Effects of a contractile prostaglandin antagonist (L-640,035) upon allergen-induced bronchoconstriction in hyperreactive rats and conscious squirrel monkeys

The effects of an antagonist of contractile prostanoids, L-640,035 (3-hydroxymethyl-dibenzo[b,f]thiepin-5-dioxide) upon antigen-induced bronchoconstriction have been studied in inbred rats with non-specific bronchial hyperreactivity and in conscious squirrel monkeys. L-640,035 was a potent inhibitor of antigen-induced dyspnea (ED50 3.1 mg/kg p.o.) in inbred rats pretreated with methysergide (3 micrograms/kg i.v.) but produced no significant inhibition in untreated rats. Administration of L-640,035 (10 mg/kg p.o.) to conscious squirrel monkeys exposed to aerosols of ascaris antigen markedly inhibited changes in pulmonary resistance (RL) and dynamic compliance (CDYN). At a lower dose (1 mg/kg p.o.) the inhibition of changes in CDYN were similar but the effects on RL were reduced. It was concluded first that contractile prostanoids may be important mediators of antigen-induced bronchoconstriction and secondly that L-640,035 may be effective in human allergic asthma.     

L-663,536 (MK-886) (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2 - dimethylpropanoic acid), a novel, orally active leukotriene biosynthesis inhibitor

L-663,536 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2, 2-dimethylpropanoic acid) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human polymorphonuclear leukocytes (PMN) (IC50, 2.5 nM). Similarly, L-663,536 inhibited A23187-induced LTB4 formation by rat peripheral blood and elicited PMN. At concentrations where inhibition of leukotriene biosynthesis occurred in human whole blood (1.1 microM), no effect was seen on cyclooxygenase or 12-lipoxygenase, an effect also observed in washed human platelets. The compound had no effect on rat or porcine 5-lipoxygenase indicating that L-663,536 is not a direct 5-lipoxygenase inhibitor. When administered in vivo L-663,536 was a potent inhibitor of antigen-induced dyspnea in inbred rats pretreated with methysergide (ED50, 0.036 mg/kg p.o.) and of Ascaris-induced bronchoconstriction in squirrel monkeys (1 mg/kg p.o.). The compound inhibited leukotriene biosynthesis in vivo in a rat pleurisy model (ED50, 0.2 mg/kg p.o.), an inflamed rat paw model (ED50, 0.8 mg/kg), a model of leukotriene excretion in rat bile following antigen provocation, and a model in the guinea-pig ear where leukotriene synthesis was induced by topical challenge with ionophore A23187 (ED50, 2.5 mg/kg p.o. and 0.6 micrograms topically). The results indicate that L-663,536 is a potent inhibitor of leukotriene biosynthesis both in vitro and in vivo indicating that the compound is suitable for studying the role of leukotrienes in a variety of pathological situations.     

Pharmacology of L-660,711 (MK-571): a novel potent and selective leukotriene D4 receptor antagonist

L-660,711 (3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl) ((3-dimethyl amino-3-oxo propyl)thio)methyl)thio)propanoic acid is a potent and selective competitive inhibitor of [3H]leukotriene D4 binding in guinea pig (Ki value, 0.22 nM) and human (Ki value, 2.1 nM) lung membranes but is essentially inactive versus [3H]leukotriene C4 binding (IC50 value in guinea pig lung, 23 microM). Functionally it competitively antagonized contractions of guinea pig trachea and ileum induced by leukotriene (LT) D4 (respective pA2 values, 9.4 and 10.5) and LTE4 (respective pA2 values, 9.1 and 10.4) and contractions of human trachea induced by LTD4 (pA2 value, 8.5). L-660,711 (5.8 x 10(-8)M) antagonized contractions of guinea pig trachea induced by LTC4 in the absence (dose ratio = 28) but not in the presence of 45 mM L-serine borate (dose ratio less than 2). L-660,711 (1.9 x 10(-5)M) did not block contractions of guinea pig trachea induced by histamine, acetylcholine, 5-hydroxytryptamine, PGF2 alpha, U-44069, or PGD2. In the presence of atropine, mepyramine, and indomethacin, L-660,711 (1.9 x 10(-5)M) inhibited a small component of the response to antigen on guinea pig trachea but completely blocked anti-IgE-induced contractions of human trachea. L-660,711 (i.v.) antagonized bronchoconstriction induced in anesthetized guinea pigs by i.v. LTC4, LTD4, and LTE4 but did not block bronchoconstriction to arachidonic acid, U-44069, 5-hydroxytryptamine, histamine, or acetylcholine. Intraduodenal L-660,711 antagonized LTD4 (0.2-12.8 micrograms/kg)-induced bronchoconstriction in guinea pigs, and p.o. L-660,711 blocked LTD4- and Ascaris-induced bronchoconstriction in conscious squirrel monkeys and ovalbumin-induced bronchoconstriction in conscious sensitized rats treated with methysergide (3 micrograms/kg). The pharmacological profile of L-660,711 indicates that it is a potent, selective, orally active leukotriene receptor antagonist which is well suited to determine the role played by LTD4 and LTE4 in asthma and other pathophysiologic conditions.     

Pharmacology of MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)- indol-2-yl]-2,2-dimethyl propanoic acid), a potent, orally active leukotriene biosynthesis inhibitor.

MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)- indol-2-yl]-2,2-dimethyl propanoic acid, previously L-686,708) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human and elicited rat polymorphonuclear leukocytes (PMNLs) (IC50 values 3.1 and 6.1 nM, respectively) and in human, squirrel monkey, and rat whole blood (IC50 values 510, 69, and 9 nM, respectively). MK-0591 had no effect on rat 5-lipoxygenase. MK-0591 has a high affinity for 5-lipoxygenase activating protein (FLAP) as evidenced by an IC50 value of 1.6 nM in a FLAP binding assay and inhibition of the photoaffinity labelling of FLAP by two different photoaffinity ligands. Inhibition of activation of 5-lipoxygenase was shown through inhibition of the translocation of the enzyme from the cytosol to the membrane in human PMNLs. MK-0591 was a potent inhibitor of LT biosynthesis in vivo, first, following ex vivo challenge of blood obtained from treated rats and squirrel monkeys, second, in a rat pleurisy model, and, third, as monitored by inhibition of the urinary excretion of LTE4 in antigen-challenged allergic sheep. Inhibition of antigen-induced bronchoconstriction by MK-0591 was observed in inbred rats pretreated with methysergide, Ascaris-challenged squirrel monkeys, and Ascaris-challenged sheep (early and late phase response). These results indicate that MK-0591 is a potent inhibitor of LT biosynthesis both in vitro and in vivo indicating that the compound will be suitable for assessing the role of leukotrienes in pathological situations.     

Pulmonary and cardiovascular changes in hyperreactive rats from citric acid aerosols

Administration of aerosols of citric acid to anesthetized spontaneously breathing hyperreactive rats produced reversible increases in respiratory rate (f) and pleural pressure (Ppl) accompanied by hypotension and bradycardia. In contrast, Fischer rats, which do not have bronchial hyperreactivity, failed to respond to citric acid aerosols. The effects of various treatments on citric acid-induced changes in f, Ppl and blood pressure were studied. Vagotomy, cromolyn sodium (1 and 10 mg/kg iv), mecamylamine, (2 mg/kg iv), FPL-55712 (3 mg/kg iv), and BW 755C (10 mg/kg iv) inhibited markedly the responses to citric acid, whereas atropine (2 mg/kg iv) produced weak inhibition. Methysergide (1 mg/kg iv), indomethacin (1 mg/kg iv), and a prostanoid antagonist, L-640,035, (5 mg/kg iv) were completely ineffective. The results suggest that citric acid-induced bronchoconstriction in hyperreactive rats may be reflex mediated and that leukotrienes may be involved in the response.     

L-656,224 (7-chloro-2-[(4-methoxyphenyl)methyl]-3- methyl-5-propyl-4-benzofuranol): a novel, selective, orally active 5-lipoxygenase inhibitor

L-656,224 (7-chloro-2-[(4-methoxyphenyl)methyl]-3-methyl-5-propyl-4-benzofuranol) was a potent inhibitor of leukotriene biosynthesis in intact rat and human leukocytes and CXBG mastocytoma cells (IC50 values, 18-240 nM) and of crude human leukocyte and highly purified porcine leukocyte 5-lipoxygenase (IC50 value, 4 X 10(-7) M). The selectivity of L-656,224 for 5-lipoxygenase was shown through the relative lack of activity of the compound on 12-lipoxygenase, 15-lipoxygenase, cyclooxygenase, catalase, and myeloperoxidase. The compound showed (i) oral activity against hyperalgesia induced in the rat paw by injection of yeast or platelet-activating factor, (ii) dyspnea in sensitized inbred rats induced by an aerosol of antigen, and (iii) bronchoconstriction induced by an aerosol of Ascaris in squirrel monkeys, suggesting a role for 5-lipoxygenase inhibitors in the treatment of asthma and peripheral pain.     

Removal of thallium by combining desferrioxamine and deferiprone chelators in rats

The hypothesis that two known chelators deferiprone (1,2-dimethy1-3-hydroxypyrid-4-one, L₁) and desferrioxamine (DFO) might be more efficient as combined treatment than as monotherapies in removing thallium from the body was tested in rats. Six-week-old male Wistar rats received chelators: L₁ (p.o.), DFO (i.p.) or L₁ + DFO as 110 or 220 mg/kg dose half an hour after a single i.p. administration of 8 mg Tl/kg body weight in the form of chloride. Serum thallium concentration, urinary thallium and iron excretions were determined by graphite furnace atomic absorption spectrometry. Both chelators were effective only at the higher dose level, while DFO was more effective than L₁ in enhancing urinary thallium excretion, L₁ was more effective than DFO in enhancing urinary iron excretion. In the combined treatment group, L₁ did not increase the DFO effect on thallium and DFO did not increase the effect of L₁ on iron elimination. Our results support the usefulness of this animal model for preliminary in vivo testing of thallium chelators. Urinary values were more useful because of the high variability of serum results. Result of combined chelators treatment should be confirmed in a different experimental model before extrapolation to other systems.     

Discovery of a substituted 8-arylquinoline series of PDE4 inhibitors: structure-activity relationship, optimization, and identification of a highly potent, well tolerated, PDE4 inhibitor

The discovery and SAR of a new series of substituted 8-arylquinoline PDE4 inhibitors are herein described. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of emesis to efficacy in several animal models. Typical optimized compounds from this series are potent inhibitors of PDE4 (IC(50)<1nM) and also of LPS-induced TNF-alpha release in human whole blood (IC(50)<0.5microM). The same compounds are potent inhibitors of ovalbumin-induced bronchoconstriction in conscious guinea pigs (EC(50)<0.1mg/kg ip) but require a dose of about 10mg/kg po in the squirrel monkey to produce an emetic response. From this series of compounds, 23a (L-454,560) was identified as an optimized compound.     

Angiotensin-converting enzyme inhibitory and antihypertensive activities of pivalopril (RHC 3659-(S))

Pivalopril (RHC 3659-(S); (S)-N-cyclopentyl-N-(2-methyl-3-pivaloylthiopropionyl) glycine) is a new compound with a hindered sulfur group that has been compared to captopril for oral angiotensin-converting enzyme (ACE) inhibition in rats and dogs and antihypertensive activity in rats. In separate groups of conscious normotensive rats, pivalopril (0.03-1.0 mg/kg, orally [p.o.]) produced a dose-related antagonism of angiotensin I (AngI)-induced pressor effects. The ED50 for pivalopril and captopril was 0.1 mg/kg. In conscious normotensive dogs, pivalopril (incremental doses of 0.01-1.0 mg/kg, p.o.) produced a dose-related antagonism of AngI pressor effects. The ED50 was 0.17 mg/kg for pivalopril and 0.06 mg/kg for captopril. At equieffective doses the two compounds had similar durations of action. In sodium-deficient, conscious spontaneously hypertensive rats (SHR), pivalopril (1-100 mg/kg, p.o.) produced a dose-related reduction in mean arterial pressure. The potency and duration were similar to those of captopril. In the sodium-replete SHR, 5 days of oral dosing with pivalopril, 100 mg/(kg . day), decreased mean arterial pressure more effectively than captopril, 100 mg/(kg . day). No tolerance developed to the antihypertensive effect of either drug. It is concluded that pivalopril is a potent, orally effective ACE inhibitor and antihypertensive agent.     

Potent bronchoconstrictor effects of aerosolized prostaglandin D2 in dogs

Previously, we demonstrated that prostaglandin D₂ (PGD₂), a natural product of the endoperoxide PGH₂, evoked bronchoconstriction when given I.V. to dogs (PROSTAGLANDINS $\text{13}$:255–269, 1977). The present investigation in anesthetized dogs demonstrated that aerosols of PGD₂ (0.001–0.1%) produced concentration-dependent increases in pulmonary resistance (R_L) and decreases in dynamic lung compliance (C_DYN) which were short-lived and equipotent to PGF_2α. These alterations in pulmonary mechanics were partially, yet significantly, inhibited by atropine, thereby suggesting that at least a portion of the bronchoconstriction may be cholinergically mediated. Concomitant cardiovascular depressant effects of both PGD₂ and PGF_2α aerosols were much less and more variable than their bronchopulmonary effects.These results demonstrate a potent bronchoconstrictor effect of aerosolized PGD₂ in dogs. PGD₂ warrants further attention as a possible mediator of the bronchospasm seen in acute, reversible airways obstruction.     

5‐HT1A Activation Counteracts Cardiovascular But Not Hypophagic Effects of Sibutramine in Rats

The noradrenaline (NA) and serotonin reuptake inhibitor, sibutramine, gives effective weight loss, but full efficacy cannot be attained at approved doses due to cardiovascular side effects. We assessed in rats the contributions of NA and serotonin transporters to sibutramine's hypophagic and cardiovascular effects, and whether selective 5‐hydroxytryptamine (5‐HT_1A) receptor activation could counteract the latter without affecting the former. Food intake was assessed in freely feeding rats and cardiovascular parameters in conscious telemetered rats. Ex vivo radioligand binding was used to estimate brain monoamine transporter occupancy. Sibutramine (1–10 mg/kg p.o.) dose‐dependently reduced food intake; however, 10 mg/kg p.o. markedly elevated blood pressure and heart rate. Sibutramine gave greater occupancy of NA than serotonin reuptake sites. Coadministration of the selective 5‐HT_1A agonist F‐11440 (2.5 mg/kg p.o.) attenuated sibutramine‐induced hypertension and tachycardia without altering its food intake effects. The selective NA reuptake inhibitors, nisoxetine or reboxetine, did not alter food intake alone, but each reduced food intake when combined with F‐11440. These results suggest that sibutramine‐induced hypophagic and cardiovascular effects are largely due to increased brain synaptic NA via NA reuptake inhibition, and that 5‐HT_1A activation can counter the undesirable cardiovascular effects resulting from increased sympathetic activity. Selective NA reuptake inhibitors did not reduce food intake alone but did when combined with 5‐HT_1A activation. Hence increased synaptic serotonin, via serotonin reuptake inhibition or 5‐HT_1A activation, together with increased NA, would appear to produce hypophagia. Thus weight loss with minimal cardiovascular risk could be achieved by 5‐HT_1A activation combined with NA transporter blockade.     

Effects of a newly synthesized leukotriene antagonist, NZ-107, on immediate-type hypersensitivity reaction in rats and guinea-pigs.

The effects of 4-bromo-5-(3-ethoxy-4-methoxybenzylamino)-3(2H)-pyridazinone (NZ-107) on immediate type hypersensitivity reactions in rats and guinea-pigs were studied. 1. When NZ-107, at a dose of 50 mg/kg (i.p.) or 100 mg/kg (orally), was administered to rats, 48-h homologous passive cutaneous anaphylaxis (PCA) reaction and histamine-, leukotriene C4 (LTC4)- and leukotriene D4 (LTD4)-induced skin reactions were suppressed by the agent. 2. NZ-107 (10(-6) g/ml) inhibited both LTC4- and LTD4-induced contractions of isolated rat stomach smooth muscle. 3. NZ-107 inhibited antigen-induced histamine release from rat peritoneal mast cells by 26% at a concentration of 10(-4) g/ml. 4. NZ-107, at doses of 25 and 50 mg/kg (orally), significantly inhibited guinea-pig 3-h heterologous PCA reaction. 5. NZ-107 inhibited antigen-induced histamine release from guinea-pig lung tissue by 17% and 48% at concentrations of 5 x 10(-5) and 10(-4) g/ml, respectively. 6. NZ-107, at doses of 25 and 50 mg/kg (i.p.), inhibited antigen-induced bronchoconstriction and eosinophil accumulation in the bronchoalveolar lavage fluid (BALF) of guinea-pigs. These results suggest that NZ-107 has anti-allergic action including inhibition of eosinophil accumulation in an antigen-challenged airway lesion in rats and guinea-pigs. The anti-allergic action of this agent is thought to be due to its action as a histamine and LT antagonist and its consequent inhibition of antigen-induced histamine release.     

Interaction between leukotriene C4 and histamine in the guinea-pig

Lipoxygenase metabolites have proposed as potential chemical mediators of the bronchial hyperractivity which characterizes asthma (2,6). In addition to the possibility that leukotrienes (LTs) sensitize airways smooth muscle to the contractile actions of other mediators such as histamine (1–3), a number of studies have provided evidence for LT-induced enhancement of bronchoconstriction by a vagal dependent mechanism (4–6). In the present study the effects of exposure of the airway to LTC₄ on subsequent responsiveness to histamine have been investigated in both and experiments. LTC₄, in a concentration eliciting threshold contractile responses of the isolated trachea (1.7 nM), had no effect on either the EC₅₀ or maximal contractile response to histamine. At a concentration eliciting an approximately EC₅₀ contractile response, LTC₄ (10 nM) shifted the histamine concentration-response curve rightwards altering the maximum response. In anaesthetized, mechanically ventilated guinea pigs LTC₄ (0.1–0.4 nMole/kg, i.v.) injected 20 s beforehand, failed to alter histamine (9–36 nMole/kg, i.v.)-induced bronchoconstriction whereas, under the same conditions, LTD₄ (0.05–0.2 nMole/kg, i.v.) dose-dependently enhanced histamine-induced bronchoconstriction. On the other hand, LTC₄ or LTD₄ (16 uM, 30 s) aerosols potentiated histamine (9.36 nMole/kg, i.v.) in a concentration-dependent manner (Table). Both LTC₄ and LTD₄ aerosols enahance airway reactivity to histamine whereas only LTD₄ has this action when administered intravenously. Neither LTC₄ nor LTD₄ (6) enhances the contractile effects of histamine on isolated airways smooth muscle. It is concluded that the broncho-constriction enhancing action of these leukotrienes may be indirectly mediated.     

Metrifonate and dichlorvos: Effects of a single oral administration on cholinesterase activity in rat brain and blood

Cholinesterase activities in rat forebrain, erythrocytes, and plasma were assessed after a single oral administration of metrifonate or dichlorvos. In 3-month-old rats, the dichlorvos (10 mg/kg p.o.)-induced inhibition of cholinesterase reached its peak in brain after 15–45 min and after 10–30 min in erythrocytes and plasma. Cholinesterase activity recovered rapidly after the peak of inhibition, but did not reach control values in brain and erythrocytes within 24 h after drug administration. The recovery of plasma cholinesterase activity, in contrast, was already complete 12 h after dichlorvos treatment. Metrifonate (100 mg/kg p.o.) had qualitatively similar inhibition kinetics as dichlorvos, albeit with a slightly delayed onset. Peak values were attained 45–60 min (brain) and 20–45 min (blood), after drug administration. Apparently complete recovery of cholinesterase activity was noted in both tissues 24 h after treatment. The dose-dependence of drug-induced inhibition of cholinesterase in rat blood and brain was determined at the time of maximal inhibition, i.e., 30 min after dichlorvos treatment and 45 min after metrifonate treatment. The oral ED₅₀ values obtained for dichlorvos were 8 mg/kg for brain and 6 mg/kg for both erythrocyte and plasma cholinesterase. The corresponding oral ED₅₀ values for metrifonate were 10 to 15 times higher, i.e., 90 mg/kg in brain and 80 mg/kg in erythrocytes and plasma. In rats deprived of food for 18 h before drug treatment, the corresponding ED₅₀ values for metrifonate were 60 and 45 mg/kg, respectively, indicating an about two-fold higher sensitivity of fasted rats to metrifonate-induced cholinesterase inhibition compared to non-fasted rats. Compared to 3-month-old rats, 19-month-old rats showed a higher sensitivity towards metrifonate and dichlorvos. At the time of maximal inhibition, there was a strong correlation between the degree of cholinesterase inhibition in brain and blood. These results demonstrate that single oral administration of metrifonate and dichlorvos induces an inhibition of blood and brain cholinesterase in the conscious rat in a dose-dependent and apparently fully reversible manner. While the efficiency of a given dose of inhibitor may vary with the satiety status or age of the animal, the extent of brain ChE inhibition can be estimated from the level of blood ChE activity.     

Discovery of L-791,943: a potent,selective, non emetic and orally active phosphodiesterase-4 inhibitor

Structure-activity relationship studies directed toward improving the potency and metabolic stability of CDP-840 (3) resulted in the discovery of L-791,943 (11n) as a potent (HWB TNF-alpha = 0.67 microM) and orally active phosphodiesterase type 4 (PDE4) inhibitor. This compound, which bears a stable bis-difluoromethoxy catechol and a pendant hexafluorocarbinol, exhibited a long half-life in rat and in squirrel monkey. It is well tolerated in ferret with an emetic threshold greater than 30 mg/kg (po) and was found to be active in the ovalbumin-induced bronchoconstriction model in guinea pig and in the ascaris-induced bronchoconstriction models in sheep and squirrel monkey.     

Pharmacological actions of Y-24180: I. A potent and specific antagonist of platelet-activating factor

The ability of Y-24180, 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H-thieno[3,2-f][1,2,4]triazolo[4,3-a] [1,4]diazepine to inhibit platelet-activating factor (PAF)-induced reactions was investigated. Y-24180 (0.0003–0.003 mg/kg, i.v.) dose-dependently inhibited PAF-induced bronchoconstriction in guinea pigs, but even at a high dose of 10 mg/kg, i.v., it was either inactive or weakly active against the bronchoconstriction induced by histamine, serotonin, acetylcholine, arachidonic acid, bradykinin, or leukotriene D₄. Oral doses (0.003–0.1 mg/kg) of Y-24180 also prevented hemoconcentration due to PAF in a dosedependent manner and produced a parallel shift of the PAF dose-response curve. Y-24180 (0.0003–0.1 mg/kg, i.v.) and WEB 2086 (0.03–1 mg/kg, i.v.) dose-dependently reversed PAF-induced hypotension in anesthetized rats. In mice, PAF-induced lethality was inhibited by Y-24180 and WEB 2086 with ED₅₀ values of 0.022 and 1.42 mg/kg, p.o., and 0.023 and 0.12 mg/kg, i.v., respectively. This protective effect of Y-24180 given p.o. persisted for at least 6 hr. In actively sensitized mice lethal anaphylactic shock was prevented by oral doses of Y-24180 and WEB 2086 with ED₅₀ values of 0.095 and 0.69 mg/kg, respectively. These results suggested that Y-24180 is an extremely potent and specific PAF antagonist with a good duration of action.     

Inhibition of δ-aminolevulinic acid synthetase and δ-aminolevulinic acid dehydrase by L-2-amino-4-methoxy-trans-3-butenoic acid in the rat

The rate limiting enzyme of heme biosynthesis, δ-aminolevulinic acid synthetase (ALA synthetase), and the second enzyme in the heme biosynthetic pathway, δ-aminolevulinic acid dehydrase (ALA dehydrase), were inhibited by the olefinic amino acid L-2-amino-4-methoxy - $\text{trans}$-3-butenoic acid (AMTB). Administration of AMTB (20 mg/kg; i.p.) to rats inhibited ALA synthetase and ALA dehydrase in control animals and in animals with markedly elevated activity of ALA synthetase which resulted from the administration of 3,5-dicarbethoxy-1,4-dimethyl-collidine (DDC, 200 mg/kg, i.p.) or allylisopropylacetamide (200 mg/kg, s.c.). AMTB also blocked the synthesis of rat hepatic porphyrins and inhibited the increase in the urinary excretion of δ-aminolevulinic acid and porphobilinogen following DDC (150 mg/kg, p.o.) administration. Preincubation of AMTB with liver mitochondria or a soluble fraction of liver decreased the activity of mitochondrial ALA synthetase and soluble ALA dehydrase, respectively.     

The effect of an orally active leukotriene D4/E4 antagonist, LY171883, on antigen-induced airway responses in allergic sheep

Leukotriene (LT) D₄ is a putative mediator of allergic asthma: inhaled LTD₄ produces early and late increases in specific lung resistance (SR_L) and slows tracheal mucus velocity (TMV) similat to inhaled antigen. In this study we examined the effects of an orally active LTD₄/LTE₄ antagonist, LY171883 [1-<2-Hydroxy-3-propyl-4-<4-(1H-Tetra-zol-5-yl) Butoxy>Phenyl>Ethanonel], on early and late changes in SR_L and TMV following airway challenge with antigen in conscious allergic sheep. SR_L and TMV were measured before and up to 8 h and 24 h after antigen challenge after either LY171883 (30 mg/kg, p.o. 2 h before challenge) or placebo pretreatment. After placebo pretreatment antigen challenge resulted in significant early (483% over baseline) and late (221% over baseline) increases in SR_L (n=9). LY171883 pretreatment, however, significantly reduced the early increase in SR_L (163% over baseline) and blocked the late response. LY171883 did not prevent the antigen-induced fall in TMV from 5–8 h post challenge (n=6), but TMV recovered more rapidly in the drug trial returning to baseline values by 24 h. These results suggest that the generation of LTD₄, and its metabolite LTE₄, during airway anaphylaxis contributes to the early increase in SR_L and is important for eliciting the late increase in SR_L as well as contributing to the fall in TMV.     

Dopamine Agonist-Induced Inhibition of Neurotransmitter Release from the Awake Squirrel Monkey Putamen as Measured by Microdialysis

Abstract: Male squirrel monkeys ( Saimiri sciureus ) were surgically prepared with cranial guide cannulae for acute microdialysis sampling of the putamen nucleus, a dopamine (DA)-rich brain region. On the day of an experiment, an animal was placed in a Plexiglas restraining chair and a microdialysis probe was inserted through the guide into the putamen. Perfusates of artificial cerebrospinal fluid were collected every 20 min over several hours and analyzed via HPLC with electrochemical detection. DA D₂/D₃ agonist drugs were administered either orally (p.o.) or subcutaneously (s.c.), and changes in levels of DA in the dialysates were measured. All of the drugs tested, i.e., quinpirole (0.5 mg/kg p.o.), talipexole (0.75 mg/kg p.o. or s.c.), and PD 135222 (7 mg/kg p.o.), decreased spontaneous DA overflow by ∼40–50% during the first 2 h following dosing. In animals that routinely underwent the microdialysis procedure up to 23 times over a 2-year period, there was neither an appreciable change in basal DA overflow nor a significant change in the magnitude of drug response. These data suggest that DA D₂/D₃ agonists attenuate DA neuronal overflow in the primate brain, similar to effects seen in rodents. Furthermore, these results also demonstrate the utility of repeated intracerebral microdialysis as a tool to monitor dynamic changes in neurochemical activity in monkeys over a prolonged period of time.     

OKY-046 inhibits anaphylactic bronchoconstriction and reduces histamine level in bronchoalveolar lavage fluid in sensitized guinea pigs.

We investigated the effects of OKY-046, a potent and selective thromboxane A2 (TxA2) synthetase inhibitor, on anaphylactic bronchoconstriction and release of chemical mediators into airway lumen in sensitized guinea pigs in vivo. OKY-046 dose-dependently inhibited antigen-induced anaphylactic bronchoconstriction with or without mepyramine, a histamine H1 antagonist. In the presence of mepyramine, OKY-046 (300 mg/kg, p.o.) elicited significant reductions in histamine (1 min) and TxB2 increases (1-15 min) in bronchoalveolar lavage (BAL) fluid but significantly increased the plasma level of 6-keto-PGF1 alpha, a stable PGI2 metabolite, after antigen challenge. On the contrary, indomethacin only significantly reduced increases in TxB2 levels. These results suggest that the antiasthmatic effect of OKY-046 is probably due to inhibition of TxA2 synthesis and suppression of histamine release via a PGI2 shunting mechanism.