) (1-30 micrograms/kg) into the cranial mesenteric artery dose-dependently evoked the firing discharge in the proximal end of the afferent greater splanchnic nerves with a latency of about 10 sec, the pronounced contraction of the longitudinal muscle of the jejunum, and changes in blood pressure. PGE2 at the doses of 1-10 micrograms-kg i.a. potentiated the BK (1 microgram/kg i.a.)-induced firing discharge of the afferent splanchnic nerves of which latency was also shortened, but did not alter the BK-induced jejunal contraction and blood pressure change. However, trimoprostil (30 micrograms/kg i.a.), a trimethyl PGE2 derivative, did not change all of these responses to BK. Aspirin at 50 mg/kg i.v. markedly prevented the BK-induced nerve discharges, but not the BK-induced jejunal contraction. These results taken together indicate that PGE2 may be involved in the facilitatory response of afferent splanchnic nerve discharges to BK, but not involved in the BK-induced jejunal contraction and blood pressure change. The findings on trimoprostil present the possibility that derivatization of PGE2 could modify its inherent ability to produce adverse side-effects.