Angiotensin I-converting enzyme (ACE) inhibition and antihypertensive effects of EU-5476, a new,potent, and long-acting ACE inhibitor

EU-5476 is a new, orally active angiotensin I-converting enzyme (ACE) inhibitor. In vitro, EU-5476 produced a concentration-dependent inhibition of ACE purified from rabbit lung (IC₅₀ = 0.084 μ). Inhibition showed complex kinetics and was reversible as determined by equilibrium dialysis. EU-5476 inhibited plasma ACE in mice (93.8% inhibition at 5 μmol/kg) and produced dose-dependent inhibition of plasma ACE in dogs (ID₅₀ = 2.52 μmol/kg) after oral administration. In acute aortic coarctate hypertensive rats, EU-5476 administered orally produced dose-dependent decreases in blood pressure (ED₃₀ = 0.53 μmol/kg). The magnitude and duration of blood pressure reduction in hypertensive rats were similar to those of plasma ACE inhibition in dogs, suggesting that plasma ACE inhibition per se is one of the mechanisms of the antipertensive action of EU-5476. Comparative studies showed that EU-5476, like enalapril, was more potent and longer acting than captopril in producing plasma ACE inhibition and an antihypertensive response. EU-5476 is a potent and long-acting, orally effective ACE inhibitor potentially useful in the treatment of hypertension.     

EP1 receptor antagonist blocks the diarrheagenic,but not cytoprotective,actions of a synthetic prostaglandin

Naturally occurring and synthetic prostaglandins acting at EP type receptors have a number of physiological actions, including cytoprotective and antisecretory effects, that are therapeutically useful. In addition they can produce other effects, such as diarrhea. It is possible that these actions are mediated by different EP receptor subtypes. The actions of a subtype-selective prostaglandin agonist has suggested that diarrhea is not due to activity at the EP3 receptor, while cytoprotection and antisecretory actions may be. The recent development of a bioavailable EP1 antagonist, SC-51089, has made it possible to examine this more directly. SC-30249, the active isomer of misoprostol, protects against indomethacin-induced gastric lesions and produces diarrhea in rats. SC-51089, ig, shifted the dose-response curve for SC-30249-induced diarrhea significantly to the right. ED₅₀ values (assessed at 5 hr following administration of SC-30249) were 13.8 μ/kg (0.036 μmol/kg) for SC-30249 alone and 110.8 μg/kg (0.290 μmol/kg) for SC-30249 plus SC-51089. This antagonism of diarrhea was overcome by higher doses of SC-30249. SC-30249 dosedependently inhibited gastric lesions induced by indomethacin (ED₅₀ = 3.4 μg/kg, 0.009 μmol/kg, ig). SC-51089 did not reduce the cytoprotective effects of SC-30249 (ED₅₀ = 1.1 μg/kg, 0.003 μmol/kg, ig, SC-30249 in combination with SC-51089). These results are consistent with the hypothesis that the EP1 receptor subtype mediates the diarrheagenic effect of EP receptor agonists, but not their cytoprotective actions. These results provide a mechanistic basis for cytoprotective prostaglandins with greatly reduced side effects. © Wiley-Liss, Inc.     

Antinociceptive effects of a novel dual cyclooxygenase/5-lipoxygenase inhibitor (tepoxalin) and its primary (carboxylic acid) metabolite (RWJ 20142) in acute tests in mice and rats

Tepoxalin is a novel dual inhibitor of cyclooxygenase (CO) and lipoxygenase (LO) pathways of arachidonic acid metabolism with a relative lack of gastrointestinal side effects within its preclinical therapeutic dose range. The present study investigated the antinociceptive action of tepoxalin and its primary (carboxylic acid) metabolite (RWJ 20142) in several acute tests in mice and rats. Tepoxalin produced dose-related, non-opioid (i.e., naloxone-insensitive) antinociception in the mouse acetylcholine (ACh) induced abdominal irritant test (AIT) with an onset within 15 min and an exceptional duration (about 12 h). The oral ED₅₀ value at peak effect (30 min) was 0.3 mg/kg (0.8 μmol/kg), compared to 0.9, 38.0, and 164 mg/kg (2.5, 160.8, and 1, 085 μmol/kg), respectively, for indomethacin, zileuton, and acetaminophen. Tepoxalin was inactive via intracerebroventricular (i.c.v.) administration (up to 200μg) or (up to 100mg/kg [259 μg/kg] p.o. or s.c.) in the endothelin-1 (ET-1) AIT and mouse 48°C hot-plate tests. RWJ 20142 (a CO inhibitor), produced dose-related, non-opioid antinociception in the ACh test following oral (ED₅₀ = 0.3 mg/kg [0.8 μmol/kg] at 30 min) or i.c.v. administration (ED₅₀ = 3.3 μg [0.1 μmol] at 15 min) and was active p.o. in the phenyl-p -quinone (PpQ) (ED₅₀ = 0.2 mg/kg [0.6 μmol/kg] at 30 min) and ET-1 tests (ED₅₀ = 19.6 mg/kg [54.9 μmol/kg] at 30 min). It was the only compound active p.o. in the 48°C hot-plate test and was significantly more potent than tepoxalin in the rat air-induced AIT. Measurement of plasma levels suggests RWJ 20142 might be a major contributor to tepoxalin-induced antinociception. The inactivity of tepoxalin in the ET-1 test suggests a separate antinociceptive action of the parent compound. In summary, it appears that both tepoxalin and its primary metabolite contribute to tepoxalin-induced antinociception in rodents, possibly by different mechanisms or at different sites, i.e., peripheral vs. central. © 1995 Wiley-Liss, Inc.     

Receptor binding profile and anxiolytic-type activity of deramciclane (EGIS-3886) in animal models

The present series of experiments was done to characterize the properties of deramciclane, a new antiserotonergic drug, in both receptor binding studies in vitro and in a number of anxiolytic, antidepressant, and antidopaminergic tests in rodents. A striking property of deramciclane was its high affinity to both 5-HT_2A and 5-HT_2C receptors (K_i = 8.7–27 nM/l). Deramciclane had also a moderate affinity to dopamine D₂ and sigma receptors but did not interact with any of the adrenergic receptors. Deramciclane was active in several animal models predicting anxiolytic efficacy in humans. The active dose range of deramciclane was narrow in some tests, but generally the active dose range extended from 0.5 mg/kg (1.2 μmol/kg) to 10 mg/kg (23.9 μmol/kg). Statistically significant results were obtained in Vogel's test (1 mg/kg; 2.4 μmol/kg), social interaction (0.7 mg/kg; 1.7 μmol/kg), two-compartment box (3 mg/kg; 7.2 μmol/kg), and marble-burying tests (10 mg/kg; 23.9 μmol/kg). Although deramciclane as such was not active in the elevated plus maze, it antagonized the anxiogenic effect of the CCK agonist caerulein in this test, although significantly only at one dose (0.5 mg/kg; 1.2 μmol/kg). Deramciclane (1.4 and 14 mg/kg; 3.3 and 32.5 μmol/kg) was active in the learned helplessness paradigm. However, it had no antidepressant activity in tetrabenazine-induced ptosis or forced swimming test at ≤150 mg/kg (359 μmol/kg). Deramciclane elevated serum prolactin levels and brain dopamine metabolites (DOPAC, HVA) only at 20–40 mg/kg (48–96 μmol/kg). Deramciclane up to 40–100 mg/kg (96–239 μmol/kg) did not modify apomorphine-induced climbing, amphetamine-induced hyperlocomotion, or the conditioned avoidance reaction. Swimming-induced grooming was inhibited only by 50 mg/kg (112 μmol/kg) of deramciclane. Deramciclane reduced the motor activity at doses well above the established anxiolytic doses: ED₅₀ 18 mg/kg; 43 μmol/kg (rats) and 31.5. mg/kg; 75 μmol/kg (mice). Based on these results the anxiolytic-type selectivity of deramciclane appears satisfactory and to have a psychopharmacological profile of its own. Drug Dev. Res. 40:333–348, 1997. © 1997 Wiley-Liss, Inc.     

Synergistic interaction of pregabalin with the synthetic cannabinoid WIN 55,212-2 mesylate in the hot-plate test in mice: an isobolographic analysis

BackgroundThe aim of the study was to determine the type of interaction between pregabalin (a 3^rd-generation antiepileptic drug) and WIN 55,212-2 mesylate (WIN – a highly potent non-selective cannabinoid CB1 and CB2 receptor agonist) administered in combination at a fixed ratio of 1:1, in the acute thermal pain model (hot-plate test) in mice.MethodsLinear regression analysis was used to evaluate the dose-response relationships between logarithms of drug doses and their resultant maximum possible antinociceptive effects in the mouse hot-plate test. From linear equations, doses were calculated that increased the antinociceptive effect by 30% (ED₃₀ values) for pregabalin, WIN, and their combination. The type of interaction between pregabalin and WIN was assessed using the isobolographic analysis.ResultsResults indicated that both compounds produced a definite antinociceptive effect, and the experimentally-derived ED₃₀ values for pregabalin and WIN, when applied alone, were 29.4 mg/kg and 10.5 mg/kg, respectively. With isobolography, the experimentally derived ED_{30 mix} value for the fixed ratio combination of 1:1 was 5.7 mg/kg, and differed significantly from the theoretically calculated ED_{30 add} value of 19.95 mg/kg (p < 0.01), indicating synergistic interaction between pregabalin and WIN in the hot-plate test in mice.ConclusionsIsobolographic analysis demonstrated that the combination of WIN with pregabalin at a fixed ratio of 1:1 exerted synergistic interaction in the mouse model of acute thermal pain. If the results from this study could be adapted to clinical settings, the combination of WIN with pregabalin might be beneficial for pain relief in humans.     

General pharmacology of SDZ WAG 994, a potent selective and orally active adenosine A1 receptor agonist

The pharmacological properties of 6-cyclohexyl-2′-0-methyladenosine (SDZ WAG 994)—a potent, selective, and orally active adenosine A₁ receptor agonist—are described. SDZ WAG 994 is a potent (K_D 23 ± 2 nM, n = 5) and selective (1,090-fold vs. A_2A receptors) displacer of binding to pig striatal A₁ receptors and behaves as a full agonist at the A₁ receptors coupled negatively to adenylate cyclase in rat adipocytes (pEC₅₀ 6.4 ± 0.2, n = 3), those which induce contraction of rat spleen (pEC₅₀ 7.1 ± 0.1, n = 13) and those which suppress the response to autonomic nerve stimulation in guinea-pig ileum (pIC₅₀ 6.6 ± 0.1, n = 4) and rat kidney (pIC₅₀ 6.0 ± 0.1, n = 6). The compound has negligible affinity (pEC₅₀ < 4, n = 5) for the A_2B receptor which mediates relaxation of guinea-pig aorta. In spontaneously hypertensive (SH) rats SDZ WAG 994, 0.05–0.5 mg/kg (0.14–1.4 μmol/kg) po, caused dose-related and sustained (> 5 h) falls in blood pressure (BP) and heart rate (HR) and suppressed plasma renin activity (PRA); the cardiovascular effects could be immediately and fully reversed by an intravenous injection of 8-(p-sulphophenyl)theophylline, 20 mg/kg (56.4 μmol/kg). SDZ WAG 994 given via the food at 0.4 and 1.2 mg/kg/day (1.1 and 3.3 μmol/kg/day) for 7 or 14 days, respectively, induced dose-related hypotension and bradycardia which were well maintained throughout the treatment periods. In the conscious, normotensive dog, SDZ WAG 994, 1 and 3 mg/kg (2.8 and 8.3 μmol/kg) po, induced substantial, sustained falls in BP which were accompanied by tachycardia. In salt depleted squirrel monkeys, SDZ WAG 994, 0.1–0.3 mg/kg (0.28–0.83 m?mol/kg) iv or 0.2–0.6 mg/kg (0.56–1.7 μmol/kg) po caused dose-related and sustained (> 5 h) bradycardia and suppression of PRA but no change in BP. In rhesus monkeys, SDZ WAG 994, 0.1–1.2 mg/kg (0.28–3.3 μmol/kg) po induced sustained bradycardia and suppression of PRA and the plasma free fatty acid and triglyceride concentrations. The data establish SDZ WAG 994 as a potent, selective, and orally active adenosine A₁ receptor agonist with therapeutic potential in certain cardiovascular and/or metabolic disease states. © 1995 Wiley-Liss, Inc.     

Discriminative stimulus effects of the cannabinoid CB1 antagonist SR 141716A in rhesus monkeys pretreated with Δ9-tetrahydrocannabinol

Rationale Drug discrimination can be used to examine tolerance and dependence in agonist-treated animals by establishing an appropriate antagonist as a discriminative stimulus.Objective Establish intravenous SR 141716A as a discriminative stimulus in four rhesus monkeys pretreated with a relatively small dose of Δ⁹-tetrahydrocannabinol (Δ⁹-THC).Methods Rhesus monkeys received i.v. Δ⁹-THC (0.32 mg/kg) and discriminated i.v. SR 141716A (1 mg/kg) from vehicle while responding under a fixed ratio (FR) 5 schedule of stimulus-shock termination.Results The discriminative stimulus effects of SR 141716A were dose-dependent (ED₅₀=0.33 mg/kg) and were mimicked by the CB₁ antagonist AM 251 (ED₅₀=0.98 mg/kg), but not by a benzodiazepine (midazolam) or an N-methyl-D-aspartate antagonist (ketamine). An additional dose (0.32 mg/kg in addition to 0.32 mg/kg administered before the session) of Δ⁹-THC shifted the SR 141716A dose–effect curve 3-fold rightward. Omitting Δ⁹-THC before test sessions resulted in responding on the SR 141716A lever that was attenuated by subsequent administration of Δ⁹-THC (ED₅₀=0.13 mg/kg), CP 55940 (ED₅₀=0.013 mg/kg), and WIN 55212-2 (ED₅₀=0.35 mg/kg); midazolam and ketamine did not attenuate responding on the SR 141716A lever. SR 141716A (1 mg/kg) shifted the Δ⁹-THC and CP 55940 dose–effect curves 3.4-fold rightward; the WIN 55212-2 dose–effect curve was not significantly modified by a dose of 1 mg/kg of SR 141716A.Conclusions SR 141716A can be established as a discriminative stimulus in animals pretreated with Δ⁹-THC, and this assay is selective for cannabinoid activity. Differential antagonism of cannabinoids by SR 141716A might indicate that the mechanism of action of WIN 55212-2 is not identical to other cannabinoids. This study demonstrates that, under the appropriate conditions, drug discrimination has utility for examining cannabinoid dependence and withdrawal.     

A-80426, a potent and selective α2-adrenoceptor antagonist with serotonin uptake-blocking activity and putative antidepressant-like effects: II. Pharmacology profile

A-80426 N-[2-(benzofuran-6-yl)ethyl]-N-[(R)?( + (-5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl methyl]-N-methylamine) is a compound that combines in vitro selective inhibition of serotonin synaptosomal uptake and α₂-adrenoceptor antagonism. In the present studies, A-80426 was evaluated in vivo for its ability to block serotonin uptake and α₂-adrenoceptors. The antidepressant potential of the compound was also assessed. In rats, A-80426 significantly reduced p-chloroamphetamine (PCA)-induced hyperactivity, a measure of the in vivo blockade of serotonin uptake, after acute (ED₅₀ = 13 μmoles/kg, po) and chronic (14 day) (ED₅₀ = 4.1 μmoles/kg, po) dosing. At doses of 6.7 and 22 μmoles/kg, po, A-80426 was effective in this test procedure for at least 12 h following administration. Doses of 6.7 to 224 μmoles/kg, ip, of A-80426, however, failed to block hypothermia and hypoactivity produced by the α₂-adrenoceptor agonist clonidine, and doses of 100 and 300 μmoles/kg, po, were required to blocked clonidine-induced mydriasis. Thus, the in vitro α₂ receptor binding and blocking effects observed with A-80426 did not translate into the in vivo situation. A-80426 was able to reverse the step-down passive avoidance deficit seen in olfactory bulbectomized rats (ED₇₀ = 7.1 μmoles/kg, po), a finding suggesting that the compound has antidepressant potential. The compound was, however, inactive in the tail suspension and forced swim tests of antidepressant activity in mice at doses up to 72 μmoles/kg, ip. In contrast, fluoxetine was active in all three paradigms. Despite its favorable in vitro profile, A-80426 is not an effective α₂ blocker in vivo and is inactive in the behavioral dispair models of depression. It is unlikely that A-80426 would have antidepressant activity equivalent to existing selective serotonin reuptake inhibitors. α₂ blockade as a potential approach to eliciting antidepressant activity is discussed. © 1995 Wiley-Liss, Inc.     

Analgesic profile of the sodium salt of pemedolac

Pemedolac Na, 1-ethyl-1,3,4,9-tetrahydro-4-(phenylmethyl)-pyrano [3,4-b] indole-1-acetic acid sodium salt, exhibited equipotent analgesic effects after oral, iv, and im administration, suggesting that it is well absorbed. In mouse writhing models, the ED₅₀ values ranged from 0.3 mg (0.81 μmol)/kg (vs. acetylcholine) to 4.3 mg (11.6 μmol)/kg (vs. paraphenylbenzoquinone [PBQ]). In the rat Randall-Selitto model, the ED₅₀ o the compound was approximately 0.001 mg (2.7 nmol)/kg, with a flat dose response curve. The peak effects lasted for 7–9 h, 10–18 h, and 5 h following oral, im, and iv injections, respectively. Intracerebroventricular (i.c.v.) injections of pemedolac Na inhibited the PBQ-induced writing in mice with an ED₅₀ of 43.5 μg (0.12 μmol)/mouse, and this effect was not antagonized by naloxone. It was inactive in the hot plate and tail flick tests, demonstrating that pemedolac Na does not act via an opiate mechanism. These results indicate that pemedolac Na is a viable parenteral and oral analgesic, typified by high analgesic potency, a rapid onset and long duration of action, and an extremely wide safety index. © Wiley-Liss, Inc.     

Potentiation of analgesic efficacy but not side effects: co-administration of an α4β2 neuronal nicotinic acetylcholine receptor agonist and its positive allosteric modulator in experimental models of pain in rats

Positive modulation of the neuronal nicotinic acetylcholine receptor (nAChR) α4β2 subtype by selective positive allosteric modulator NS-9283 has shown to potentiate the nAChR agonist ABT-594-induced anti-allodynic activity in preclinical neuropathic pain. To determine whether this benefit can be extended beyond neuropathic pain, the present study examined the analgesic activity and adverse effect profile of co-administered NS-9283 and ABT-594 in a variety of preclinical models in rats. The effect of the combined therapy on drug-induced brain activities was also determined using pharmacological magnetic resonance imaging. In carrageenan-induced thermal hyperalgesia, co-administration of NS-9283 (3.5 μmol/kg, i.p.) induced a 6-fold leftward shift of the dose–response of ABT-594 (ED₅₀ = 26 vs. 160 nmol/kg, i.p.). In the paw skin incision model of post-operative pain, co-administration of NS-9283 similarly induced a 6-fold leftward shift of ABT-594 (ED₅₀ = 26 vs. 153 nmol/kg). In monoiodo-acetate induced knee joint pain, co-administration of NS-9283 enhanced the potency of ABT-594 by 5-fold (ED₅₀ = 1.0 vs. 4.6 nmol/kg). In pharmacological MRI, co-administration of NS-9283 was shown to lead to a leftward shift of ABT-594 dose–response for cortical activation. ABT-594 induced CNS-related adverse effects were not exacerbated in presence of an efficacious dose of NS-9283 (3.5 μmol/kg). Acute challenge of NS-9283 produced no cross sensitization in nicotine-conditioned animals. These results demonstrate that selective positive allosteric modulation at the α4β2 nAChR potentiates nAChR agonist-induced analgesic activity across neuropathic and nociceptive preclinical pain models without potentiating ABT-594-mediated adverse effects, suggesting that selective positive modulation of α4β2 nAChR by PAM may represent a novel analgesic approach.     

Adenosine A1 receptors in rat brain synaptosomes: Transductional mechanisms,effects on glutamate release,and preservation after metabolic inhibition

In order to assess a possible synergistic antinociceptive interactions, the analgesic effects of aspirin per s?s (acetyl salicylic acid or “ASA”), a nonsteroidal anti-inflammatory drug (NSAID), and tramadol s.c. (TRA), an atypical opioid analgesic, administered either separately or in combination were determined in a model of pain-induced functional impairment in the rat, groups of six rats received either vehicle, ASA (175.4, 312.1, 555.1, 987.0, 1, 755.3, or 3, 121.2 μmol/kg) and TRA (21.3, 38.0, 67.5, 120.0, or 213.5 μmol/kg), or a combination of ASA and TRA (24 different combinations). This allowed us to detect the interaction profile of these combinations. The ED₅₀ for either ASA or TRA were 1, 173.5 ± 7.4 μmol/kg and 141.5 ± 6.8 μmol/kg, respectively. The data obtained confirmed an interaction between ASA and TRA and showed antinociception that may be additive or synergistic, depending on the drug ratio administered. Furthermore, eight combinations showed various degrees of potentiation (P < .01), whereas the others (16) exhibited analgesic effects not different from that of ASA alone. The combination of ASA (3, 121.2 μmol/kg) and TRA (120.0 μmol/kg) produced the maximum analgesic effect. However, the combination of ASA (987/ μmol/kg) with TRA (120.0 μmo/kg) produced the highest potentiation effects. This study clearly showed (1) that there is an interaction between ASA and TRA and (2) which combination of these analgesic drugs produced either the maximum analgesic effect or the highest degree of potentiation in the rat. © 1995 Wiley-Liss, Inc.     

Pharmacologic modulation by cetirizine 2 HCl and loratadine of the histamine-induced skin reaction in mice and in humans

In mice, the histamine-induced cutaneous reaction is inhibited by cetirizine with an approached ED₅₀ of 0.04 mg/kg and by loratadine with an approached ED₅₀ of 0.38 mg/kg, both drugsadministered intraperitoneally. At these doses, cetirizine' s onset of activity seems to be more rapid, although both compounds show the same duration for at least 7 hr. Nine healthy volunteers received orally either cetirizine or loratadine (10 mg single dose) or placebo in a double-blind randomized and cross-over study design. Both drugswere significantly more effective than placebo (except loratadine at the 2nd and 24th hr for the wheal with 1 and 10 μg histamine, and at the 2nd hr for the flare with 1 μg histamine). At all times and withboth agonists' concentrations, cetirizine was significantly more potent than loratadine (except at the 24th hr for the wheal with 1 μghistamine). Neither numerous nor marked side effects were found.     

Anticonvulsant Profile of 4-Amino-(2-methyl-4-aminophenyl)benzamide in Mice and Rats

Abstract: An original ameltolide analogue 4-amino-(2-methyl-4-aminophcnyl)benzamide, in which a second amino group has been introduced, was synthesized and evaluated for anticonvulsant activity. After intraperitoneal administration to mice, 4-amino-(2-methyl-4-aminophenyl)benzamide was found active in the maximal electroshock seizure test and against the tonic seizures elicited either by bicuculline or 3-mercaptopropionic acid. 4-amino-(2-methyl-4-arainophenyl)benzamidc (4A-2M4A-PB) gave anti maximal electroshock seizures ED₅₀, of 63 umol/kg (15.4 mg/kg) and a TD₅₀ of 676 μmol/kg (163 mg/kg), yielding a PI of 10.7: the potency is similar to that of the 4-amino-(2-rnethyl-3-aminophenyl)phthalimide (4-A-2M3A-PP), superior to that of 4-amino-(2,6-dimethylphenyl)phlhaiimide (4A-2,6-DMPP), close to that of phenytoin and carbamazepine and inferior to that of ameltolide. 4A-2M4A-PB with an ED₅₀ of 41 [28-60] μmol/kg (9.9 mg/kg) is as active after oral administration to rats as carbamazepine, more active than ameltolide, 4-A-2M3A-PP and phenytoin and slightly less active than the 4A-2,6-DMPP. The introduction of a second amino group on the substituted phenyl ring does not affect drastically the anticonvulsant potency after intraperitoneal administration to mice; moreover, it seems to enhance the activity after oral administration. 4A-2M4A-PB is a good candidate both for further pharmacokinetic studies and for the study of the precise mechanism of action.     

Tricyclic Antidepressant Agents. II. Effect of Oral Administration on the Uptake of 3H-Noradrenaline and 14C-5-Hydroxytryptamine in Slices of the Midbrain-Hypothalamus Region of the Rat

Abstract: The inhibition of the simultaneous uptake of ³H-l-noradrenaline (NA) and ¹⁴C-5-hydroxytryptamine (5-HT) in slices of the midbrain-hypothalamus region of the rat brain after oral administration of desipramine, imipramine, nortriptyline, amitriptyline, chlordesipramine and chlorimipramine was determined. All compounds were more active in inhibiting the NA uptake than the 5-HT uptake. This difference was very marked for desipramine, imipramine, nortriptyline and chlordesipramine. Chlorimipramine was almost as active on the 5-HT uptake (ED₅₀ = 35 mg/kg orally) as on the NA uptake (ED₆₀ = 20 mg/kg orally) and amitriptyline had low activity on both uptake mechanisms (ED₅₀ > 50 mg/kg orally). Desipramine and imipramine were the most active compounds on the NA uptake (ED₅₀ = 8 mg/kg orally for both compounds) and the duration of the action was very long. The ED₅₀ values for nortriptyline and chlordesipramine in inhibiting the NA uptake were about 20 mg/kg orally for both compounds. The inhibition of the 5-HT uptake was less than 50% at 50 mg/kg orally for all compounds except for imipramine (ED₅₀ = 50 mg/kg orally) and for chlorimipramine. The role of the biotransformation for the inhibitory activities of imipramine, chlorimipramine and amitriptyline was investigated in animals pre-treated with SKF 525 A. The inhibitory potency of imipramine was increased by the same factor for both uptake mechanisms probably due to the large increase in the concentration of imipramine in the rat brain, which was demonstrated after the administration of ¹⁴C-imipramine. The inhibitory activity of chlorimipramine was somewhat more increased for the 5-HT uptake than for the NA uptake. The low activity of amitriptyline seems to be mainly due to poor resorption, since pretreatment of the animals with SKF 525 A only slightly increased the potency whereas intraperitoneal injection of amitriptyline had a rather marked effect on the NA uptake (ED₅₀ = 11 mg/kg intraperitoneally).     

L-368,899, a potent orally active oxytocin antagonist for potential use in preterm labor

L-368,899 [1S-(-7,7-dimethyl-2-endo-(2S-amino-4-(methylsulfonyl)butyramido)-bicyclo(2.2.1)-heptan-1-yl)methanesulfonyl)-4-(2-methylphenyl)piperazine] was characterized in vitro and in vivo as a potent and selective, orally bioavailable oxytocin (OT) antagonist. L-368,899 exhibits high affinity for rat (Ki, 3.6 nM) and human (Ki, 13 nM) uterine OT receptors with selectivity versus liver arginine-vasopressin (AVP)-V1 and kidney AVP-V2 receptors in both species. In vitro, L-368,899 is a potent and competitive OT antagonist in the rat isolated uterus (pA2, 8.9) and mouse anococcygeus muscle (pA2, 8.3) and is inactive against a number of different contractile agents in these preparations. L-368,899 also inhibits OT-stimulated phosphatidylinositol turnover in rat uterine slices and exhibits no agonist-like activity in any of the in vitro assays. In vivo, L-368,899 selectively antagonizes the uterine contractile effects of OT in the anesthetized rat given both i.v. and intraduodenally (i.d.) (AD50; 350 μg/kg i.v., 7 mg/kg i.d.) with a moderate duration of action. In near-term pregnant rhesus macaques, L-368,899 is a potent inhibitor of OT-stimulated uterine activity (AD50, 27 μg/kg i.v.) and OT-mediated spontaneous, nocturnal uterine contractions. L-368,899 is orally bioavailable in several species and, combined with adequate aqueous solubility, represents a potential new tocolytic agent for both oral and i.v. use. © 1993 wiley-Liss, Inc.     

Zatosetron,a selective 5-HT3 receptor antagonist: Pharmacological activities of human and animal metabolites

Zatosetron is a potent, orally active 5-HT₃ receptor antagonist with a long duration of activity in laboratory animals and humans. Several metabolites have been detected in plasma and urine of humans and experimental animals receiving zatosetron. The present study was designed to explore the pharmacological activity of the detected metabolites, 3-hydroxyzatosetron, 3-ketozatosetron, and N-desmethylzatosetron, relative to the parent molecule. These three metabolites had relatively high affinity at 5-HT₃ receptors based on in vitro radioligand binding and inhibited serotonin-induced bradycardia in urethane-anesthetized rats after intravenous administration. However, these metabolites had lower affinity and were less potent than zatosetron. Of these metabolites, 3-hydroxyzatosetron (ED₅₀ = 4.0 μg/kg iv) was approximately 5-fold less potent than zatosetron (ED₅₀ = 0.8 μg/kg iv) in vivo and had approximately 10-fold lower affinity at 5-HT₃ receptors in vitro relative to zatosetron. N-desmethylzatosetron and 3-ketozatosetron were approximately 15-fold less potent than zatosetron in vivo as 5-HT₃ receptor antagonists. With regard to duration of activity in vivo, after intravenous administration, 3-hydroxyzatosetron and 3-ketozatosetron blocked 5-HT₃ receptors longer than zatosetron, whereas N-desmethylzatosetron showed a duration of pharmacological activity similar to zatosetron. A fourth metabolite, zatosetron-N-oxide can exist in two isomeric forms, with stereoselective N-oxidation of zatosetron resulting in formation of only one isomer in humans, zatosetron-β-N-oxide. Zatosetron-β-N-oxide had approximately 100-fold lower 5-HT₃ receptor affinity relative to zatosetron and was approximately 150-fold less active as an antagonist at 5-HT₃ receptors in vivo (ED₅₀ = 115 μg/kg iv). Thus, although pharmacological activity was observed with all four metabolites, they were all less active in vivo than zatosetron. Therefore, these metabolites would contribute significantly to the activity of zatosetron only if plasma (and tissue) levels greatly exceeded those of zatosetron. © 1993 Wiley-Liss, Inc.     

Anticonvulsant activity of (+)-5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine (MK-801), a substance with potent anticonvulsant,central sympathomimetic,and apparent anxiolytic properties

MK-801 prevented tonic extensor seizures in the rat induced by bicuclline with the ED₅₀ being 23 μg/kg p.o. Clonazepam, phenobarbital, diazepam, phenytoin, γ-acetylenic GABA, sodium valproate, and trimethadione were all less potent. In mice, MK-801 was likewise the most potent (ED₅₀ = 0.35 mg/kg p.o.) compound in protecting against tonic seizures induced by electroshock. Clonazepam (ED₅₀ = 0.41 mg/kg p.o.) and MK-801 (ED₅₀ = 0.67 mg/kg p.o.) were by far more potent than any of the other anticonvulsants tested versus bicuculline-elicited seizures in mice. Besides being a potent anticonvulsant, MK-801 demonstrated selectivity, since much higher doses were required in mice to block clonic convulsions produced by pentylenetetrazol (ED₅₀ = 11 mg/kg p.o.) and tonic seizures caused by strychnine (ED₅₀ > 15 mg/kg p.o.) than were needed against electroshock or bicuculline. The anticonvulsant (electroshock) effect of MK-801 in mice was unaffected by pretreating the animals with various receptor antagonists (atropine, mecamylamine, chlorpheniramine, tripelennamine, cyproheptadine, cinanserin, methysergide, cimetidine, and propranolol). MK-801 was slightly, but significantly, antagonized by methergoline, naloxone, and theophylline, whereas haloperidol and especially α-adrenoceptor blockers (prazosin, HEAT, phenoxybenzamine) markedly reduced the anticonvulsant effect of MK-801. Haloperidol was selective for MK-801, not affecting the anticonvulsant actions of phenytoin or phenobarbital. Prazosin antagonized phenytoin and phenobarbital, but to a much lesser extent than it antagonized MK-801. MK-801 is an extremely potent and selective anticonvulsant acting at least partly via a catecholaminergic mechanism.     

Anti-inflammatory and diuretic effects of the diterpene ent-dihydrotucumanoic acid

Gymnosperma glutinosum (Spreng) Less (Asteraceae) is a shrub used in traditional medicine for the treatment of inflammatory and renal diseases. The ent-dihydrotucumanoic acid (DTA) is a diterpene obtained from G. glutinosum. This study evaluated the antioxidant, genotoxic, and diuretic properties of DTA, as well as its in vitro and in vivo anti-inflammatory actions. The antioxidant actions of DTA were assessed with the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and 2,2′-diphenyl-1-picrylhydrazyl (DPPH) assays, the genotoxic action was assessed with the comet assay, and the diuretic effects of DTA were assessed using metabolic cages. The anti-inflammatory actions were evaluated using primary murine peritoneal macrophages stimulated with LPS and the λ-carrageenan-induced hind paw edema test. DTA lacked antioxidant (IC₅₀ > 25,000 μg/mL) activity in the ABTS, FRAP, and DPPH assays. DTA at 500–1,000 μg/mL showed moderate genotoxicity. In LPS-stimulated macrophages, DTA showed IC₅₀ values of 74.85 μg/mL (TNF-α) and 58.12 μg/mL (NO), whereas the maximum inhibition of IL-6 (24%) and IL-1β (36%) was recorded at 200 μg/mL. DTA induced in vivo anti-inflammatory effects with ED₅₀ = 124.3 mg/kg. The in vitro anti-inflammatory activity of DTA seems to be associated with the decrease in the release of TNF-α and NO. DTA promoted the excretion of urine (ED₅₀ = 86.9 mg/kg), Na⁺ (ED₅₀ = 66.7 mg/kg), and K⁺ (ED₅₀ = 8.6 mg/kg). The coadministration of DTA with L-NAME decreased the urinary excretion shown by DTA alone. Therefore, the diuretic activity is probably associated with the participation of nitric oxide synthase. In conclusion, DTA exerted anti-inflammatory and diuretic effects, but lacked antioxidant effects.     

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the Golden Syrian hamster

Lethality, pathology, and various clinical chemical parameters were assessed in the hamster following a single ip or po treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). A single dose, 50-day LD₅₀ of greater than 3000 μg TCDD/kg, ip, was obtained for male and female hamsters while the LD₅₀ of orally administered TCDD was found to be 1157 μg/kg. Thus, the hamster appears to be the least sensitive mammalian species to the lethal effect of TCDD that has yet been investigated. TCDD treatment generally reduced the rate of body weight gain, with orally treated hamsters exhibiting the greatest reduction in rate. Thymic atrophy was the most consistent pathologic finding in TCDD treated hamsters. No histopathological changes were seen in the liver, spleen, kidneys, adrenals, or heart. Moderate to severe ileitis and peritonitis were found in many of the hamsters which died following oral treatment with TCDD. This lesion usually affects the distal ileum and consists of a marked hyperplasia of the mucosal epithelium with mild to severe hemorrhaging and necrosis. The intestinal lesion probably contributed in part to the greater lethality of TCDD in orally treated hamsters. A significant increase in serum alkaline phosphatase, bilirubin, protein, iron, cholesterol, and a decrease in serum albumin, chloride, urea nitrogen, and triglycerides were found in hamsters following both ip and po treatment with TCDD.     

Pharmacological activities of TEI-8362, a novel inhibitor of human neutrophil elastase

1. TEI-8362, 4-(N-(3-((3-carboxypropyl)amino)-8-methyl-1-oxo-4-azaisochromen-6- yl)carbamoyl)-4-((phenylmethoxy)carbonylamino)butanoic acid (C26H28N4O9) is a novel inhibitor of human neutrophil elastase (HNE). We evaluated its pharmacological profile in vitro and in vivo. 2. TEI-8362 demonstrated potent inhibition of HNE with a Ki value of 1.38 x 10(-9) M. Its selectivity for HNE among a variety of proteases ranged from 163 fold to 68,000 fold in favour of HNE. 3. The pulmonary haemorrhage that occurred after i.t. instillation of HNE to hamsters was inhibited by either i.t., i.v., or inhalant administration of TEI-8362. 4. Intratracheal administration of lipopolysaccharide induced pulmonary neutrophilia. Twenty-four hours after lipopolysaccharide administration, the additional treatment with formyl-methionyl-leucyl-phenylalanine resulted in a specific neutrophil-dependent acute lung injury. In this model, lung injury was significantly attenuated by i.t., i.v., or inhalant administration of TEI-8362. 5. These pharmacological actions of TEI-8362 suggest that this drug has therapeutic value in the treatment of destructive lung diseases due to neutrophils.