Anti-biofilm activity of A22 ((S-3,4-dichlorobenzyl) isothiourea hydrochloride) against Pseudomonas aeruginosa: Influence on biofilm formation, motility and bioadhesion.

Bacterial biofilms are involved in various medical infections and for this reason it is of great importance understanding adhesion mechanisms of involved microorganisms is essential to develop new strategies of prevention and control. Different approaches have been used for preventing biofilm related infections in health care settings, such as use of surface coatings agents in medical implants. In this context, is necessary to explore new compounds with anti-biofilm activity. Thus, this study evaluated for the first time the action of A22 against biofilms of Pseudomonas aeruginosa PAO1 strain and multi-resistant clinical isolates on biotic and abiotic surfaces. A22 acts as inhibitor of the MreB protein of the bacterial cell wall, causing the rods to change shape to the coccoid form. In this work, A22 at subinhibitory concentrations was able to prevent biofilm formation, and atomic force microscopy images showed that A22 was highly effective in inhibiting adhesion on polyethylene surfaces. Pseudomonas aeruginosa PAO1 exhibited a strong ability to adhere to HeLa cells, and A22 inhibited the aggregation after 4 h of exposure. Swarming and twitching motilities were significantly altered by A22 at subinhibitory concentrations. Thus, by changing the shape of the bacterial cell, many properties can be affected, such as motility, surface adhesion and biofilm formation. This work presents A22 as a promising novel antibacterial or surface coating agent of medical materials.

Homocysteine-induced caspase-3 activation by endoplasmic reticulum stress in endothelial progenitor cells from patients with coronary heart disease and healthy donors.

Previous studies have suggested an association of hyperhomocysteinemia-induced vascular pathology with enhanced apoptotic potential of endothelial progenitor cells in patients with coronary heart disease. Our results indicate that 500 µmol/L homocysteine induced endothelial progenitor cell apoptosis and activation of caspase-3, both of which were abolished by 100 µmol/L and 200 µmol/L salubrinal, an agent that prevents endoplasmic reticulum stress-induced apoptosis. The addition of 500 µmol/L homocysteine caused a release of Ca(2+) from intracellular stores, and enhanced phosphor-eukaryotic initiation factor 2α phosphorylation at Ser51 and the expression of a glucose-regulated protein of 78 kDa and a C/EBP homologous protein independently of extracellular Ca(2+). These effects of homocysteine on endothelial progenitor cells were significantly greater in patients with coronary heart disease than in healthy donors. These findings suggest that homocysteine induces endoplasmic reticulum stress-mediated activation of caspase-3 in endothelial progenitor cells, an event that is enhanced in patients with coronary heart disease. Furthermore, enhanced endoplasmic reticulum stress-mediated activation of caspase-3 in endothelial progenitor cells might be involved in hyperhomocysteinemia-associated vascular pathology.

The impact of different chelating leaving groups on the substitution kinetics of mononuclear Pt(II)(1,2-trans-R,R-diaminocyclohexane)(X-Y) complexes.

A set of three oxaliplatin derivatives containing 1,2-trans-R,R-diaminocyclohexane (dach) as a spectator ligand and different chelating leaving groups X-Y, viz., [Pt(dach)(O,O-cyclobutane-1,1-dicarboxylate)], or Pt(dach)(CBDCA), [Pt(dach)(N,O-glycine)]+, or Pt(dach)(gly), and [Pt(dach)(N,S-methionine)]+, or Pt(dach)(L-Met), where L-Met is L-methionine, were synthesized and the crystal structure of Pt(dach)(gly) was determined by X-ray diffraction. The effect of the leaving group on the reactivity of the resulting Pt(II) complexes was studied for the nucleophiles thiourea, glutathione (GSH) and L-Met under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-vis spectrophotometric techniques. 1H NMR spectroscopy was used to follow the substitution of the leaving group by guanosine 5'-monophosphate (5'-GMP2-) under second-order conditions. The rate constants indicate for all reactions a direct substitution of the X-Y chelate by the selected nucleophiles, thereby showing that the nature of the chelate, viz., O-O (CBDCA2-), N-O (glycine) or S-N (L-Met), respectively, plays an important role in the kinetic and mechanistic behavior of the Pt(II) complex. The k1 values for the reaction with thiourea, L-Met, GSH and 5'-GMP2- were found to be as follows (10(3) k1, 37.5 degrees C, M(-1) s(-1)): Pt(dach)(CBDCA) 61 +/- 2, 21.6 +/- 0.1, 23 +/- 1, 0.352 +/- 0.002; Pt(dach)(gly) 82 +/- 3, 6.2 +/- 0.2, 37 +/- 1, 1.77 +/- 0.01; Pt(dach)(L-Met) (thiourea, GSH) 62 +/- 2, 24 +/- 1. The activation parameters for all reactions studied suggest an associative substitution mechanism.

Intracerebroventricular administration of histamine H3 receptor antagonists decreases seizures in rat models of epilepsia.

The effects of histamine H3 antagonists on amygdaloid kindled and maximal electroshock seizures in rats were studied to determine their potential as new antiepileptic drugs. Under pentobarbital anesthesia, rats were fixed to a stereotaxic apparatus and a stainless steel guide cannula for drug administration was implanted into the lateral ventricle. In amygdaloid kindled seizures, electrodes were implanted into the right amygdala and electroencephalogram was recorded bipolarly; stimulation was applied bipolarly every day by a constant current stimulator and continued until a generalized convulsion was obtained. In the maximal electroshock (MES) seizure test, electroconvulsion was induced by stimulating animals through ear-clip electrodes, and the durations of tonic and clonic seizures were measured. Thioperamide, clobenpropit, iodophenpropit, VUF5514, VUF5515 and VUF4929 caused a dose-dependent inhibition of both seizure stage and afterdischarge (AD) duration of amygdaloid kindled seizures. The duration of tonic seizure induced by MES was also inhibited by H3 antagonists, but the duration of clonic seizures were unchanged. Among the H3 antagonists tested, clobenpropit and iodophenpropit were somewhat more potent than the other drugs on amygdaloid kindled seizures and MES seizures, respectively. These results indicate that some H3 antagonists may be useful as antiepileptic drugs, especially for secondary generalized seizures and/or tonic-clonic seizures in humans.

Involvement of central and peripheral histamine H(3) receptors in the control of the vascular tone and oxygen uptake in the mesenteric circulation of the rat.

Data concerning cardiovascular effects of peripherally and centrally located histamine H(3) receptor stimulation are contradictory, and despite excessive studies their role in the control of the cardiovascular function have not been cleared yet. Effect of histamine H(3) receptors activation have been attributed to modulation of sympathetic system activity but exact role of peripherally and centrally located histamine H(3) receptors stimulation in the modulation of vascular tone of the mesentery and intestinal metabolism remains unexplored. Aim of the present study was to evaluate the role of centrally and peripherally located histamine H(3) receptors in the modulation of vascular tone of the mesentery and metabolic activity of intestinal tissue. In anesthetized rats total mesenteric blood flow (MBF), mucosal intestinal blood flow (LDBF), intestinal oxygen uptake (VO(2)) and arterial pressure (AP) were determined. Intestinal arterial conductance (C) was also calculated. Administration of the selective histamine H(3) receptor agonist imetit (10 micromol/kg i.a) evoked marked changes in hemodynamic and metabolic parameters; MBF, LDBF, C and VO(2) were significantly increased, whereas AP was significantly decreased. Pretreatment with histamine H(3) receptor antagonist clobenpropit (4 micromol/kg i.a.) abolished imetit-induced circulatory and oxygen uptake responses. Clobenpropit (4 micromol/kg i.a.) alone failed to affect the MBF, LDBF, AP, C and VO(2) values. Central administration of imetit (0.1 micromol i.c.v.) markedly increased AP and decreased MBF, LDBF, C and VO(2). Pretreatment with histamine H(3) receptor antagonist clobenpropit (0,4 micromol i.c.v.) diminished circulatory and metabolic responses to centrally injected imetit. Central histamine H(3) receptors blockade by clobenpropit evoked no significant changes in the mesenteric arterial and mucosal microcirculatory blood flow, intestinal metabolism and mean arterial pressure. We conclude that, peripheral histamine H(3) receptors when stimulated decreases vasoconstrictory tone of the mesenteric artery and precapillary structures and evokes increase of intestinal oxygen uptake. This might be in part due to inhibition of sympathetic postganglionic fibers vasopressor activity. Central histamine H(3) receptor stimulation activates vasoconstrictory sympathetic adrenergic system with possible involvement of other, presumably non-histaminergic receptors system. At basal conditions neither central nor peripheral histamine H(3) receptors are involved in the control of mesenteric macro- and microcirculation and intestinal oxygen consumption.

Effects of endogenous histamine on seizure development of pentylenetetrazole-induced kindling in rats.

This study was performed to investigate whether or not endogenous histamine can protect seizure development of pentylenetetrazole (PTZ)-induced kindling in rats. An intracerebroventricular (i.c.v.) injection with clobenpropit (5 and 10 microg), a representative H(3)-antagonist, significantly prolonged the onset of kindling and inhibited the seizure stages in a dose-dependent manner. Its action was significantly reversed by both immepip (2 microg, i.c.v.), an H(3)-agonist, and alpha-fluoromethylhistidine (alpha-FMH, 10 microg, i.c.v.), a selective histidine decarboxylase inhibitor. alpha-FMH (20 microg, i.c.v.) and pyrilamine (1 and 5 mg/kg i.p.), a classical H(1)-antagonist, markedly augmented the severity of seizure development of PTZ-induced kindling. Therefore, these results indicate that brain endogenous histamine plays a certain protective role on seizure development of PTZ-induced kindling in rats, and that its protective roles are mediated by H(1)-receptors.

S-substituted isothioureas are potent inhibitors of nitric oxide biosynthesis in cartilage.

Nitric oxide (NO.) is a multifunctional messenger molecule generated by a family of enzymes, the nitric oxide synthases, and is overproduced in osteoarthritis and rheumatoid arthritis. Chondrocytes are the major native source of NO. in diarthrodial joints. Chondrocytic inducible nitric oxide synthase induced by inflammatory cytokines and bacterial cell wall fragments mediates many of the catabolic events in arthritis. Agents which specifically inhibit chondrocyte inducible NO. synthase, may thus have a role in the management in arthritis. We evaluated a novel class of potential inducible NO. synthase inhibitors, the S-substituted isothioureas, for their ability to inhibit inducible NO. synthase activity in cultured bovine chondrocytes and explants of cartilage from patients with osteoarthritis. Two isothioureas, S-methyl isothiourea and S-(aminoethyl) isothiourea were 2-4 times more potent than NG-monomethyl-L-arginine monoacetate, 5-10 times more potent than aminoguanidine and over 300 times more potent than N omega-nitro-L-arginine and N omega-nitro-L-arginine methyl ester. The rank order of potency of the NO. synthase inhibitors was S-(aminoethyl) isothiourea > S-methyl isothiourea > NG-monomethyl-L-arginine > aminoguanidine > N omega-nitro-L-arginine = N omega-nitro-L-arginine methyl ester. The order of potency was reversed (N omega-nitro-L-arginine methyl ester = N omega-nitro-L-arginine > NG-monomethyl-L-arginine = S-methyl isothiourea > S-(aminoethyl) isothiourea > aminoguanidine) when evaluating the same compounds ability to inhibit constitutive NO. synthase activity in bovine endothelial cells. In comparison to conventional arginine based analogs, the isothioureas represent a more potent and relatively specific class of inhibitors of inducible NO. synthase in cartilage and thus may be beneficial in the management of arthritis.

Keratinocyte growth factor attenuates lung leak induced by alpha-naphthylthiourea in rats.

OBJECTIVE: To investigate the effect of pretreatment with keratinocyte growth factor on acute permeability pulmonary edema. DESIGN: Prospective, randomized, controlled animal study. SETTING: University research laboratory. SUBJECTS: Specific pathogen-free Sprague-Dawley rats. INTERVENTION: Acute permeability pulmonary edema was induced with an injection of alpha-naphthylthiourea, and lung leak was assessed in an isolated perfused lung model over 180 mins. Leak was confirmed with wet/dry lung weight ratios, and the alveolar fluid protein concentration was measured after bronchoalveolar lavage. The effect of pretreatment with keratinocyte growth factor (injected intratracheally 48 hrs before the experiment) on alpha-naphthylthiourea-induced pulmonary edema was assessed (keratinocyte growth factor/alpha-naphthylthiourea group). Control groups (Control and keratinocyte growth factor/Control) were also studied. Histopathology was performed for each of the four groups. MEASUREMENTS AND MAIN RESULTS: The alpha-naphthylthiourea produced an acute permeability pulmonary edema detected by lung leak over the 180-min ex vivo period of monitoring the isolated perfused lung (leak = 8+/-mL; wet/dry weight ratio 14.7+/-2; lavage protein 3.1+/-1 mg/mL). Pretreatment with keratinocyte growth factor significantly attenuated these parameters (leak = 2.3+/-0.4 mL; wet/dry weight ratio 7.1 +/- 0.5; lavage protein 0.28 +/-0.03 mg/mL), which were not significantly different from the control group and the keratinocyte growth factor/control group. Histopathology showed abundant type II pneumocyte hyperplasia in the lungs of animals pretreated with keratinocyte growth factor, and marked pulmonary edema in animals pretreated with alpha-naphthylthiourea. Less edema was apparent in the keratinocyte growth factor/alpha-naphthylthiourea group. All data are expressed as mean +/- SEM. CONCLUSIONS: Pretreatment with keratinocyte growth factor significantly attenuates pulmonary edema induced by alpha-naphthylthiourea. The mechanisms of this protection are likely related to type II pneumocyte hyperplasia, but remain to be specifically elucidated.

Involvement of blood glucose in the dimethylthiourea-induced protection against alloxan-induced diabetes.

Dimethylthiourea (DMTU, 4.0 mmol/kg) injected into mice 30 min prior to alloxan injection markedly protected mice against the diabetogenic actions of 75 mg/kg alloxan. At 30 min after the above dose of DMTU alone (no alloxan), there was a marked rise in blood glucose. Mannoheptulose, an antagonist of glucose action at pancreatic beta-cells, when given 24 min after DMTU and 6 min before alloxan, eliminated the DMTU-induced protection. The protection was also removed in the fasted mice in which DMTU did not cause hyperglycemia. These results indicate that DMTU protected mice from alloxan-induced diabetes by the indirect mechanism of producing hyperglycemia at the time of alloxan injection.

Clobenpropit (VUF-9153), a new histamine H3 receptor antagonist, inhibits electrically induced convulsions in mice.

The effect of clobenpropit (VUF-9153), a new histamine H3 receptor antagonist, on electrically induced convulsions was studied in mice. Clobenpropit significantly and dose dependently decreased the duration of each convulsive phase. Its anticonvulsant effects were prevented by pretreatment with (R)-alpha-methylhistamine and imetit (VUF-8325), histamine H3 receptor agonists. These findings suggest that the effect of clobenpropit on electrically induced convulsions is due to an increase in endogenous histamine release in the brain, which is consistent with biochemical results that clobenpropit increased brain histidine decarboxylase activity dose dependently. The anticonvulsive effect of clobenpropit was antagonized by mepyramine, a histamine H1 receptor antagonist, but not by zolantidine, a histamine H2 receptor antagonist, indicating that histamine released by the anticonvulsant effect of clobenpropit interacts with histamine H1 receptors of postsynaptic neurons. The present findings of the effect of clobenpropit on electrically induced convulsions are fully consistent with those of thioperamide as described previously (Yokoyama et al., 1993, Eur. J. Pharmacol. 234, 129), supporting the hypothesis that the central histaminergic neuron system is involved in the inhibition of seizures.

Protection of rats against the effects of alpha-naphthylthiourea (ANTU) by elevation of non-protein sulphydryl levels.

We have investigated the influence of the elevation of pulmonary glutathione (GSH) levels on the toxicity of the rodenticide alpha-naphthylthiourea (ANTU) to rat lung. Administration of phorone (diisopropylidene acetone; 200 mg/kg i.p.) caused an initial depletion of both pulmonary and hepatic GSH followed after 48 hr by a marked elevation in both tissues, due most probably to a compensatory rebound synthesis. In control rats, ANTU produced a dose-dependent lethality, hydrothorax and loss of ability of lung tissue to accumulate adenosine and spermidine (markers of endothelial and epithelial cell function, respectively). These effects were prevented or markedly ameliorated when ANTU was given 48 hr after pretreatment with phorone. The mechanism of the protection by phorone pretreatment against ANTU-induced pulmonary toxicity is unclear. It may be due, in part, to elevated GSH levels in pulmonary endothelial cells and, in addition, to increased detoxification of ANTU in the liver, resulting in a decreased availability to the lung.

Neutrophil-induced erythrocyte injury: a potential cause of erythrocyte destruction in the anemia associated with inflammatory disease.

Activated neutrophils at effector/target ratios of 1:20 to 1:2,000 induced depletion of red blood cell (RBC)-reduced glutathione, increased membrane-bound hemoglobin and methemoglobin, and promoted immunoglobulin binding to the cell membrane. Superoxide dismutase/catalase ameliorated the decrease in reduced glutathione and the increase in methemoglobin and immunoglobulin binding. This is interpreted as evidence that activated neutrophils can alter the antigenic nature of the RBC membrane through generation of toxic oxygen radicals.

Antisecretory and antiulcer activities of a potent new histamine H2-receptor antagonist with an intermediate duration of action.

The antisecretory activities of 4-(dimethylamino)- N-[2-[3-[3-(1-piperidinyl)methyl]phenoxy]propyl]amino]- 1,2,5-thiadiazol-4-yl]amino]ethyl]-butanamide, S-oxide (AY-29,315) and ranitidine were determined in the rat, dog and monkey. In conscious, chronically cannulated rats, AY-29,315 was 10 and 208 times more potent than ranitidine as an inhibitor of spontaneous gastric acid secretion by the p.o. and i.v. routes, respectively. Tolerance did not develop in the conscious rat with either compound when administered for 8 consecutive days at doses equivalent to 4 times their antisecretory ED50. In lumen-perfused, anesthetized rats, AY-29,315 i.v. was 44 times more potent than ranitidine as an inhibitor of dimaprit-induced acid secretion. In the gastric fistula dog, AY-29,315 was 7.5 times more potent than ranitidine as an inhibitor of dimaprit-induced secretion by the i.v. route but 3 times less potent by the oral route. In the monkey, against dimaprit, AY-29,315 was 3 and 12 times more potent than ranitidine by the oral and i.v. routes, respectively. p.o./i.v. ratios indicate that, relative to ranitidine, the bioavailability of AY-29,315 by the oral route was low, particularly in the dog. In the dog, at 4 times the oral ED50 dose, the antisecretory effect of ranitidine lasted 190 +/- 3 min, while that of AY-29,315 lasted more than 9 h. AY-29,315 was 8 times more potent than ranitidine as an inhibitor of acetylsalicylic acid-induced ulcers in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation of rabbit middle cerebral arteries in vitro by H1 histaminergic agonists is inhibited by indomethacin and tranylcypromine.

The H1-histaminergic agonists 2-pyridylethylamine (2-PEA) and 2-methylhistamine relaxed potassium-constricted, perfused, rabbit middle cerebral arteries at low concentrations (3 x 10(-11) to 3 x 10(-8) M) and constricted them at high concentrations (3 x 10(-7) to 3 x 10(-4) M). The relaxation and the contraction were not antagonized by propranolol (up to 3 x 10(-6) M) given 30 min before, suggesting that beta-adrenergic mechanisms were not involved. When 2-PEA was tested on arteries constricted with uridine triphosphate (UTP), similar results were obtained. In the UTP-constricted arteries, the 2-PEA-induced responses were competitively antagonized by 3 x 10(-9) M mepyramine. Together with previous work (Ea Kim et al., 1986), these results are compatible with the hypothesis that H1-receptors were responsible for both the relaxation and the contraction observed. When either indomethacin (10(-8), 3 x 10(-7), or 10(-5) M), dexamethasone (10(-5) M), or tranylcypromine (10(-5) or 10(-4) M) were tested on the response to 2-PEA or 2-methylhistamine, these inhibitors suppressed the relaxation or reversed it to a contraction. Furthermore, they potentiated the contraction induced by these agonists. These results favour the hypothesis that the H1-mediated relaxation in rabbit cerebral arteries may in part involve the release of prostaglandins, especially prostacyclin. The participation of such a prostanoid in histaminergic relaxation seems exclusively an H1-mediated mechanism, since the relaxation induced by the H2-agonist dimaprit (in the presence of mepyramine) was not antagonized by either indomethacin (3 x 10(-7) M) or tranylcypromine (10(-4) M).

Kinetic analysis of the interaction of mifentidine with gastric H2-receptors in the conscious dog.

The H2-receptor antagonists mifentidine and cimetidine were compared for their ability to antagonize the activation of H2-receptors in the conscious dog. Dose-response curves to dimaprit in stimulating gastric secretion were displaced to the right in a dose-related fashion by both drugs. Schild and Eadie-Hofstee analysis of these data indicated that mifentidine and cimetidine inhibited in vivo activation of H2-receptors in a manner compatible with competitive surmountable antagonism. Mifentidine displayed a 24fold greater potency than cimetidine as H2 antagonist in the conscious dog.

Inhibition of dimaprit- and pentagastrin-induced gastric acid secretion in cats by the new histamine H2 antagonist, CM 57755.

The antisecretory effects of CM 57755, a new histamine-H2 receptor antagonist, have been compared with those of cimetidine on gastric acid secretion induced by intravenous infusions of dimaprit or pentagastrin into conscious cats with chronically implanted gastric fistulae. Intravenous infusion of CM 57755 induced a parallel shift to the right of the dimaprit dose-response curve. The potency of CM 57755 was comparable with that of cimetidine as shown by similar doses causing a 5-fold displacement to the right of the dimaprit dose-response curve (4.9 mumol kg-1 h-1 for CM 57755 and 4.7 mumol kg-1 h-1 for cimetidine). Unlike that with dimaprit, the acid secretion stimulated by increasing doses of pentagastrin was inhibited by CM 57755 with depression of the maximal effect, indicating non-competitive antagonism. In a second series of experiments the time course of the anti-secretory action of intragastrically administered CM 57755 was studied from the gastric acid secretion induced by constant infusion of dimaprit. At equieffective doses, CM 57755 caused more sustained inhibition than cimetidine.

The effect of the new H2-receptor antagonist mifentidine on gastric secretion, gastric emptying and experimental gastric and duodenal ulcers in the rat: comparison with cimetidine and ranitidine.

The new H2-receptor antagonist mifentidine (DA 4577) was tested for its antisecretory and gastric motor effects in comparison with cimetidine and ranitidine. The Shay rat preparation (5 h) was used for studying gastric secretion; the gastric emptying of a liquid meal was chosen for studying gastric motility. All the three compounds inhibited acid secretion in a dose-dependent fashion. Calculated ED50s were 2.3, 12.2 and 92.8 mg X kg-1 for mifentidine, ranitidine and cimetidine, respectively. Therefore, in this animal model, mifentidine was about 40 times more potent than cimetidine and 5 times more potent than ranitidine. As far as gastric emptying is concerned, the effect of equiactive antisecretory doses (i.e. the respective ED50s calculated from the previously established dose-response curves) of all the three antagonists was completely different. Cimetidine delayed emptying rate, whereas ranitidine accelerated it and mifentidine was completely ineffective. However, at higher doses, also this compound affected emptying rate by reducing it dose-dependently. Gastric and duodenal ulcers were induced in the rat by dimaprit (100 mg X kg-1 intravenously) and cysteamine (250 mg X kg-1 subcutaneously), respectively. As far as gastric ulcer is concerned, the ED50s (the effective dose which protected 50% of the animals from lesions) were 0.23, 4.40 and 9.70 mg X kg-1 for mifentidine, ranitidine and cimetidine, respectively. As regards duodenal ulcer, the ED50 was 4.48 for mifentidine and 150.00 mg X kg-1 for ranitidine. In this animal model, the efficacy of cimetidine was very low. Therefore an ED50 could not be determined. In conclusion, results of the present investigation demonstrated that mifentidine is a potent antisecretory compound and an effective anti-ulcer agent in the rat.

Cimetidine inhibition of dimaprit-induced writhing in the rat.

Intraperitoneal, but not intravenous administration of dimaprit (50-125 mg/kg) caused a dose-dependent writhing in the rat. This effect was blocked, again in a dose-dependent fashion, by cimetidine administered orally 1 h prior to dimaprit. Results obtained suggest that dimaprit induces a cimetidine-sensitive pain by acting at peripheral nociceptive terminals within the peritoneum. The specific (H2-receptor related) analgesic effect of cimetidine could explain its effectiveness in relieving epigastric pain of duodenal ulcer patients treated with the drug.

Antagonism of dithiobiuret toxicity in rats.

Daily administration of dithiobiuret (DTB, 1 mg/kg X 6 days, ip) produced delayed onset muscle weakness in rats as indicated by failure in a treadmill test. In nerve-muscle preparations from DTB-intoxicated rats neuromuscular toxicity was manifested as contractile fatigue during tetanic nerve stimulation. As muscle weakness developed, feed intake decreased and the animals lost body weight. Water intake was not altered during this time, but urine output was increased concomitant with the development of muscle weakness and resulted in a state of negative water balance. Daily administration of d-penicillamine (d-PEN) antagonized DTB-induced treadmill failure in a dose-dependent fashion. A daily dose of d-PEN (1 mMol/kg, ip) that completely antagonized treadmill failure also antagonized the contractile fatigue, reduced feed intake, weight loss and negative water balance caused by DTB administration. In rats already intoxicated with DTB, initiating daily d-PEN treatment or discontinuing further DTB administration, caused the animals to recover normal treadmill performance after a latent period of five days. A single dose of d-PEN (1 mMol/kg, iv) was not effective in reversing treadmill failure or contractile fatigue in rats already intoxicated with DTB. Thus, continuous daily administration of d-PEN was necessary for it to be effective. A single dose of d-PEN (1 m Mol/kg, ip) administered one hr after [14C]-DTB (1 mg/kg, ip) did not affect the plasma and tissue concentrations of DTB-derived radioactivity or their corresponding elimination kinetics. Cumulative urinary and fecal excretion of DTB-derived radioactivity were also unaffected by d-PEN administration as were the relative proportions of DTB and two of its metabolites, monothiobiuret and thiuret, in urine. Other agents that produced dose-dependent antagonism of DTB toxicity were diethyldithiocarbamate, disulfiram, cysteamine and 2,2'-dipyridyl. Considering the chemical and biological properties of DTB and its antagonists, a mechanism of antagonism involving an alteration of the thiol-disulfide and/or divalent metal cation status of motor axon terminals is postulated.

Gastric antisecretory properties of SCH 32651.

This report describes the gastric antisecretory properties of SCH 32651 (3-amino-2-methyl-8-phenylmethoxyimidazo[1,2-a] pyrazine HCl . 1/3 H2O). In the pyloric ligated rat, SCH 32651 inhibited gastric acid secretion; the oral ID50 (95% confidence limits) was 23.7 (13.8-39.2) mg/kg. In Heidenhain pouch dogs, SCH 32651 antagonized histamine-stimulated acid secretion with an ID50 of 1.44 (0.55-3.91) mg/kg p.o. SCH 32651 was also active against secretory responses to dimaprit, pentagastrin and feeding in dogs. In all test models SCH 32651 showed similar potency to cimetidine. Chronic administration of SCH 32651 or cimetidine caused slight tolerance and its antisecretory effect was readily reversible on cessation of dosing. The data indicate that SCH 32651 is an orally effective novel antisecretory drug.