The voltage-sensitive Ca2+ channel (VSCC) antagonists omega-Aga-IVA and omega-CTX-MVIIC inhibit spontaneous epileptiform discharges in the rat cortical wedge.

The ability of VSCC antagonists to modulate excitatory amino acid (EAA) release was evaluated by measuring N-methyl-D-aspartate (NMDA) receptor-dependent spontaneous epileptiform discharges in rat cortical wedges. The N-type channel blocker omega-CTX-GVIA (300 nM) was ineffective. The P-type channel blocker omega-Aga-IVA at 300 nM reduced the frequency of discharges by 63%, while 300 nM omega-CTX-MVIIC reduced the frequency by 35%. These results coupled with the absence of NMDA antagonism by omega-Aga-IVA or omega-CTX-MVIIC in the cortical wedge suggest that the VSCCs blocked by these toxins are primarily responsible for mediating impulse dependent EAA release in the rat neocortex.

Polyamine modulation of excitatory amino acid responses in the rat cortical wedge.

Rat neocortex slices in Mg2+ free buffer show spontaneous discharges which have a constant frequency and are dependent on N-methyl-D-aspartate (NMDA) receptor activation. Spermine increased the frequency of discharges at concentrations below 1 mM, had biphasic effects at 1 mM, and only decreased the frequency of discharges at 3 mM. In contrast, the amplitude of these discharges was only reduced by spermine in a concentration dependent manner (300 microM to 3 mM). Spermidine produced similar effects, but was a less potent inhibitor of discharge frequency and amplitude than spermine. Diethylenetriamine (DET) 300 microM did not significantly inhibit polyamine-induced increases in the discharge frequency. Polyamines inhibited direct depolarizations induced by the glutamate agonists NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in a concentration and time dependent manner. The data are consistent with two sites of action for polyamines, one enhancing the frequency of NMDA-mediated spontaneous epileptiform discharges and the other inhibiting direct glutamate responses in rat cortex. The slow onset (time to maximal enhancement or inhibition by polyamines greater than 30 min) and lack of reversibility with polyamine removal suggest that these sites are intracellular and/or presynaptic.

Cold injury, blood-brain barrier changes, and leukotriene synthesis: inhibition by phenidone.

Transcranial cold injury in rats and guinea pigs induced cerebral extravasation of albumin labeled with Evans blue dye or 125I, respective indicators of the area and amount of blood-brain barrier (BBB) disruption. Radioimmunoassay of brain extracts showed that cold injury induced leukotriene (LT)C4 in rat and guinea pig brains 15 min after injury. In guinea pigs, the LT synthesis inhibitor phenidone (30 mg/kg, i.p.) completely blocked cold-induced LTC4 in brain. Phenidone (30 and 100 mg/kg) also inhibited cerebral tissue accumulation of 125I-albumin and dye in rats and guinea pigs. Phenidone is reported to show antioxidant properties and selective lipoxygenase inhibition of arachidonic acid metabolism compared to cyclooxygenase inhibitors, meclofenamate sodium, and other nonsteroidal anti-inflammatory agents. Since several oxygen and hydroxyl radical scavengers and the cyclooxygenase inhibitor, meclofenamate sodium, did not inhibit protein extravasation, the findings support a role for LT as a mediator of cold-induced changes in BBB permeability in rats and guinea pigs and suggest that the inhibitory effects of phenidone on BBB permeability may be due to inhibition of LT production.

CI-922--a novel, potent antiallergic compound--I. Inhibition of mediator release in vitro.

CI-922 (3,7-dimethoxy-4-phenyl-N-1H-tetrazol-5-yl-4H-furo[3,2-b]-indole- 2-carboxamide, L-arginine salt) is a novel antiallergy compound which inhibits the release of the inflammatory mediators histamine and leukotriene (LT) from stimulated cells. CI-922 showed potent, effective inhibition of antigen-induced mediator release from human basophils and isolated guinea pig lung. The drug inhibited ragweed or housedust-induced histamine release from basophils of allergic human donors (IC50 = 8.6 microM). The antiallergy agents proxicromil (IC50 = 80 microM) and cromolyn (100 microM) were less potent than CI-922 or inactive, respectively. In fragmented lung from actively sensitized guinea pigs, CI-922 (IC50 = 1.5 microM), blocked the antigen-induced production of LT and was a more potent inhibitor of histamine release (IC50 = 13.4 microM) than proxicromil (IC50 = 72.9 microM), or cromolyn (inactive at 1 mM). CI-922 (IC50 = 0.9 microM) completely inhibited repeated contractions of guinea pig lung strips that were induced by low antigen concentration in the presence of antihistamine (H1). Nordihydroguaiaretic acid (NDGA) (IC50 = 2.8 microM), proxicromil (IC50 = 6.2 microM) and the LT antagonist FPL-55712 (IC50 = 3.3 microM) also were fully effective, but cromolyn (300 microM) was inactive. In other experiments, CI-922 (IC50 = 7.0 microM) inhibited a strong, nonrepeatable lung contraction induced with high antigen concentration (histamine responses blocked), and was six times more potent than FPL-55712. Other investigations in isolated tissue preparations showed CI-922 to be a weak inhibitor of LT or histamine-induced effects with no anticholinergic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

CI-922--a novel, potent antiallergic compound--II. Activity in animal models of allergy.

CI-922 (3,7-dimethoxy-4-phenyl-N-1H-tetrazol-5-yl-4H-furo [3,2-b]indole-2-carboxamide, L-arginine salt) is an effective antiallergic in guinea pig, rat, and canine models. This in vivo activity is attributed to its ability to inhibit inflammatory mediator release following antigen challenge in these species. Antigen-induced anaphylaxis in guinea pigs (collapse), which is mediated predominantly by histamine, was prevented by i.p. drug pretreatment. CI-922 (5 mg/kg, i.v.) reduced i.v. antigen-induced falls in pulmonary compliance in mepyramine-pretreated, anesthetized guinea pigs. By comparison, cromolyn sodium was inactive in both guinea pig models. In rats, CI-922 given immediately before antigen challenge (ID50 of 0.29 mg/kg, i.v.) was effective and twice as potent as cromolyn sodium and twenty times more potent than proxicromil in preventing i.v. antigen-induced pulmonary anaphylaxis. In addition, when the drugs were given 10 min before antigen challenge, only CI-922 caused a dose-related reduction of bronchoconstriction. CI-922 did not show direct antagonist activity when tested against a serotonin-induced bronchospasm, and exhibited only slight activity against a histamine-induced bronchospasm. CI-922 (0.3 mg/kg, i.v.) also reduced the bronchospasm caused by aerosol antigen (ascaris) challenge in spontaneously allergic dogs. In contrast, proxicromil was inactive in this dog model. The drug also inhibited passive cutaneous anaphylaxis in rats (ID50 of 0.2 to 0.3 mg/kg, i.v. and 0.7 to 6.4 mg/kg, p.o.). These data illustrate that CI-922 is active in several species in vivo, and has a spectrum of antiallergic activity significantly different from cromolyn-like drugs.

Repeatable antigen-induced contractions of isolated guinea pig lung strips are mediated by leukotriene.

Lung strips from actively sensitized guinea pigs were repeatedly contracted by antigen (ovalbumin, OA) challenge in the presence of the antihistamine (H1) mepyramine. At lower concentrations of OA, hourly challenges gave reproducible and consistent responses. High-concentration OA resulted in desensitization, with two to six contractions being very weak. The antigen concentration affected not only the force of contraction, but other parameters including the time to peak effect, the protraction of the peak effect, and the repeatability of the force and time to peak. Low concentrations of OA induced a response which peaked by 6-8 min and decreased by about 30% after 15 min, while high-concentration OA resulted in a contraction which peaked later and did not relax. These data suggest that different 'early' and 'late' mediators may be involved depending on the 'activation state' or the mechanisms that predominate in the contraction response as a result of the amount of stimulation by antigen. Leukotriene apparently mediates the peak and the 15-min contraction since both were inhibited completely by FPL-55712 (IC50 = 8 microM) or NDGA (IC50 = 5 microM). These repeated, leukotriene-mediated contractions of isolated lung may mimic the clinical situation (chronic exposure to low amounts of antigen) of allergic disease and may be used to study the modulation of lung responses and desensitization phenomena.

Acidic furo[3,2-b]indoles. A new series of potent antiallergy agents.

A series of furo[3,2-b]indole carboxylic acids, tetrazoles, and carbamoyltetrazoles was prepared and tested in vitro with use of a model of active pulmonary anaphylaxis, the modified Schultz-Dale Test (SDT). In this model, isolated guinea pig lung strips are repeatedly challenged with antigen in the presence of an antihistamine (H1). Most of the acidic furo[3,2-b]indoles tested inhibited the leukotriene-mediated lung contraction in a dose-related manner. Compounds with an N-phenyl substituent were more potent (IC50 less than or equal to 5.0 microM) inhibitors of SDT than the N-methyl analogues (IC50 greater than or equal to 22.0 microM). Most of the N-phenyl analogues were more potent in SDT than Fisons' mediator-release inhibitor proxicromil (FPL-57,787; IC50 = 6.3 microM). The most potent furo[3,2-b]indoles were those unsubstituted at C-7 and with N-phenyl, 2-carbamoyltetrazole, and 3-alkoxy substituents. All of the carboxylic acid ester analogues tested were weak or inactive at concentrations of 10-30 microM.