Pulmonary pharmacology of DT-TX 30 SE, a potent selective combined thromboxane synthetase inhibitor and receptor antagonist, in guinea pigs.

A novel chemical compound, DT-TX 30 SE (E-6-(4-2-(4-chlorobenzenesulphonylamino)-ethyl)phenyl)-6-(3-pyrid yl)- hex-5-enoic acid), was studied in various models of guinea pig pulmonary function. The compound was a potent inhibitor (ED50 0.019 mg/kg, i.v.) of bronchospasm induced by the thromboxane receptor agonist U-46619, indicating thromboxane receptor antagonism. At even lower doses (ED50 0.0036 mg/kg, i.v.), it blocked arachidonic acid-induced bronchospasm. Interpretation of the latter results as evidence for additional thromboxane synthetase inhibitory activity was supported by the inhibition of arachidonic acid- or bradykinin-induced thromboxane B2 production in an isolated lung preparation, although prostaglandin E2 and prostaglandin 6-oxo-F(1 alpha) production measured at the same time were not inhibited. The potency of DT-TX 30 SE was compared with thromboxane receptor antagonists and synthetase inhibitors described in the literature. As a receptor antagonist, DT-TX 30 SE was significantly more potent than BM 13505 and BM 13177 (assessed by antagonism of U-46619-induced bronchospasm), but less potent than SQ 29548, while as a thromboxane synthetase inhibitor, it was significantly more potent than OKY 046 and UK 37248 as assessed by antagonism of arachidonic acid-induced bronchospasm or (OKY 046) inhibition of thromboxane production in isolated lung. The compound was active by the oral route as shown by its ability, at 10 mg/kg, p.o., to significantly reduce the immediate allergic response of sensitized guinea pigs to an ovalbumin aerosol.

Platelet-activating factor antagonists in experimental shock.

Platelet-activating factor (PAF) at 10 micrograms/kg i.v. induced profound hyperkalemia, changes of hematological parameters, patterns of ECG, and acid-base balance in rats. In separate experiments infusions of PAF at 30 ng/kg/min or injection of endotoxin from E. coli (15 mg/kg i.v.) induced a marked drop in blood pressure. All these changes were antagonized by pretreatment or post-treatment (in case of hypotension) by the selective hetrazepinoic PAF antagonists apafant (WEB 2086, CAS 105219-56-5; 0.1-5 mg/kg i.v.), bepafant (WEB 2170, CAS 114776-28-2; 0.05-1.0 mg/kg i.v.), or STY 2108 (0.01-0.1 mg/kg), respectively. The results support the view that PAF can mimic features of endotoxin shock and that the hetrazepines (like apafant, bepafant) are useful tools to clarify the role of PAF in such conditions.

Pharmacologic activity of bepafant (WEB 2170), a new and selective hetrazepinoic antagonist of platelet activating factor.

The hetrazepine WEB 2170 (international nonproprietary name: bepafant), a thieno-triazolodiazepine that is structurally related to the recently described platelet activating factor (PAF) antagonist WEB 2086, is a potent and selective PAF antagonist both in vitro and in vivo. WEB 2170 inhibited PAF-induced human platelet and neutrophil aggregation in vitro (IC50 values: 0.3 and 0.83 microM, respectively) but had little or no inhibitory action against aggregation induced by other agonists. The potency in vitro was comparable to that described recently for WEB 2086 (Casals-Stenzel, J., Muacevic, G. and Weber, K.H.: J. Pharmacol. Exp. Ther. 241: 974-981, 1987). When guinea pigs were given i.v. infusions of PAF at 30 ng x kg-1 x min-1, oral (0.005-0.5 mg/kg) as well as intravenous (0.005-0.05 mg/kg) treatment with WEB 2170 abrogated the intrathoracic accumulation of 111In-labeled platelets, the bronchoconstriction and the hypotension as well as the finally occurring death in a dose-dependent fashion. Oral (0.01-1 mg/kg) and intravenous (0.005-0.1 mg/kg) WEB 2170 shared with the beta 2 agonist fenoterol and the steroid dexamethasone the property of protecting elderly NMRI mice from the lethal effect of PAF. In anesthetized rats, intravenous (0.001-0.1 mg/kg) and oral (0.05-1 mg/kg) WEB 2170 inhibited PAF-induced hypotension in a dose-related manner. Coadministration of WEB 2170 inhibited PAF-induced increase of vascular permeability in rat skin very effectively. The half-time of duration of action in the rat was estimated to be about 5 to 6 h after oral administration and about 1.1 to 2.3 h after intravenous application. In conclusion, the hetrazepine WEB 2170 is a strong and selective PAF antagonist, which is in vitro more or less equipotent to WEB 2086. In contrast, in vivo oral WEB 2170 is--depending on the species and considered parameter--about 5 to 40 times more potent against exogenous PAF-induced alterations than the recently described hetrazepine WEB 2086. Particularly in mice and rats, oral WEB 2170 is by far superior to WEB 2086.

Pharmacological actions of WEB 2086, a new specific antagonist of platelet activating factor.

WEB 2086, a thieno-triazolodiazepine, is a potent and specific antagonist of platelet activating factor (PAF) in vitro and in vivo. This compound inhibits PAF-induced human platelet and neutrophil aggregation in vitro (IC50 = 0.17 and 0.36 microM, respectively) but has little or no effect on the action of other platelet aggregating agents. In comparison with kadsurenone, ketotifen or thiazinamium chloride, WEB 2086 was 26 to 200 times more potent in the PAF-induced platelet aggregation. In anesthetized guinea pigs, pretreatment with 0.1 to 2.0 mg/kg p.o. or 0.01 to 0.5 mg/kg i.v. of WEB 2086 inhibits dose-dependently the accumulation and aggregation of 111Indium labeled platelets, bronchoconstriction, systemic hypotension and also the lethal effect due to an i.v. PAF infusion [30 ng/(kg X min)] or intratracheal instillation of PAF (300 micrograms/kg). Under the same experimental conditions in guinea pigs, WEB 2086 given by inhalation achieved a similar anti-PAF activity. In anesthetized rats, the hypotension induced by an i.v. PAF infusion was also reversed (ED50 = 0.052 mg/kg i.v.). The increase in cutaneous vascular permeability due to intradermal PAF (25 ng/site) was inhibited dose-dependently by WEB 2086 (0.025-2 micrograms/site) in rats. Because of its structural relationship to triazolodiazepines, WEB 2086 was examined for anticonvulsant and sedative action. Up to doses of 300 and 800 mg/kg p.o., respectively, no effects were found. In conclusion, WEB 2086 is a potent and specific PAF antagonist with triazolodiazepine structure but without sedative activity.

Inhibitory effects of clonidine on bronchospasm induced in guinea-pigs by vagal stimulation or antigen challenge.

The effects of clonidine on the bronchospastic responses induced by vagal stimulation or antigen challenge were studied in anaesthetized guinea-pigs. Electrical stimulation of the vagus nerves by 2-4 Hz induced a vigorous, mainly atropine-sensitive bronchoconstriction, which was strongly inhibited by clonidine (0.05 mg/kg i.v.). The inhibitory effect of clonidine was significantly reduced by the alpha 2-adrenoceptor antagonist yohimbine (1 mg/kg i.v.). Another series of experiments was done with ovalbumin-sensitized guinea-pigs. Respiratory anaphylaxis was induced by antigen inhalation resulting in an increase of pulmonary resistance from 100% (baseline) to about 190% in the control group. Animals pretreated with a clonidine aerosol (0.03%) showed a marked inhibition of the bronchospastic response. It is suggested that the inhibition of the bronchospastic responses induced by clonidine may be mediated by a stimulation of alpha 2-adrenoceptors, which exerts an inhibitory control of the excitatory vagal activity in the guinea-pig airways.

Reversible pulmonary changes in rats dosed intravenously with imidazoles.

Pulmonary changes were studied in Sprague-Dawley-rats dosed intravenously with various dosages around the LD 50 in acute studies, and with 0 (control), 0.001, 0.01 and 0.1 mg/kg b. wt./day St 91-Cl or with 0, 1, 5 and 25 mg/kg b. wt./day St 600-Cl for 4 weeks in subacute studies. Doses of 0.01 mg/kg St 91-Cl and 1 mg/kg St 600-Cl were well tolerated. At higher doses, both compounds caused acute pulmonary congestion, edema and bleeding. The acute changes obviously occurred after each single i.v. injection, and were followed by an intensive hemosiderosis of alveolar macrophages. All findings were reversible. No pulmonary changes were observed in oral subacute studies with both compounds.

Pharmacological effects of a combination of fenoterol hydrobromide and ipratropium bromide.

The bronchospasmolytic and cardiovascular effects of fenoterol hydrobromide and ipratropium bromide alone and in combination were investigated using metered aerosols in guinea pigs and dogs and intravenous injection in dogs. The additive effect of the combination on bronchospasmolysis could be demonstrated. The slight cardiovascular side-effects of fenoterol hydrobromide alone were reduced to an insignificant level with the combination administered as a metered aerosol, but were still present when the combination was administered parenterally. Ipratropium bromide in both forms of administration had no effect on the cardiovascular system.

Determination of bioavailability on the basis of tachycardia after intravenous and oral administration of fenoterol, orciprenaline and salbutamol in non-anaesthetized rats.

Three beta-sympathomimetics, fenoterol, orciprenaline and salbutamol, were tested for their tachycardia effect in conscious rats sedated with brotizolam. The tachycardia after oral and intravenous administration and the time-effect curves were used for the determination of the bioavailability. In these experiments, fenoterol and orciprenaline showed better bioavailability than salbutamol. The tachycardic time effects of fenoterol and orciprenaline were of shorter duration than that of salbutamol.

Pharmacological effects and determination of the morphological distribution of powder aerosols containing fenoterol hydrobromide and ipratropium bromide.

The bronchospasmolytic effects of fenoterol hydrobromide and ipratropium bromide, with some cardiovascular side effects by fenoterol, and the topographic morphological distribution of the powder aerosol particles in the respiratory tract were clearly demonstrated with the aid of ethidium-induced fluorescence in anaesthetised dogs.

Detection of aerosols in the respiratory tract.

A fluorescence method for the detection of inhaled aerosols in the respiratory tract has been described. The most suitable fluorescence indicator for the histological examination was ethidium bromide.

New apparatus and method for the toxicological investigation of metered aerosols in rats.

A new apparatus and method for the toxicological investigation of metered aerosols in rats, which is also suitable for tests in other small laboratory animals, is described. It permits: 1. simultaneous treatment of 5 or more animals, 2. administration of metered aerosol doses to individual animals, 3. ventilation of the cages, 4. mechanical tilting of the metered aerosol packs to ensure thorough mixing of the content, and 5. continuous automatic tilting, administration and ventilatied under different ventilation conditions. Blood gases and fluorinated chlorohydrocarbons (abbreviation: fluorocarbons) in the arterial blood were also determined. In tests with spontaneous ventilation of the animal chambers without positive pressure, significant acidosis and hypoxia occurred after 40 puffs of metered aerosol. Where ventilation of the chambers was insufficient, the fluorocarbons led to dose-dependent toxic and lethal effects. The substance and the additives contained in the metered aerosol did not interfere with these effects. After active ventilation with 0.5 atm no symptoms of acidosis or hypoxia were observed. Up to 160 puffs of metered aerosol, no indications of toxic effects were established in the rats. Half-life of the fluorocarbons in the arterial blood after one puff of metered aerosol was 69 to 80 sec for fluorocarbon 11 and 57 to 67 sec for fluorocarbon 12.