Pharmacological evaluation of selective α2c-adrenergic agonists in experimental animal models of nasal congestion.

Nasal congestion is one of the most troublesome symptoms of many upper airways diseases. We characterized the effect of selective α2c-adrenergic agonists in animal models of nasal congestion. In porcine mucosa tissue, compound A and compound B contracted nasal veins with only modest effects on arteries. In in vivo experiments, we examined the nasal decongestant dose-response characteristics, pharmacokinetic/pharmacodynamic relationship, duration of action, potential development of tolerance, and topical efficacy of α2c-adrenergic agonists. Acoustic rhinometry was used to determine nasal cavity dimensions following intranasal compound 48/80 (1%, 75 µl). In feline experiments, compound 48/80 decreased nasal cavity volume and minimum cross-sectional areas by 77% and 40%, respectively. Oral administration of compound A (0.1-3.0 mg/kg), compound B (0.3-5.0 mg/kg), and d-pseudoephedrine (0.3 and 1.0 mg/kg) produced dose-dependent decongestion. Unlike d-pseudoephedrine, compounds A and B did not alter systolic blood pressure. The plasma exposure of compound A to produce a robust decongestion (EC(80)) was 500 nM, which related well to the duration of action of approximately 4.0 hours. No tolerance to the decongestant effect of compound A (1.0 mg/kg p.o.) was observed. To study the topical efficacies of compounds A and B, the drugs were given topically 30 minutes after compound 48/80 (a therapeutic paradigm) where both agents reversed nasal congestion. Finally, nasal-decongestive activity was confirmed in the dog. We demonstrate that α2c-adrenergic agonists behave as nasal decongestants without cardiovascular actions in animal models of upper airway congestion.

Mineralocorticoid receptor antagonists attenuate pulmonary inflammation and bleomycin-evoked fibrosis in rodent models.

Accumulating evidence indicates protective actions of mineralocorticoid antagonists (MR antagonists) on cardiovascular pathology, which includes blunting vascular inflammation and myocardial fibrosis. We examined the anti-inflammatory and anti-fibrotic potential of MR antagonists in rodent respiratory models. In an ovalbumin allergic and challenged Brown Norway rat model, the total cell count in nasal lavage was 29,348 ± 5451, which was blocked by spironolactone (0.3-60 mg/kg, p.o.) and eplerenone (0.3-30 mg/kg, p.o.). We also found that MR antagonists attenuated pulmonary inflammation in the Brown Norway rat. A series of experiments were conducted to determine the actions of MR blockade in acute/chronic lung injury models. (1) Ex vivo lung slice rat experiments found that eplerenone (0.01 and 10 µM) and spironolactone (10 µM) diminished lung hydroxyproline concentrations by 55 ± 5, 122 ± 9, and 83 ± 8%. (2) In in vivo studies, MR antagonists attenuated the increases in bronchioalveolar lavage (BAL) neutrophils and macrophages caused by lung bleomycin exposure. In separate studies, bleomycin (4.0 U/kg, i.t.) increased lung levels of hydroxyproline by approximately 155%, which was blocked by spironolactone (10-60 mg/kg, p.o.). In a rat Lipopolysaccharide (LPS) model, spironolactone inhibited acute increases in BAL cytokines with moderate effects on neutrophils. Finally, we found that chronic LPS exposure significantly increased end expiratory lung and decreased lung elastance in the mouse. These functional effects of chronic LPS were improved by MR antagonists. Our results demonstrate that MR antagonists have significant pharmacological actions in the respiratory system.

Alpha-2c-adrenergic receptors contribute to basal nasal patency in the anesthetized cat.

BACKGROUND: Nasal congestion is the most troublesome symptom associated with a variety of upper airway diseases, including allergic rhinitis and the common cold. A better understanding of the mechanisms that regulate nasal cavity caliber may engender the development of novel treatment strategies. It is well accepted that alpha-adrenergic (both alpha(1) and alpha(2)) mechanisms play a fundamental role in the control and maintenance of basal nasal patency. JP-1302 is a selective alpha(2c)-subtype antagonist that has been recently described in the scientific literature. Thus, we sought to examine the potential effects of this new pharmacological tool on basal nasal patency. METHODS: Using acoustic rhinometry, we studied the activity of the selective alpha(2c)-antagonist JP-1302 on nasal cavity volumes in an anesthetized cat. Cumulative concentrations of JP-1302 were applied directly into the right nasal cavity. Changes in the nasal cavity geometry of the drug-treated naris relative to the untreated left nasal cavity were determined. In separate studies, the nonselective alpha(2)-antagonist yohimbine and the nonselective alpha(1)-antagonist prazosin were run as comparators. Systolic blood pressure was measured at the hind leg, using an ultrasonic Doppler flow detector. RESULTS: JP-1302 (0.03, 0.1, 0.3 and 1.0%) administered by the intranasal route decreased nasal cavity volumes from baseline values by 17, 25, 40 and 40%, respectively. Yohimbine (0.03, 0.1, 0.3 and 1.0%) decreased volumes by 19, 36, 46 and 53%, and topical administration of the nonselective alpha(1)-antagonist prazosin (0.001, 0.003, 0.01, 0.03 and 0.1%) decreased volumes by 6, 47, 56, 64 and 71%, respectively. JP-1302, yohimbine and prazosin, at the dose level tested, did not alter the blood pressure. CONCLUSIONS: The present set of experiments indicates that both alpha(1)- and alpha(2)-adrenergic receptors are involved in the maintenance of basal nasal patency in the cat. Moreover, alpha(2c)-receptors may play a significant role in the sympathetic control of upper airway function.

Loratadine and montelukast administered in combination produce decongestion in an experimental feline model of nasal congestion.

BACKGROUND: Histamine and leukotrienes act to exert numerous local and systemic effects that contribute to the pathophysiology of allergic rhinitis. The aim of these experiments was to evaluate the nasal decongestant effects of loratadine and montelukast alone and in combination in a feline model of nasal congestion. We also studied the decongestant actions of the alpha-agonist adrenergic agonist D-pseudoephedrine with and without desloratadine. METHODS: Acoustic rhinometry was used to determine nasal cavity dimensions after intranasal compound 48/80. Cats were given D-pseudoephedrine (0.3 mg/kg) alone or in combination with desloratadine (5 mg/kg) 1 hour before nasal provocation with compound 48/80 (1%, 75 microliters) to either the left or right nasal passageway. Using a similar design, the nasal decongestant effects of montelukast (1 mg/kg) and loratadine (10 mg/kg) were studied alone and in combination. RESULTS: The addition of desloratadine to D-pseudoephedrine did not improve decongestant efficacy compared with each drug given individually. In contrast, when montelukast (1 mg/kg) was given in combination with loratadine (10 mg/kg), the decongestant activity was greater than when these drugs were administered separately. Sixty minutes after compound 48/80 provocation the nasal cavity volume ratio (volume ratio of the compound 48/80 treated/untreated nasal passageway) for the control, montelukast alone, loratadine alone, and the montelukast plus loratadine-treated groups were 0.20 +/- 0.03, 0.24 +/- 0.01, 0.28 +/- 0.03, and 0.50 +/- 0.03. CONCLUSION: Concomitant montelukast plus loratadine produces a greater degree of nasal decongestion compared with montelukast or loratadine alone in an experimental model of nasal congestion.

Effect of combined histamine H1 and H3 receptor blockade on cutaneous microvascular permeability elicited by compound 48/80.

The pharmacological consequences of combining a histamine H1 receptor antagonist with a H3 antagonist on cutaneous microvascular permeability due to intradermal (i.d.) injections of compound 48/80, a mast cell liberator of histamine, was studied in the anesthetized guinea pig. Compound 48/80 (0.0003, 0.001, 0.003 and 0.01%) induced permeability responses were attenuated, as determined by Evans blue extravasation, in animals pretreated with the H1 antagonist, chlorpheniramine (CTM; 1.0 mg/kg, i.v.) by 17 +/- 4, 31 +/- 4, 32 +/- 4 and 37 +/- 4%, respectively. Combination treatment with an H1 and H3 antagonist displayed greater inhibitory efficacy against the effects elicited by compound 48/80. Specifically, combined treatment with CTM (1.0 mg/kg, i.v.) and the H3 antagonist, thioperamide (THIO 1.0 mg/kg,i.v.) inhibited the skin responses of i.d. compound 48/80 (0.0003, 0.001, 0.003 and 0.01%) by 36 +/- 4, 45 +/- 4, 49 +/- 4 and 54 +/- 4%. A second H3 antagonist, clobenpropit (CLOB; 0.3 mg/kg, i.v.) plus CTM (1.0 mg/kg, i.v.) also inhibited Evans blue extravasation. Treatment with THIO (1.0 mg/kg, i.v.) and CLOB (0.3 mg/kg, i.v.) administered alone had no effect on compound 48/80-induced skin responses. We conclude that combination administration of a H1 and a H3 histamine receptor antagonist produces greater inhibitory effect on cutaneous microvascular permeability produced by released mast cell-derived histamine than either a H1 or H3 antagonist administered separately. In addition, the antiallergy activity of combining a H3 antihistamine with a H3 antagonist activity might provide a novel approach for the treatment of allergic skin diseases such as urticaria.

Pharmacological characterization of the novel histamine H3-receptor antagonist N-(3,5-dichlorophenyl)-N'-[[4-(1H-imidazol-4-ylmethyl)phenyl]-methyl]-urea (SCH 79687).

We present the pharmacological and pharmacokinetic profiles of a novel histamine H3 receptor antagonist, N-(3,5-dichlorophenyl)-N'-[[4-(1H-imidazol-4-ylmethyl)phenyl]-methyl]-urea (SCH 79687). The H3-receptor binding Ki values for SCH 79687 were 1.9 and 13 nM in the rat and guinea pig (GP), respectively. The Ki values for SCH 79687 at histamine H1 and H2 receptors were greater than 1 microM. SCH 79687 showed a 41- and 82-fold binding selectivity for the H3 receptor over alpha 2A-adrenoceptors and imidazoline I2, and >500-fold H3 selectivity compared with over 60 additional receptors. The pA2 value for SCH 79687 in the GP ileum electrical field-stimulated (EFS) contraction was 9.6 +/- 0.3. Similar H3 antagonist activity was observed in the EFS cryopreserved and fresh tissue isolated human saphenous vein (HSV) assays (pKb = 9.4 +/- 0.3 and 10.1 +/- 0.4). SCH 79687 (30 nM) did not block clonidine-induced inhibition of EFS-induced contractions in HSV. SCH 79687 (ED50 = 0.3 mg/kg i.v.) attenuated (R)-alpha-methylhistamine inhibition of sympathetic hypertensive responses in the GP. At the time of activity evaluation, the GP plasma SCH 79687 concentration was 25 ng/ml at the dose of 0.3 mg/kg i.v. In feline nasal studies, combined administration of SCH 79687 (3 mg/kg i.v.) and the H1-antagonist loratadine (3 mg/kg i.v.), at individual doses that do not produce decongestion, inhibited the compound 48/80-induced congestion by 47%. The alpha-adrenergic agonist phenylpropanolamine (PPA; 1 mg/kg i.v.) also attenuated compound 48/80 nasal responses by 42%. Unlike the H3/H1 combination that did not affect blood pressure (BP), PPA (1 mg/kg i.v.) significantly increased BP compared with control animals by a maximum of 31 mm Hg. Orally, SCH 79687 (10 mg/kg) plus loratadine (10 mg/kg) also produced decongestion without effects on BP. In pharmacokinetic studies, oral dosing with SCH 79687 in the rat (10 mg/kg) and monkey (3 mg/kg) achieved plasma Cmax and area under the curve values greater than 1.5 and 12.1 microg. h/ml, respectively. SCH 79687 is an orally active H3 antagonist with a good pharmacokinetic profile that, in combination with an H1 antagonist, demonstrates decongestant efficacy comparable with oral sympathomimetic decongestants but without hypertensive liabilities.