Pharmacological comparison of peristaltic effects in rats and mice.

INTRODUCTION: Conscious rodent models are commonly used to assess the effects of new chemical entities on propulsion (transit) time in the gastrointestinal system. This study was designed to compare three compounds clinically known to cause constipative (morphine sulfate and propantheline bromide) and laxative (metoclopramide hydrochloride) effects on transit time in rats and mice and to note if there are differences between the species. METHODS: Compounds were dosed in conscious rats and mice. At 0.5-2.0h post dosing (estimated time to maximal plasma concentration of each compound) animals were gavaged with an appropriate volume (based on weight) of 10% activated powdered carbon suspended in 5% gum arabic. Forty-five minutes following dosing the animals were sacrificed by CO2 asphyxiation and the small intestine was removed. The position of the leading edge of the charcoal was measured relative to the total length of the intestinal segment. RESULTS: The compounds tested produced variable statistical differences in transit time between species. Morphine and propantheline produced dose-dependent increases in transit time, and metoclopramide decreased transit time, statistically significant in both rodent models. DISCUSSION: The present data demonstrate that at similar doses rats and mice can be used interchangeably for transit studies. Mice were more sensitive to transit changes at higher doses of the compounds tested.

3,5-Bis(trifluoromethyl)pyrazoles: a novel class of NFAT transcription factor regulator.

A series of bis(trifluoromethyl)pyrazoles (BTPs) has been found to be a novel inhibitor of cytokine production. Identified initially as inhibitors of IL-2 synthesis, the BTPs have been optimized in this regard and even inhibit IL-2 production with a 10-fold enhancement over cyclosporine in an ex vivo assay. Additionally, the BTPs show inhibition of IL-4, IL-5, IL-8, and eotaxin production. Unlike the IL-2 inhibitors, cyclosporine and FK506, the BTPs do not directly inhibit the dephosphorylation of NFAT by calcineurin.

The role of platelet-activating factor (PAF) and the efficacy of ABT-491, a highly potent and selective PAF antagonist, in experimental allergic rhinitis.

Platelet-activating factor (PAF) may be an important mediator of allergic rhinitis. In the present study we evaluated the effectiveness of a recently described PAF antagonist (ABT-491) in rat and guinea pig models of allergic rhinitis. PAF, when perfused through the nasal passages of anesthetized Brown Norway rats, provoked an acute increase, measured as dye leakage, in nasal vascular permeability evident within 15 min after exposure to PAF. ABT-491, given orally 1 hr before PAF challenge, inhibited the response in a dose-related manner (ED50 = 0.3 mg/kg). Intranasal perfusion with ovalbumin in rats sensitized to the antigen 18 to 21 days before challenge also induced an increase in vascular permeability. The antigen-induced leakage was inhibited a maximum of 74% (P < or = .001) by pretreatment with ABT-491 (3 mg/kg p.o.). An antihistamine (mepyramine, 10 mg/kg i.p.), a serotonin antagonist (methysergide) and a 5-lipoxygenase inhibitor (A-79175) also exhibited efficacy in this model (56%, 87% and 65% inhibition, respectively). Nearly complete inhibition (93%, P < or = .001) of the response was achieved by coadministration of ABT-491 and methysergide. In guinea pigs intranasal administration of PAF resulted in increased airway resistance that was inhibited in a dose-dependent manner by oral administration of ABT-491 (ED50 = 1 mg/kg). Antigen-induced nasal airway resistance, triggered by exposure of sensitized animals to aerosolized ovalbumin, was also inhibited by ABT-491 (maximum inhibition 64%, P < or = .05, 10 mg/kg p.o.). The effectiveness of the antagonist was increased to 80% protection by coadministration with either an antihistamine or a 5-lipoxygenase inhibitor, agents which were separately insignificant in blocking the response to antigen. These results suggest a therapeutic utility for ABT-491, perhaps in combination with other anti-inflammatory agents, in the treatment of allergic rhinitis.

ABT-761 attenuates bronchoconstriction and pulmonary inflammation in rodents.

Our primary goal has been to discover leukotriene biosynthesis inhibitors with characteristics that are appropriate for use as clinical agents. The success of the use of zileuton in the treatment of asthma led us to explore further the use of the N-hydroxyurea class of 5-lipoxygenase inhibitors as longer-acting compounds with good lung penetration. A variety of in vitro and in vivo methods were used to evaluate a large number of compounds, from which ABT-761 [(R)-N-(3-(5-(4-fluorophenylmethyl)thien-2-yl)-1-methyl-2-pr opynyl)-N-hydroxyurea] was selected for study. ABT-761 exhibited potent and selective inhibition of leukotriene formation both in vitro and in vivo. More importantly, the compound potently inhibited antigen-induced bronchospasm in guinea pigs when given either prophylactically or therapeutically. In addition, ABT-761 was a potent inhibitor of eosinophil influx into the lungs of Brown Norway rats. These data provide added support for the role of leukotrienes in both bronchospasm and eosinophilic inflammation and characterize ABT-761 as a particularly potent inhibitor of leukotrienes formed in pulmonary tissues. These data combined with the excellent pharmacokinetic characteristics of the compound indicate its potential use in the treatment of leukotriene-dependent human disease.

The 5-lipoxygenase inhibitory activity of zileuton in in vitro and in vivo models of antigen-induced airway anaphylaxis.

Leukotrienes are biologically active lipid mediators capable of producing airway inflammation, hyperresponsiveness and bronchoconstriction. The first enzyme in the metabolic pathway of arachidonic acid leading to the leukotrienes is 5-lipoxygenase (5-LO). A selective and potent 5-LO inhibitor, zileuton (N-1(1-benzo[b]thien-2-ylethyl)-N-hydroxyurea, A-64077) was evaluated in models of airway anaphylaxis, where leukotrienes are a major component. In vitro, zileuton inhibited antigen-induced contractions of guinea-pig tracheal strips (GPTS) from actively sensitized animals with an IC50 of 6 microM. Similar results were obtained in human bronchial strips passively sensitized to IgE. Zileuton had little or no effect on contractions elicited by acetylcholine, prostaglandin D2 (PGD2), or the thromboxane agonist, U-44069. In anesthetized sensitized guinea-pigs pretreated with meclofenamic acid and mepyramine, a single aerosol exposure of antigen produced a substantial decrease in dynamic lung compliance (Cdyn). These profound changes in lung function were dose-dependently inhibited by orally administered zileuton (ED50 = 12 mg/kg). These results demonstrate that zileuton is a potent, selective inhibitor of in vitro contraction of GPTS and antigen-induced bronchoconstriction in vivo. These data also confirm the participation of 5-LO products in these models of airway anaphylaxis and suggest the usefulness of the guinea-pig for identifying and characterizing the pulmonary effects of 5-LO inhibitors.

Theophylline produces over-additive relaxation of canine tracheal smooth muscle when combined with beta-agonists: the dose-response relationship.

The interaction between theophylline (T) and the beta-agonists albuterol (A) and isoproterenol (I) was examined using canine cervical tracheal smooth muscle devoid of epithelium contracted with 0.1 or 0.3 microM methacholine. Greater functional antagonism with beta-agonists vs. T was confirmed and an ability of T to potentiate beta-agonist relaxation was demonstrated. The EC50 for T increased from 0.13 +/- 0.02 to 0.37 +/- 0.07 mM (mean +/- SEM) in preparations contracted with 0.1 or 0.3 microM methacholine, respectively, while that for I increased from 0.036 +/- 0.008 to 0.17 +/- 0.03 microM, a significantly larger change (P < 0.025). In tissues contracted with 0.3 microM methacholine and pretreated with 10 micrograms/ml of T IC50 values from composite concentration-response curves for I and A were displaced to the left and Emax was increased (56.6 to 71.5% for I, 44 to 61% for A, P < 0.0002). Addition of 10 micrograms/ml T resulted in relaxations which exceeded that calculated by the fractional product method for additive, independent action (P < 0.0001 for I, P < 0.0002 for A at 0.3 microM methacholine), suggesting that at least part of T's action was over-additive. Five, 10 and 20 micrograms/ml T enhanced the effectiveness of single concentrations of I by factors of 1.47 +/- 0.14 (P < 0.05), 2.72 +/- 0.26 (P < 0.01) and 5.34 +/- 0.55 (P < 0.01), respectively, in preparations contracted with 0.1 microM methacholine: I enhanced the effectiveness to a lesser degree. Using two approaches, positive interaction or over-additivity between T and beta-agonists has been demonstrated.

In vivo functional antagonism between isoproterenol and bronchoconstrictants in the dog.

The functional antagonism between isoproterenol and methacholine, histamine and serotonin, as described in vitro in respiratory smooth muscle was explored in vivo in a canine model. Infusions of isoproterenol were administered during brief peaks of bronchospasm produced by aerosolized methacholine and histamine, or during sustained bronchospasm produced by infused serotonin. In eight mongrel dogs anesthetized with pentobarbital sodium, the mean protection by infused isoproterenol against methacholine challenge decreased from 60.6 to 29.1% as the mean lung resistance (RL) was increased from 78 to 232% over base line by a fourfold increase in methacholine (P less than 0.002). In six dogs, the mean protection by isoproterenol against histamine decreased from 55.5 to 26.9% as the opposing RL increased from 80 to 182% over base line with a fourfold increase in histamine (P less than 0.02). However, with serotonin infusions there was only a small 18% mean decrease in protection (P = 0.05), associated with a correspondingly small 37% mean increase in dose of serotonin despite a 269% mean increase in resistance (P = 0.02). In all cases, the loss of protection correlated more closely with the dose of constrictant than the resistance increase over base line. These findings demonstrate in vivo functional antagonism between isoproterenol and the dose of bronchoconstrictant but not necessarily resistance increase per se.

Comparison of tremor responses to orally administered albuterol and terbutaline.

This study was designed to compare the initial tremor response to 4.0 mg albuterol and 5.0 mg terbutaline orally administered and to study the question of tachyphylaxis by rechallenge after 3 wk of maintenance dosing. Twenty fasting patients with severe COPD in whom orally administered sympathomimetics were withheld for 2 wk were challenged with single doses of each drug in a crossover, randomized fashion 1 wk apart. Then after a further 3 wk of dosing 3 times a day of the second medication (10 patients received each medication), they were challenged once more 16 h after the last dose. Rest and postural tremor were measured at zero and 2 h using an accelerometer affixed to the finger, and measurements of subjective tremor, tremor power spectrum, plasma cyclic AMP and lactate, and forced vital capacity were also made. Postural tremor increased from 25.05 to 36.20 relative units for albuterol, an increase of 11.15 units, and from 24.90 to 57.70 units for terbutaline, an increase of 32.80 units (difference significant at p = 0.01). Plasma cyclic AMP (p less than 0.01) and lactate (p = 0.05) increases were also less for albuterol, and the FEV1 and FVC responses, though about one third less, did not differ significantly. After 3 wk, mean baseline tremor for both drugs was elevated even 16 h after the last 3 times a day dosing (38.00 and 33.10) for albuterol and terbutaline (difference, NS), and responses were much less to the single tablet (3.40 and 9.10, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)