Interaction of azimilide with neurohumoral and channel receptors.

Binding of the class III antiarrhythmic agent azimilide to brain, heart, and other organ receptors was assessed by standard radioligand binding techniques. In a survey of 60 receptors, azimilide at 10 microM inhibited binding by more than 50% at serotonin uptake (K(i): 0.6 microM), muscarinic (K(i): 0.9 to -3.0 microM), Na(+) channel site 2 (K(i): 4.3 microM), and central sigma (K(i): 6.2 microM) sites. Lesser (20-40%) inhibition was seen at adrenergic, histamine, serotonin, purinergic, angiotensin II, dopamine uptake, and norepinephrine sites and at a voltage-sensitive K(+) channel. In rat ventricle, azimilide inhibited binding to alpha(1)- and beta-adrenergic and muscarinic receptors (K(i): < 5 microM) and to the L-type Ca(2+) channel (K(i): 37.3 microM). In rat brain, azimilide blocked ligand binding to these same receptors and to a serotonin receptor, and the breadth and potency of its interaction pattern differentiated it from ten other class III antiarrhythmics. Azimilide displayed agonist and antagonist action at five muscarinic receptor subtypes in transfected NIH 3T3 cells producing receptor-sensitive mitogenesis and beta-galactosidase activity. Agonist action predominated at M(2) and M(4) subtypes, and antagonist action predominated at M(1), M(3), and M(5) subtypes. The azimilide concentration for 50% maximum stimulation (EC(50)) in M(2)-expressing cells was 1.97 microM (vs 0.14 microM for carbachol). Azimilide's receptor interactions occur at concentrations from one to forty times those required to block cardiac delayed-rectifier channels but could contribute to the efficacy and safety of the drug.

Characterization of the anticonvulsant properties of F-721.

The anticonvulsant properties of F-721 (3-diethylamino-2,2-dimethylpropyl-5-[p-trifluoromethylphenyl]-2-f uroate hydrochloride) were investigated in a battery of in vivo and in vitro anticonvulsant model systems. After intraperitoneal (ip) administration in mice, F-721 was effective in nontoxic doses against maximal electroshock (MES), subcutaneous picrotoxin clonic, intracerebroventricular (icv) N-methyl-D-aspartate (NMDA) tonic, icv NMDA clonic and icv quisqualic acid tonic seizures (ED50s: 11.1, 28.4, 1.76, 3.4, and 4.4 mg/kg, respectively). F-721 exhibited only partial activity against clonic seizures induced in the subcutaneous Metrazol and subcutaneous bicuculline test in mice and was inactive in this species against tonic seizures induced in the subcutaneous strychnine test. F-721 was effective against MES seizures following oral administration to mice (ED50: 31.3 mg/kg) and only partially effective by this route against clonic seizures induced by subcutaneous Metrazol. In rats, F-721 was a potent anticonvulsant in the maximal electroshock model following oral administration (ED50: 9.9 mg/kg). F-721 was also effective against corneal-kindled and amygdaloid-kindled seizures in rats. F-721 suppressed stage 5 seizures in corneal-kindled rats with an ED50 of 15 mg/kg, ip. In addition, it also decreased the afterdischarge duration and behavioral seizure stage in amygdaloid-kindled rats at doses that did not cause sedation or ataxia. At 40 mg/kg, F-721 reduced afterdischarge duration by 83.2% and reduced the seizure severity score to 1.7. The ED50 for 50% reduction of afterdischarge duration was 16.3 mg/kg, ip. In cultured mouse spinal cord neurons, F-721 suppressed sustained repetitive firing in response to a depolarizing current with a median inhibitory concentration (IC50) of 1.9 microM. F-721 had no effect on adenosine uptake, gamma-aminobutyric acid or NMDA receptor binding. Comparative data from previous studies with clinically established antiepileptic agents reveal that F-721's profile of activity most closely resembles that of phenytoin and carbamazepine. However, F-721 was notably more efficacious in suppressing amygdaloid-kindled seizures in rats and was a more potent antagonist of icv NMDA clonic seizures. Our studies indicate that F-721 is a potent, orally active anticonvulsant with a favorable margin of safety. The profile of anticonvulsant activity of F-721 suggests potential utility in the management of generalized tonic-clonic, simple and complex partial seizures.

Gastric toxicity and prostaglandin content in rats dosed with two chemically similar, nonsteroidal anti-inflammatory agents.

Two chemically similar nonsteroidal anti-inflammatory drugs, orpanoxin and F-1067, had almost identical potencies and efficacies as anti-inflammatory (rat paw edema) and analgesic (mouse writhing) agents, but differed markedly in gastrotoxicity. Orpanoxin alone aggravated stomach lesions in rats subjected to pylorus ligation and failed to protect stomachs of rats challenged with indomethacin. The compounds did not differ in their in vitro enzyme inhibition effects, both failing to inhibit 5- and 15-lipoxygenase and both inhibiting prostaglandin synthetase. Extraction of prostaglandins from the gastric mucosa of pylorus-ligated rats revealed, however, that the safer F-1067 depleted prostaglandin 6-keto-F1 alpha less and increased prostaglandin E2 much more than did orpanoxin. A possible causality is suggested.

Canine carrageenin-induced acute paw inflammation model and its response to nonsteroidal antiinflammatory drugs.

A quantitative method for testing antiinflammatory agents in beagles has been developed, based on measurement of paw inflammation induced by a local injection of carrageenin. Carrageenin [0.5 mL of 2% (wt/vol) in saline] was injected into the plantar region of the hindpaws of pentobarbital-anesthetized beagles. Paw pressure changes registered from a water-filled balloon held on the top of the paw by a light adhesive tape wrapping were monitored for 240 min. In control dogs given 0.5% (wt/vol) methylcellulose (10 mL/kg orally) just before carrageenin, paw pressure increased significantly (p less than 0.05) over eightfold, from 2.9 +/- 0.8 mm Hg (mean +/- SEM, n = 29 paws) at 75 min to 26.0 +/- 3.5 mmHg at 240 min. The increase in paw pressure was significantly inhibited by the cyclooxygenase inhibitors, ibuprofen, indomethacin, and orpanoxin, and partially inhibited by the lipoxygenase inhibitor, phenidone, administered orally before carrageenin injection. Thus this model, with further characterization, could provide a convenient, quantitative way of assessing the efficacy of nonsteroidal antiinflammatory agents in dogs.

Characterization of 5-[5-(4-chlorophenyl-2-furanyl)]dihydro-2(3H)-furanone as a nonsteroidal antiinflammatory drug.

5-[5-(4-Chlorophenyl-2-furanyl)]dihydro-2(3H)-furanone (F-1044), a nonsteroidal antiinflammatory drug related to orpanoxin, lacks the usual acid moiety of such agents. F-1044 had antiinflammatory activity equivalent to ibuprofen's and orpanoxin's in the carrageenin-induced paw edema model in normal and adrenalectomized rats. Antiinflammatory activity was also expressed in the guinea pig UV-induced erythema and rat established arthritis models. F-1044 was a more potent analgesic than ibuprofen and orpanoxin in the rat paw pressure assay. In contrast to the reference agents, F-1044 raised the pain threshold of both the yeast-injected and non-injected paws, suggesting a central component to its analgesic action. F-1044 was more potent than ibuprofen and orpanoxin in the rat brewer's yeast pyresis model. Based on its low activity in inhibiting bradykinin-induced bronchoconstriction in guinea pigs and low gastric irritation activity in rats. F-1044 appears to have a mechanisms of action that involves more than simple inhibition of prostaglandin synthesis. Thus F-1044 is a nonsteroidal antiinflammatory agent with unique chemical and pharmacological features.

Effect of dantrolene sodium on [3H]nitrendipine binding to rat cardiac plasma membranes.

Dantrolene sodium (Dantrium) has antiarrhythmic activity in addition to its direct-acting skeletal muscle relaxant activity. Dantrolene sodium exerts its skeletal muscle relaxant action by reducing Ca2+ release for sarcoplasmic reticulum. The mechanism by which dantrolene sodium produces its antiarrhythmic effects is not well defined. The effects of dantrolene sodium on [3H]nitrendipine binding to rat cardiac plasma membranes were, therefore, investigated to determine whether the antiarrhythmic action involves an interaction with calcium channels. Whereas 1,4-dihydropyridines maximally inhibited [3H]nitrendipine binding with IC50 values less than 1 nM, verapamil and gallopamil (D 600) inhibited the binding not more than 70% with IC50 values at microM concentrations. Dantrolene sodium caused only minimal inhibition at concentrations up to 100 microM. Thus, the antiarrhythmic action of the drug probably involves a mechanism(s) other than an interaction with the nitrendipine binding site of the slow inward calcium channel.

Correlation between anti-hypertensive activity in rats and plasma angiotensin I-converting enzyme (ACE) inhibition in mice following oral administration of ACE inhibitors.

Thirty-four ACE inhibitors were evaluated to determine the concentration giving 50% inhibition of purified rabbit lung ACE (IC50 microM) using benzyloxycarboxyl-p-NO2-Phe-His-Leu as substrate, to determine the oral dose causing a lowering in blood pressure of 30 mm Hg (ED30 mumol/kg) in acute aortic coarctate (AAC) rats, and to determine inhibition of plasma ACE (PACE) activity in mice after oral dosing. Mouse PACE activity was determined with 14C-Hip-His-Leu as substrate one hour after oral dosing of 3 animals/group with 5 or 50 mumol ACE inhibitor per kg. Data from mice were expressed as percent of control group PACE activity. Least squares regression analysis showed the IC50 data to be poorly correlated with either rat data or mouse PACE data at 50 mumol/kg p.o. However, correlation was significant between log rat ED30 and mouse PACE at 5 (p less than 0.001, r = 0.570) and 50 (p less than 0.025, r = 0.387) mumol/kg p.o. Thus, the simple mouse plasma ACE determination after a dose of 5 mumol/kg is a convenient supplement to the AAC rat model for showing oral activity of ACE inhibitors.

Prediction of human analgesic dosages of nonsteroidal anti-inflammatory drugs (NSAIDs) from analgesic ED50 values in mice.

The oral analgesic activities (ED50's) of 15 NSAIDs were determined in the phenylquinone-induced writhing test in mice. ED50 values (mg/kg) were: acetylsalicylic acid (182), fenclofenac (168), phenylbutazone (129), ibuprofen (82.2), diflunisal (55.6), benoxaprofen (25.4), naproxen (24.1), mefenamic acid (20.7), indomethacin (19.0), meclofenamate sodium (9.60), sulindac (7.20), fenoprofen calcium (3.70), tolmetin (1.30), zomepirac sodium (0.70), and piroxicam (0.44). Significant linear correlations were found between mouse ED50 values and the various recommended human analgesic or anti-inflammatory dosages. Thus, analgesic ED50 values (mg/kg p.o.) in mice (X) may be used to predict human dosages (Y) of NSAIDs according to the equation Y = 8.26X + 535, where Y is the projected human daily dosage (mg).

5-phenyl-2-furamidines: a new chemical class of potential antidepressants.

A series of 5-phenyl-2-furamidines has been synthesized and evaluated for antidepressant activities. Substitution in the phenyl ring with a nitro (4) or an amino (12) group in the ortho-position resulted in an increase in antidepressant activity. Both 4 and 12 antagonized tetrabenazine-induced ptosis in rodents and inhibited norepinephrine (noradrenaline) uptake into crude synaptosomes of whole mouse brain at doses or concentrations comparable to those of the tricyclic antidepressants. However, these compounds did not possess the anticholinergic and antihistaminic activities common to tricyclic antidepressants. In addition, they lacked monoamine oxidase inhibitory activity. The 5-phenyl-2-furamidines represent a new chemical class of antidepressants and may be useful for depressive patients who cannot tolerate the compromising side effects of the tricyclic antidepressants and monoamine oxidase inhibitors.

Pharmacology of 1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone, a novel antidepressant compound with antianxiety activity.

1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone (I) was evaluated in selected pharmacological tests, and its activity was compared to that of some clinically useful psychotropic drugs. Based on the results, it is evident that I has a unique profile of antidepressant and antianxiety activities that are evident in the same dose range. The mechanism of its antidepressant activity is proposed to be similar to the tricyclic antidepressants, that is, inhibition of norepinephrine uptake. Neither I nor the tricyclic antidepressants possess monoamine oxidase-inhibiting activity. However, unlike the tricyclic antidepressants, I is devoid of any significant anticholinergic activity and presumably is free of anticholinergic side effects.

Synthesis and antidepressant activity of 5-(4-dimethylaminobenzyl)imidazolidine-2,4-dione.

5-(4-Dimethylaminobenzyl)imidazolidine-2,4-dione was prepared by catalytic hydrogenation of the corresponding benzylidene compound. Antidepressant testing in mice indicated that its ED50 values for antagonism of tetrabenazine-induced ptosis and potentiation of levodopa-induced behavioral changes were 42 and 17 mg/kg po, respectively. In vitro neurochemical studies demonstrated that this compound did not inhibit the uptake of selected biogenic amines into crude synaptosomes of mouse whole brain, and it did not have significant monoamine oxidase inhibitory activity in vivo and vitro. Thus, this compound possesses potential antidepressant activity with a mechanism different from that of the tricyclic antidepressants and monoamine oxidase inhibitors.

A relatively simple differential screening test for GABA or glycine antagonists using rat electroretinography.

Intravitreal injection of GABA- and glycine-antagonists had specific and reversible effects on the ERG of rats. For example, picrotoxin induced characteristic rhythmic potentials. The effect was common to other GABA-antagonists, such as bicuculline, N-methylbicuculline and penicillin G. Strychnine caused the appearance of a- and c-like waves in response to low intensity flash stimuli in addition to the suppression of the b-wave commonly seen with agents such as asparate following higher intensity flash stimuli. The strychnine-like effect was common to other glycine-antagonist tested, such as brucine, morphine and laudanosine. The quanternization of the glycine-antagonists abolished the strychnine-like activity and endowed the ability to induce the rhythmic potentials characteristic of GABA-antagonists. This relatively simple method of observing either rhythmic potentials or a negative deflection (a-like wave) to a low intensity stimulus (about 1.0 log unit above dark threshold) in the ERG should be useful for the rapid screening of the predicted and new GABA--and glycine-antagonists.