Ifenprodil and SL 82.0715 as cerebral anti-ischemic agents. I. Evidence for efficacy in models of focal cerebral ischemia

Recent studies have strongly implicated the excitatory neurotransmitter glutamate in the cascade of pathological mechanisms that cause neuronal loss after certain types of brain ischemia. The neurotoxic effects of glutamate are mediated, at least in global ischemia, via NMDA receptors. In the present study we have examined the effects of compounds that possess NMDA receptor antagonist properties (ifenprodil, SL 82.0715 [(+/-)-alpha-(4-chlorophenyl)-4-[(4-fluorophenyl)methyl]- 1-piperidineethanol] and 1-[1-(2-thienyl)cyclohexyl]piperidine) on the histological consequences of focal, as opposed to global, cerebral ischemia in both the rat and the cat. Ifenprodil (0.3-3 mg/kg i.v.) administered as a perfusion over 3 hr after occlusion of the feline middle cerebral artery reduced the volume of infarcted tissue (measured 4 days after occlusion) in a dose-related manner. At the highest dose a 42% reduction of infarcted volume was noted, essentially in cortical tissue. In an identical protocol, a derivative of ifenprodil, SL 82.0715, reduced the volume of infarction in a manner comparable to that described for ifenprodil. As SL 82.0715 possesses better p.o. bioavailability, this compound was also evaluated in the rat, again after middle cerebral artery occlusion. First administered 30 min after the induction of ischemia, SL 82.0715 (1 and 10 mg/kg p.o.) reduced infarction volume by 34 and 48%, respectively. The quantitative histology was performed 2 days after middle cerebral artery occlusion. The noncompetitive receptor antagonist, 1-[1-(2-thienyl)cyclohexyl]piperidine, administered (1 mg/kg i.p.) before the induction of focal ischemia, similarly and significantly decreased the final volume of infarction. As both ifenprodil and SL 82.0715 are noncompetitive antagonists of the NMDA receptor, two conclusions may be drawn from the present investigation. First, NMDA antagonism by ifenprodil and its derivative is an effective approach for tissue sparing in animal models of stroke and brain infarction. Second, these pharmacological observations provide evidence for the involvement of excitatory amino-acid induced-neurotoxicity in the evolution and consequences of focal cerebral ischemia.     

Ifenprodil and SL 82.0715 as cerebral antiischemic agents. III. Evidence for antagonistic effects at the polyamine modulatory site within the N-methyl-D-aspartate receptor complex

Ifenprodil and SL 82.0715 are noncompetitive N-methyl-D-aspartate (NMDA) antagonists whose inhibitory actions are not explained by antagonistic effects at any of the three commonly recognized sites within the NMDA receptor complex (recognition, channel and modulatory glycine sites). We presently show that ifenprodil and SL 82.0715 antagonize the effects of NMDA via a selective action at the recently described polyamine modulatory site. Spermine and spermidine (0.5-100 microM) increase the binding of [3H]1-[1-(2-thienyl)cyclohexyl] piperidine to washed rat forebrain membranes in the presence of glutamate (10 microM). This effect is antagonized by ifenprodil and SL 82.0715 (0.1-10 microM) at concentrations which do not displace [3H]1-(2-thienyl)cyclohexyl] piperidine in the absence of added polyamine. Spermine and spermidine (up to 100 microM) do not significantly alter the binding of [3H]glycine but increase the binding of the NMDA recognition site ligand [3H](+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid. Ifenprodil and SL 82.0715 (0.1-10 microM) antagonize this effect; ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-10-imine maleate) or 7-chlorokynurenate (100 microM) are ineffective. In immature rat cerebellar slices, spermine and spermidine (10-1000 microM) potentiate the maximal effects of NMDA (80-160 microM) on cyclic GMP production. Spermine (100-1000 microM) reverses the antagonistic effects of ifenprodil (0.15-50 microM) but not of ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-10-imine acid or kynurenate on the NMDA receptor-mediated increase in cyclic GMP levels. Ifenprodil (0.01-1 microM) potently but only partially antagonizes the depolarizing effects of NMDA (10 microM) on the immature rat spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)     

gamma-Aminobutyric acid (GABA) receptor stimulation. II. Specificity of progabide (SL 76002) and SL 75102 for the GABA receptor

Progabide and its immediate metabolite SL 75102 displace [3H]gamma-aminobutyric acid (GABA), [3H]muscimol and [3H]isoguvacine from their binding sites to membranes prepared from rat brain or human cerebellum and increase (SL 75102) [3H]flunitrazepam binding to rat cerebral cortex membranes. In contrast, these compounds have very weak or no effects on alpha or beta noradrenergic, histamine, muscarinic cholinergic or glycine receptors or on the [3H]imipramine or [3H]kainate binding sites. Neither progabide nor SL 75102 inhibit GABA synthesis, metabolism or uptake. Also, the uptake of norepinephrine, serotonin and dopamine into synaptosomes of cerebral regions is not affected by progabide. [3H]GABA release from substantia nigra slices is decreased by SL 75102 and progabide, in agreement with the hypothesis of a GABAergic autoreceptor controlling GABA release from its nerve terminals. These data suggest a specific agonist action of progabide and SL 75102 on GABA receptors.     

Behavioral tolerance and sensitization to CGS 19755, a competitive N-methyl-D-aspartate receptor antagonist

Competitive N-methyl-D-aspartate (NMDA) receptor antagonists, including CGS 19755, have the ability to antagonize NMDA-induced convulsions, to cause ataxia and, at high doses, to increase spontaneous locomotor activity. It was of interest to determine whether or not repeated treatment with CGS 19755 would induce tolerance to some or all of these effects. CGS 19755 was administered to mice twice daily for 14 days at 54 mg/kg i.p. per injection. One day after the last repeated injection, mice were challenged with vehicle or one of several doses of CGS 19755 (10, 30, 54 and 100 mg/kg) and were tested for evidence of motor impairment (using righting reflex and traction tests), for spontaneous locomotor activity and for the threshold dose of NMDA required to induce convulsions. When challenged with CGS 19755, mice that had previously received only vehicle showed reduced motor activity in response to doses of 54 and 100 mg/kg. In contrast, mice that had received the repeated treatment regimen of CGS 19755 increased motor activity in response to challenge doses of 30 and 54 mg/kg. These effects resembled those reported previously by some investigators for phencyclidine. However, repeated treatment with CGS 19755 induced only slight tolerance to the ability of this drug to cause ataxia. In mice treated repeatedly with CGS 19755, the threshold dose of NMDA to induce convulsions did not differ significantly from that in mice treated repeatedly with vehicle, indicating no demonstrable tolerance to the apparent anticonvulsant effects of CGS 19755 over this time period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absence of an anti-ischemic effect of the peripheral benzodiazepine receptor antagonist PK 11195. Study by atrial stimulation in man

We investigated the anti-ischemic effects of PK 11195 (RP 52028), a selective ligand for peripheral type benzodiazepine binding sites in man. In a first series of patients, we did not find any hemodynamic effect of 10 mg (8 patients) or 20 mg (8 patients) of the intravenously administered drug. The anti-ischemic effect was evaluated on 16 patients with coronary heart disease and a positive stress test in a double blind study of 20 mg of intra-venous PK 11195 (8 patients) versus placebo (8 patients). Ischemia was induced by pacing, and assessed by ST segment depression and lactates extraction before and 15 minutes after administration of the drug. No statistical differences could be found on these ischemia indices between the placebo and PK 11195 treated groups. Although experimental studies have shown interaction of the drug with the calcium channels, our study did not demonstrate any anti-ischemic effect with the dosage used.     

Potent antihyperalgesic activity without tolerance produced by glycine site antagonist of N-methyl-D-aspartate receptor GV196771A.

Central sensitization is a condition of enhanced excitability of spinal cord neurons that contributes to the exaggerated pain sensation associated with chronic tissue or nerve injury. N-methyl-D-aspartate (NMDA) receptors are thought to play a key role in central sensitization. We have tested this hypothesis by characterizing in vitro and in vivo a novel antagonist of the NMDA receptor acting on its glycine site, GV196771A. GV196771A exhibited an elevated affinity for the NMDA glycine binding site in rat cerebral cortex membranes (pKi = 7.56). Moreover, GV196771A competitively and potently antagonized the activation of NMDA receptors produced by glycine in the presence of NMDA in primary cultures of cortical, spinal, and hippocampal neurons (pKB = 7.46, 8. 04, and 7.86, respectively). In isolated baby rat spinal cords, 10 microM GV196771A depressed wind-up, an electrical correlate of central sensitization. The antihyperalgesic properties of GV196771A were studied in a model of chronic constriction injury (CCI) of the rat sciatic nerve and in the mice formalin test. In the CCI model GV196771A (3 mg/kg twice a day p.o.), administered before and then for 10 days after nerve ligature, blocked the development of thermal hyperalgesia. Moreover, GV196771A (1-10 mg/kg p.o.) reversed the hyperalgesia when tested after the establishment of the CCI-induced hyperalgesia. In the formalin test GV196771A (0.1-10 mg/kg p.o.) dose-dependently reduced the duration of the licking time of the late phase. These antihyperalgesic properties were not accompanied by development of tolerance. These observations strengthen the view that NMDA receptors play a key role in the events underlying plastic phenomena, including hyperalgesia. Moreover, antagonists of the NMDA glycine site receptor could represent a new analgesic class, effective in conditions not sensitive to classical opioids.     

An antagonist/partial agonist at the polyamine recognition site of the N-methyl-D-aspartate receptor that alters the properties of the glutamate recognition site.

The effects of N-(3-aminopropyl)-1,10-diaminodecane (APDA10) on the N-methyl-D-aspartate (NMDA) receptor/ion channel complex were investigated. In the presence of 100 microM glutamate and 100 microM glycine, APDA10 had biphasic effects on the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imin e (MK-801) to NMDA receptors on well washed synaptic plasma membranes. The maximal stimulation of binding by APDA10 was less than that seen with spermine. In the presence of glutamate and glycine, APDA10 attenuated the stimulatory effect of spermine and the inhibitory effect of 1,10-diaminodecane. In the nominal absence of glutamate and glycine, APDA10 had no effect on the binding of [3H]MK-801, but antagonized the stimulatory effect of spermine on the binding of [3H] MK-801. These data suggest that APDA10 acts as a mixed antagonist/partial agonist at the polyamine recognition site, and that the partial agonist properties of APDA10 are dependent on the activation state of the receptor complex. An increase in the potency of the glutamate site antagonists D-2-amino-5-phosphonovaleric acid and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid for inhibiting the binding of [3H]MK-801 was seen in the presence of APDA10. APDA10 also increased the affinity of binding of [3H]3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid to the NMDA receptor complex but had no effect on the binding of [3H]glycine. These data suggest that the polyamine APDA10 may alter the properties of the glutamate recognition site on the NMDA receptor complex.     

Interleukin-1 receptor antagonist as therapy for inflammatory disorders

IL-1 is a pivotal mediator of the immune response and has been implicated in inflammatory and infectious diseases. As a consequence, the administration of IL-1 receptor antagonist (IL-1ra), a recombinantly synthesised endogenous inhibitor of IL-1, has appeal as a therapeutic strategy in these conditions. To date, the largest clinical experiences with IL-1ra have been in the setting of sepsis and rheumatoid arthritis (RA). Like other anti-inflammatory agents that target a specific mediator, IL-1ra was found to lack efficacy when given in conjunction with standard therapy in patients with sepsis and septic shock. In contrast, recent studies enrolling patients with RA suggest that IL-1ra significantly ameliorates disease activity and retards joint destruction. Whether the respective lack of efficacy and success of IL-1ra in these two diseases is a result of differences in the pathologic processes involved, or reflects the nature in which the clinical studies were conducted, is unclear. Further, the effectiveness of IL-1ra compared to other anticytokine and conventional treatments in RA remains to be clarified. Nonetheless, the recent finding that IL-1ra has the ability to favourably influence a chronic inflammatory disease supports the hypothesis that inhibition of a single mediator of the immune response may have clinical impact.     

Biological properties of recombinant human monocyte-derived interleukin 1 receptor antagonist.

Human monocytes cultured on adherent IgG produce a specific IL-1 inhibitor that functions as a receptor antagonist (IL-1ra). This molecular has been purified, sequenced, cloned as a cDNA, and expressed in Escherichia coli. Recombinant IL-1ra has 17,000 mol wt and binds to IL-1 receptors on T lymphocytes, synovial cells, and chondrocytes with an affinity nearly equal to that of IL-1. These studies have examined some biological properties of purified recombinant human IL-1ra. This protein exhibits a dose-responsive inhibition of Il-1 alpha and Il-1 beta augmentation of PHA-induced murine thymocyte proliferation. The recombinant IL-1ra also blocks IL-1 alpha and IL-1 beta stimulation of PGE2 production in human synovial cells and rabbit articular chondrocytes, and of collagenase production by the synovial cells. A 50% inhibition of these IL-1-induced biological responses requires amounts of IL-1ra up to 100-fold in excess of the amounts of IL-1 alpha or IL-1 beta present. IL-1ra may play an important role in normal physiology or in pathophysiological states by functioning as a natural IL-1 receptor antagonist in the cell microenvironment.     

Angiotensin II receptor antagonists as the agents to treat cerebrovascular disease]

Recently, several antagonists of angiotensin II receptors (AII-A) have been developed and are now used as antihypertensive agents. The regional cerebral blood flow appears to show typical changes during the course of cerebral ischemia and AII-A may have a favorable effect on the flow in some situations. Moreover, activation of the renin-angiotensin system plays an important role in the development of cerebrovascular lesions in chronic hypertension. Because several enzymes appear to produce angiotensin II in the absence of classical renin-angiotensin system, it is possible that angiotensin II is produced in some blood vessels even after inhibition of the activity of ACE. Thus, AII-A may be more effective to treat cerebrovascular lesions during hypertension than ACE inhibitors.     

Differential actions of antiparkinson agents at multiple classes of monoaminergic receptor. II. Agonist and antagonist properties at subtypes of dopamine D(2)-like receptor and alpha(1)/alpha(2)-adrenoceptor

The accompanying multivariate analysis of the binding profiles of antiparkinson agents revealed contrasting patterns of affinities at diverse classes of monoaminergic receptor. Herein, we characterized efficacies at human (h)D(2SHORT(S)), hD(2LONG(L)), hD(3), and hD(4.4) receptors and at halpha(2A)-, halpha(2B)-, halpha(2C)-, and halpha(1A)-adrenoceptors (ARs). As determined by guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding, no ligand displayed "full" efficacy relative to dopamine (100%) at all "D(2)-like" sites. However, at hD(2S) receptors quinpirole, pramipexole, ropinirole, quinerolane, pergolide, and cabergoline were as efficacious as dopamine (E(max)100%); TL99, talipexole, and apomorphine were highly efficacious (79-92%); piribedil, lisuride, bromocriptine, and terguride showed intermediate efficacy (40-55%); and roxindole displayed low efficacy (11%). For all drugs, efficacies were lower at hD(2L) receptors, with terguride and roxindole acting as antagonists. At hD(3) receptors, efficacies ranged from 33% (roxindole) to 94% (TL99), whereas, for hD(4) receptors, highest efficacies (approximately 70%) were seen for quinerolane, quinpirole, and TL99, whereas piribedil and terguride behaved as antagonists and bromocriptine was inactive. Although efficacies at hD(2S) versus hD(2L) sites were highly correlated (r = 0.79), they correlated only modestly to hD(3)/hD(4) sites (r = 0.44-0.59). In [(35)S]GTPgammaS studies of halpha(2A)-ARs, TL99 (108%), pramipexole (52%), talipexole (51%), pergolide (31%), apomorphine (16%), and quinerolane (11%) were agonists and ropinirole and roxindole were inactive, whereas piribedil and other agents were antagonists. Similar findings were obtained at halpha(2B)- and halpha(2C)-ARs. Using [(3)H]phosphatidylinositol depletion, roxindole, bromocriptine, lisuride, and terguride displayed potent antagonist properties at halpha(1A)-ARs. In conclusion, antiparkinson agents display diverse agonist and antagonist properties at multiple subtypes of D(2)-like receptor and alpha(1)/alpha(2)-AR, actions, which likely contribute to their contrasting functional profiles.     

CHF3381, a N-methyl-D-aspartate receptor antagonist and monoamine oxidase-A inhibitor, attenuates secondary hyperalgesia in a human pain model.

CHF3381 is a new low-affinity, noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist and reversible monoamine oxidase-A (MAO-A) inhibitor. The analgesic activity of CHF3381 was investigated in the heat-capsaicin human pain model and compared with those of gabapentin. Twenty-seven young, healthy male volunteers received a single oral dose of CHF3381 (500 mg), gabapentin (1,200 mg), or placebo in a randomized, double-blind, crossover study design. Measurements were done before and 135 to 145 minutes after treatment administration and included area of secondary hyperalgesia around the sensitized skin of the forearm (45 degrees C for 5 minutes followed by topical capsaicin for 30 minutes), area of secondary hyperalgesia after thermal sensitization of the thigh (45 degrees C for 3 minutes), heat pain detection thresholds (degrees C), and pain on a visual analogue scale after long thermal stimulation (45 degrees C for 1 minute). Compared with placebo, both gabapentin and CHF3381 significantly reduced the area of secondary hyperalgesia on the dominant forearm. Median (and interquartile range) percent values over baseline were 86% after placebo (69% to 100%), 56% (41% to 76%) after gabapentin (P < .001), and 67% (49% to 88%) after CHF3381 (P < .009). Both drugs also significantly decreased the area of secondary hyperalgesia on the dominant thigh. The other pain variables were not significantly affected. Adverse events, mainly fatigue and dizziness, were mild to moderate. PERSPECTIVE: This article presents the antihyperalgesic effect of CHF3381, a new NMDA receptor antagonist and reversible MAO-A inhibitor, in a human pain model and might guide the proper selection of CHF3381 doses to be used in Phase 2 studies in patients with neuropathic pain.     

Interactions between an N-methyl-D-aspartate antagonist and low-efficacy opioid receptor agonists in assays of schedule-controlled responding and thermal nociception

A growing body of literature has implicated N-methyl-d-aspartate (NMDA) receptor mechanisms in the acute antinociceptive effects of morphine; however, the nature of this interaction has not been thoroughly quantified. Moreover, it is not clear whether NMDA/morphine interactions extend to less efficacious opioids. Therefore, the present study examined the effects of morphine and various low-efficacy opioid agonists in combination with the NMDA antagonist (-)-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid (LY235959) in two different assays: schedule-controlled responding and thermal nociception. Data were examined with dose-addition analysis to provide a quantitative assessment of the drug interactions. LY235959 and the opioid agonists morphine, buprenorphine, butorphanol, and nalbuphine all decreased rates of schedule-controlled responding. LY235959/morphine and LY235959/buprenorphine mixtures produced additive or subadditive effects in this assay, whereas LY235959/butorphanol and LY235959/nalbuphine mixtures produced additive or supra-additive effects, depending on the relative proportions of each drug in mixture. Morphine, buprenorphine, butorphanol, and nalbuphine also produced dose-dependent antinociception in the assay of thermal nociception, whereas LY235959 failed to produce an effect. In this assay, LY235959 potentiated the antinociceptive effects of morphine and each of the low-efficacy opioids tested. These results suggest that LY235959 may selectively increase the antinociceptive effects of morphine and some low-efficacy opioid receptor agonists without increasing their rate-altering effects. In addition, these data confirm that the behavioral effects of drug mixtures depend on the relative concentrations of the drugs in the mixture and on the endpoint under study.     

Pharmacological characterization of the nonpeptide angiotensin II receptor antagonist, SK&F 108566.

The angiotensin II (AII) antagonist activity of (E)-alpha-[[2-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5- yl]methylene]-2-thiophenepropanoic acid (SK&F 108566), was examined in a number of in vitro and in vivo assays. In rat and human adrenal cortical membranes, SK&F 108566 displaced specifically bound [125I]AII with IC50 of 9.2 and 3.9 nM, respectively. SK&F 108566 also inhibited [125I]AII binding to human liver membranes (IC50 = 1.7 nM) and to rat mesenteric artery membranes (IC50 = 1.5 nM). In rabbit aortic smooth muscle cells, SK&F 108566 caused a concentration-dependent inhibition of AII-induced increases in intracellular Ca++ levels. In rabbit aortic rings, SK&F 108566 produced parallel rightward shifts in the AII concentration-response curve without affecting the maximal contractile response. Schild analysis of the data yielded a KB value of 0.26 nM and a slope not different from 1, indicative of competition antagonism. SK&F 108566 had no effect on the contractile responses to KCl, norepinephrine or endothelin in rabbit aorta. In conscious normotensive rats, i.v. administration of SK&F 108566 (0.01-0.3 mg/kg) produced dose-dependent parallel shifts in the AII pressor dose-response curve. Administration of SK&F 108566 (3-10 mg/kg) intraduodenally or intragastrically to conscious normotensive rats resulted in a dose-dependent inhibition of the pressor response to AII (250 ng/kg, i.v.). At 10 mg/kg, i.d., significant inhibition of the pressor response to AII was observed for 3 hr. In this same rat model, SK&F 108566 had no effect on base-line pressure or on the pressor response to norepinephrine or vasopressin. The data demonstrate that SK&F 108566 is a potent, highly selective, competitive nonpeptide AII antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

CPP, a selective N-methyl-D-aspartate (NMDA)-type receptor antagonist: characterization in vitro and in vivo

3-(2-Carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) was synthesized as a rigid analog of 2-amino-7-phosphonoheptanoate, a previously known antagonist at the N-methyl-D-aspartate (NMDA) preferring, or NMDA-type, of excitatory amino acid receptor. CPP was found to be a potent, selective and competitive antagonist of NMDA-type receptors. CPP antagonized with an IC50 of 8 muM [3H]ACh release which was evoked from rat striatal brain slices by NMDA (50 muM). In contrast, the release of [3H]ACh evoked by elevated KCI was not inhibited by CPP even at a concentration of 100 muM. The antagonism by CPP of NMDA-evoked [3H]ACh release was competitive, with a pA2 of 5.66 for CPP, compared with a pA2 value of 5.22 for 2-amino-7-phosphonoheptanoate. CPP affected neither the uptake of L-[3H]glutamate nor the inhibition by aconitine of L-[3H]glutamate uptake, suggesting a lack of membrane-stabilizing or local anesthetic effects, and also suggesting that CPP itself may not be taken up through the L-glutamate membrane transporter. Moreover, [3H] CPP was not accumulated by synaptosomes (P2 fraction) which avidly accumulate L-[3H]glutamate, supporting the concept that this NMDA-type receptor antagonist acts at an NMDA-type receptor on the external surface of the plasma membrane. CPP (10 muM) failed to interact with any of 21 other putative neurotransmitter receptors including alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding (quisqualate-type receptor) and [3H]kainate binding (kainate-type receptor). Audiogenic convulsions in DBA/2 mice were blocked by CPP (ED50 = 1.5 mg/kg i.p.) as were NMDA-induced seizures in CF-1 mice (ED50 = 1.9 mg/kg i.p.). In both strains, CPP impaired the traction reflex at higher doses (ED50 = 6.8 mg/kg and 6.1 mg/kg and 6.1 mg/kg i.p. for DBA/2 and CF-1, respectively). The traction reflex impairment by CPP may be due to muscle relaxant effects of the compound, an explanation supported by the finding that CPP reduced muscle tone as assessed by electromyogram measurement in animals whose muscle tone had been increased by opiate administration. Finally, cerebellar cyclic GMP levels, known to be sensitive to neurotransmission via NMDA-type receptors, were decreased by CPP (ED50 = 4.7 mg/kg i.p.) in mice. In conclusion, based upon the competitive antagonism by CPP of NMDA-evoked [3H] ACh release in vitro and the antagonism of NMDA-induced convulsions in vivo, the data presented are consistent with competitive antagonism of NMDA-type receptors.     

Effects of the N-methyl-D-aspartate receptor antagonist dextromethorphan on temporal summation of pain are similar in fibromyalgia patients and normal control subjects.

Temporal summation of second pain at least partly reflects temporal summation of dorsal horn neuronal responses, and both have been termed windup (WU), a form of nociception-dependent central sensitization. Animal and human experiments have shown that both forms of WU depend on N-methyl-D-aspartate (NMDA) and substance P receptor systems. WU of second pain (WU(SP)) in patients with fibromyalgia (FM) is enhanced compared with normal control (NC) subjects and is followed by exaggerated WU(SP) aftersensations and prolonged WU(SP) maintenance at low stimulus frequencies. Because the enhanced WU(SP) of FM patients could be related to abnormal endogenous modulation of NDMA receptors, we tested the effects of the NMDA receptor antagonist dextromethorphan (DEX) on WU(SP) in FM and NC subjects in a double-blind, placebo-controlled, crossover study. WU(SP) was elicited by trains of 0.7-second duration thermal pulses applied to the glabrous surface of the hands or by 1-second mechanical stimuli to the adductor pollicis muscle of the hands at a frequency of 0.33 Hz. In comparison to baseline and placebo conditions, single oral doses of DEX 60 and 90 mg reduced thermal and mechanical WU(SP) in NC and FM subjects, with DEX 90 mg being most effective. These effects did not differ for male and female NC subjects. FM subjects required less thermal and mechanical stimulus intensity than NC to achieve maximal WU(SP), but the extent of WU(SP) reduction by DEX did not statistically differ between NC and FM subjects for all study conditions. Thus, central pain processing of FM subjects is not different from NC in at least one important aspect, namely their NMDA receptor system responsiveness to pharmacologic inhibition by DEX. PERSPECTIVE: Results of this study demonstrate that FM patients show abnormal WU(SP) during thermal and mechanical stimulation compared with NC. Because oral doses of the NMDA receptor antagonist DEX attenuated thermal and mechanical WU(SP) similarly in FM patients and NC, other mechanisms than WU(SP) need to be considered for the widespread pain of FM patients. These mechanisms might include tonic nociceptive input from peripheral tissues and/or enhanced descending facilitation.     

Co-localization of mu opioid receptor and N-methyl-D-aspartate receptor in the trigeminal dorsal horn.

Antagonists acting at the N-methyl-D-aspartate (NMDA) receptor can block the development of tolerance to the analgesic effects of [mu ] opioid receptor (MOR) ligands, such as morphine, and can also enhance the analgesic efficacy of opioids. These findings have led to the hypothesis that interactions between NMDA receptor and MOR ligands may be due to the co-localization of these receptors on neurons in the dorsal horn. We used dual immunogold and immunoperoxidase immunocytochemistry for MOR1 and NMDAR1 to determine the degree of co-localization of these receptors in neurons of the trigeminal dorsal horn. By use of electron microscopy, we found that both receptors were primarily located in dendrites and to a lesser extent in perikarya, axons, axon terminals, and glia. With regard to the degree of co-localization in dendrites, 63% of MOR1-labeled dendrites also contained NMDAR1, whereas 61% of NMDAR1-labeled dendrites also contained MOR1. Most of the dual-labeled profiles (94%) were classified as dendrites, with the remainder being axons, axon terminals, or perikarya. These results suggest that direct interactions between MOR and NMDA receptor ligands are likely mediated through shared dendritic targets in the dorsal horn. Less frequently, we found evidence for modulation of afferents to MOR-containing neurons through presynaptic NMDA receptors.     

In vitro pharmacology of a nonpeptidic angiotensin II receptor antagonist, SC-51316.

The properties of a novel nonpeptidic angiotensin II (AII) receptor antagonist, 2,5-dibutyl-2,4-dihydro-4-([2-(1H-tetrazol-5-yl)(1,1'-biphenyl) -4'-yl]methyl)-3H-1,2,4-triazol-3-one (SC-51316), are described. SC-51316 inhibited [125I]AII binding selectively to the AT1 receptor with IC50 values of 3.6 and 5.1 nM in rat adrenal cortical and rat uterine membrane preparations, respectively. The compound was a competitive and reversible antagonist of AII-mediated contraction of rabbit aortic rings with a pA2 of 8.86. In addition, SC-51316 inhibited AII-induced aldosterone release from rat adrenal zona glomerulosa cells and blocked inhibition of renin release by AII from rat kidney slices with pA2 values of 8.62 and 8.9, respectively. The agent (0.1 mM) did not inhibit angiotensin-converting enzyme or plasma renin activity. These data demonstrate that SC-51316 is a potent AII receptor antagonist which may prove to be useful as a pharmacologic tool for studying the role of the renin-angiotensin system in cardiovascular diseases.     

The antihypertensive effect of the angiotensin II receptor antagonist DuP 753 may not be due solely to angiotensin II receptor antagonism.

The angiotensin II (AII) receptor antagonist, DuP 753 (10 mg/kg intraduodenal), produced a sustained and long-lasting antihypertensive effect in conscious renin-dependent hypertensive rats. Blood pressures were still reduced markedly 24 to 72 hr after administration of a single dose of DuP 753. However, pressor responses elicited by either angiotensin I or AII were not blocked at these times despite the continued antihypertensive effect of DuP 753. In a model of orthostatic hypotension, DuP 753 and the selective alpha-1 adrenoceptor antagonist prazosin produced a marked orthostatic hypotension response in renin-dependent hypertensive rats as demonstrated by potentiation of the decrease in blood pressure induced by a 90 degrees tilt. The nonpeptide AII receptor antagonist SK&F 108566 (10 mg/kg intraduodenal) did not produce orthostatic hypotension and the angiotensin converting enzyme inhibitor enalapril produced only a slight orthostatic response to tilting. In conscious spontaneously hypertensive rats (SHR), allowed 3 to 4 days to recover from surgery, administration of either enalapril (1 mg/kg i.v.) or SK&F 108566 (10 mg/kg i.v.) did not significantly effect blood pressure. In SHR tested within 24 hr of surgery, enalapril was effective in lowering blood pressure. In contrast, in surgically recovered SHR, DuP 753 (10 mg/kg i.v.) produced an antihypertensive effect that was slow in onset, sustained and extremely long in duration. Blood pressures did not return to predrug levels until 48 hr after administration of DuP 753. Stimulation of the thoracolumbar sympathetic outflow in pithed rats produced frequency-dependent pressor responses that were significantly potentiated by continuous infusion of a subpressor dose of AII.(ABSTRACT TRUNCATED AT 250 WORDS)