Synthesis of Antiprotozoal 2-(4-Alkyloxyphenyl)-Imidazolines and Imidazoles and Their Evaluation on Leishmania mexicana and Trypanosoma cruzi

Twenty 2-(4-alkyloxyphenyl)-imidazolines and 2-(4-alkyloxyphenyl)-imidazoles were synthesized, with the former being synthesized in two steps by using MW and ultrasonication energy, resulting in good to excellent yields. Imidazoles were obtained in moderate yields by oxidizing imidazolines with MnO2 and MW energy. In response to the urgent need to treat neglected tropical diseases, a set of 2-(4-alkyloxyphenyl)- imidazolines and imidazoles was tested in vitro on Leishmania mexicana and Trypanosoma cruzi. The leishmanicidal activity of ten compounds was evaluated, showing an IC50 < 10 µg/mL. Among these compounds, 27-31 were the most active, with IC50 values < 1 µg/mL (similar to the reference drugs). In the evaluation on epimastigotes of T. cruzi, only 30 and 36 reached an IC50 < 1 µg/mL, showing better inhibition than both reference drugs. However, compounds 29, 33, and 35 also demonstrated attractive trypanocidal activities, with IC50 values < 10 µg/mL, similar to the values for benznidazole and nifurtimox.

The imidazoline I2 receptor agonist 2-BFI reduces abuse-related effects of morphine: self-administration and drug discrimination

RATIONALE

Increasing evidence shows that imidazoline I2 receptor agonists enhance opioid-induced analgesia, suggesting that the combination of I2 receptor agonists with opioids could be a favorable strategy for pain control. However, the effect of I2 receptor agonists on the abuse liability of opioids is unknown. This study examined the impact of the I2 receptor agonist 2-BFI on some abuse-related behavioral effects of the opioid morphine in rats.

OBJECTIVES

The von Frey filament test was used to determine the antinociceptive effects of 2-BFI (intravenous, i.v.) in a rat model of complete Freund's adjuvant (CFA)-induced inflammatory pain. IV self-administration was used to assess the reinforcing effects of 2-BFI alone and to assess the effects of non-contingent injections of 2-BFI (i.p.) on morphine self-administration. A two-lever drug discrimination paradigm in which rats were trained to discriminate 3.2 mg/kg morphine (i.p.) from saline was used to examine whether 2-BFI or another I2 receptor agonist 2-(4,5-dihydroimidazol-2-yl)quinoline hydrochloride (BU224) affected the discriminative stimulus effects of morphine.

RESULTS

2-BFI could not maintain reliable self-administration behavior in rats with no pain or CFA-treated inflammatory pain. However, pretreatment with 2-BFI (i.p.) produced dose-dependent decreases in the dose-effect curve of morphine self-administration. Both 2-BFI and BU224 did not substitute for morphine but significantly attenuated the discriminative stimulus effects of morphine.

CONCLUSIONS

These results suggest that I2 receptor agonists do not enhance, but in fact appear to decrease, the abuse liability of opioids, further supporting the potential utility of I2 receptor agonist-opioid combination therapy for pain control.

Insights into the Pharmacokinetics and In Vitro Cell-Based Studies of the Imidazoline I2 Receptor Ligand B06

The impact of neurodegenerative diseases (ND) is becoming unbearable for humankind due to their vast prevalence and the lack of efficacious treatments. In this scenario, we focused on imidazoline I₂ receptors (I₂-IR) that are widely distributed in the brain and are altered in patients with brain disorders. We took the challenge of modulating I₂-IR by developing structurally new molecules, in particular, a family of bicyclic α-iminophosphonates, endowed with high affinity and selectivity to these receptors. Treatment of two murine models, one for age-related cognitive decline and the other for Alzheimer's disease (AD), with representative compound B06 ameliorated their cognitive impairment and improved their behavioural condition. Furthermore, B06 revealed beneficial in vitro ADME-Tox properties. The pharmacokinetics (PK) and metabolic profile are reported to de-risk B06 for progressing in the preclinical development. To further characterize the pharmacological properties of B06, we assessed its neuroprotective properties and beneficial effect in an in vitro model of Parkinson's disease (PD). B06 rescued the human dopaminergic cell line SH-SY5Y from death after treatment with 6-hydroxydopamine (6-OHDA) and showed a crucial anti-inflammatory effect in a cellular model of neuroinflammation. This research reveals B06 as a putative candidate for advancing in the difficult path of drug discovery and supports the modulation of I₂-IR as a fresh approach for the therapy of ND.

Single-Step Sustainable Production of Hydroxy-Functionalized 2-Imidazolines from Carbohydrates

Manufacturing valuable N-containing chemicals from biomass is highly desirable yet challenging. Herein, a novel strategy was developed for efficient production of 2-(1-hydroxyethyl)-imidazoline (HI), a high-value and versatile building block for synthesizing a myriad of bioactive targets, directly from carbohydrates under mild reaction conditions. With this strategy, bio-based HI was produced from fructose in one step with as high as 77 C % isolated yield in the presence of ethylenediamine (EDA) and InCl₃ at 130 °C. The synergistic functions of EDA and InCl₃ were identified for the transformation, wherein EDA promoted the scission of C-C bond of fructose backbone via retro-aldol (R-A) reaction and rapidly trapped in-situ formed reactive carbonyl-containing C₃ intermediate for HI formation to avoid undesired side reaction, and InCl₃ facilitated the formation of this C₃ intermediate and the final 1,2-hydrid shift step.

Studies of binding by 2-imidazolines to human serum albumin and alpha1-acid glycoprotein by high-performance affinity chromatography

2-Imidazoline drugs are used in a variety of applications, such as the treatment of hypertension and opioid withdrawal. It is known these drugs bind to serum proteins and have significant variations within this class of compounds in the overall level of this binding. However, little specific information is available on the interactions of these compounds with the two major transport proteins for many drugs, human serum albumin (HSA) and alpha₁-acid glycoprotein (AGP). This study examined binding by 2-imidazolines to these proteins by using 25 mm × 2.1 mm i.d. high-performance affinity microcolumns that contained HSA or AGP. The drugs that were examined were antazoline, clonidine, dexmedetomidine, lofexidine, moxonidine, phentolamine, and tizanidine, which represented a wide range of structures and pharmaceutical applications. The major metabolite of lofexidine, N-(2-aminoethyl)-2-(2,6-dichlorophenoxy) propenamide (LADP), was also examined. All these 2-imidazolines were found to have weak-to-moderate binding to HSA, with global affinities that ranged from 1.62 × 10² to 1.07 × 10⁴ M^-1 at pH 7.4 and 37 °C. These compounds had stronger binding with AGP, with global affinities constants ranging from 3.80 × 10² to 1.85 × 10⁴ M^-1. No stereoselectivity was observed by HSA for the enantiomers of dexmedetomidine, lofexidine, or LADP. However, AGP did show some stereoselectivity for lofexidine and LADP but not for dexmedetomidine. These results provide a better understanding of interactions of 2-imidazoline with HSA vs AGP in the circulation and of how this binding can change between drugs within this class of compounds.

Synergistic inhibitory effects of free nitrous acid and imidazoline derivative on metal corrosion in a simulated water injection system

To maintain the integrity of the internal surfaces of the pipelines in oil and gas industry, chemicals, including corrosion inhibitors and biocides, are commonly dosed to prevent corrosion. Imidazoline and its derivatives are widely used corrosion inhibitors for the protection of oil pipelines, which have been shown effective in reducing general corrosion. As an effective biocide, free nitrous acid (FNA) is suitable to inhibit microbially influenced corrosion, induced by for example sulfate-reducing bacteria. In this paper, we hypothesize that the continuous addition of imidazoline and intermittent dosing of FNA, when used in combination, would yield effective control of both general and pitting corrosions. As a typical imidazoline derivative, N-b-hydroxyethyl oleyl imidazoline (HEI-17) was applied in conjunction with intermittent dosing of FNA in the experimental system, with the results compared with two control systems, one receiving HEI-17 only, and one receiving no chemical dosing. The corrosion properties were monitored with open circuit potential, electrochemical impedance spectroscopy, linear polarization resistance, 3D optical profiling, and weight-loss measurement. Following a single dose of FNA, the general corrosion rates in the experimental reactor dropped up to 50% of that in the reactor receiving continuous HEI-17 dosing (0.27 ± 0.04 vs. 0.54 ± 0.08 mm/y), but gradually recovered to 93.4% of that in 2.5 months. After the FNA treatment, the pitting corrosion was decreased by 64.6% compared with continuous HEI-17 dosing reactor for a month from measuring the cumulative distribution of the pitting depth. HEI-17 treatment alone showed moderate pitting corrosion inhibition effect (approx. 27%), and the FNA treatment inhibited the formation of deep pits effectively. The combined application of HEI-17 and FNA has shown synergistic effects and high efficiency in mitigating MIC in the simulated water injection system. This treatment strategy has strong potential to be applied in the practical oilfield operations.

Effects of imidazoline and nonimidazoline α-adrenoceptor agonists and antagonists, including xylazine, medetomidine, dexmedetomidine, yohimbine, and atipamezole, on aggregation of feline platelets

OBJECTIVE

To examine the effects of imidazoline and nonimidazoline α-adrenergic agents on aggregation of feline platelets.

SAMPLE

Blood samples from 12 healthy adult cats.

PROCEDURES

In 7 experiments, the effects of 23 imidazoline and nonimidazoline α-adrenoceptor agonists or antagonists on aggregation and antiaggregation of feline platelets were determined via a turbidimetric method. Collagen and ADP were used to initiate aggregation.

RESULTS

Platelet aggregation was not induced by α-adrenoceptor agonists alone. Adrenaline and noradrenaline induced a dose-dependent potentiation of ADP- or collagen-induced aggregation. Oxymetazoline and xylometazoline also induced a small potentiation of ADP-stimulated aggregation, but other α-adrenoceptor agonists did not induce potentiation. The α₂-adrenoceptor antagonists and certain imidazoline α-adrenergic agents including phentolamine, yohimbine, atipamezole, clonidine, medetomidine, and dexmedetomidine inhibited adrenaline-potentiated aggregation induced by ADP or collagen in a dose-dependent manner. The imidazoline compound antazoline inhibited adrenaline-potentiated aggregation in a dose-dependent manner. Conversely, α₁-adrenoceptor antagonists and nonimidazoline α-adrenergic agents including xylazine and prazosin were ineffective or less effective for inhibiting adrenaline-potentiated aggregation. Moxonidine also was ineffective for inhibiting adrenaline-potentiated aggregation induced by collagen. Medetomidine and xylazine did not reverse the inhibitory effect of atipamezole and yohimbine on adrenaline-potentiated aggregation.

CONCLUSIONS AND CLINICAL RELEVANCE

Adrenaline-potentiated aggregation of feline platelets may be mediated by α₂-adrenoceptors, whereas imidazoline agents may inhibit in vitro platelet aggregation via imidazoline receptors. Imidazoline α-adrenergic agents may have clinical use for conditions in which there is platelet reactivity to adrenaline. Xylazine, medetomidine, and dexmedetomidine may be used clinically in cats with minimal concerns for adverse effects on platelet function.

Enantioselective HPLC Analysis to Assist the Chemical Exploration of Chiral Imidazolines

In the present work, we illustrate the ability of high-performance liquid chromatography (HPLC) analysis to assist the synthesis of chiral imidazolines within our medicinal chemistry programs. In particular, a Chiralpak^® IB^® column containing cellulose tris(3,5-dimethylphenylcarbamate) immobilized onto a 5 μm silica gel was used for the enantioselective HPLC analysis of chiral imidazolines synthesized in the frame of hit-to-lead explorations and designed for exploring the effect of diverse amide substitutions. Very profitably, reversed-phase (RP) conditions succeeded in resolving the enantiomers in nine out of the 10 investigated enantiomeric pairs, with α values always higher than 1.10 and R_S values up to 2.31. All compounds were analysed with 50% (v) water while varying the content of the two organic modifiers acetonitrile and methanol. All the employed eluent systems were buffered with 40 mM ammonium acetate while the apparent pH was fixed at 7.5. Based on the experimental results, the prominent role of π-π stacking interactions between the substituted electron-rich phenyl groups outside of the polymeric selector and the complementary aromatic region in defining analyte retention and stereodiscrimination was identified. The importance of compound polarity in explaining the retention behaviour with the employed RP system was readily evident when a quantitative structure-property relationship study was performed on the retention factor values (k) of the 10 compounds, as computed with a 30% (v) methanol containing mobile phase. Indeed, good Pearson correlation coefficients of retention factors (r - log k_1st = −0.93; r - log k_2nd = −0.94) were obtained with a water solubility descriptor (Ali-logS). Interestingly, a n-hexane/chloroform/ethanol (88:10:2, v/v/v)-based non-standard mobile phase allowed the almost base-line enantioseparation (α = 1.06; R_S = 1.26) of the unique compound undiscriminated under RP conditions.

Heterogeneous electro-Fenton as plausible technology for the degradation of imidazolinium-based ionic liquids

Conventional water treatments are generally inadequate for degradation of emerging pollutants such as ionic liquids (ILs). The use of heterogeneous electro-Fenton (HEF) has attracted great interest, due to its ability to efficiently oxidize a wide range of organic pollutants operating in cycles or in continuous mode. In this study, the removal of a complex IL from the imidazolinium family (1,3-Bis(2,4,6-trimethylphenyl)imidazolinium chloride), by means of HEF using iron alginate spheres as catalyst has been investigated, resulting in significant TOC decay after 6 h. The optimization of the key process parameters (current, IL concentration and catalyst dosage) has been performed using a Box-Behnken experimental design and achieving 76.98% of TOC abatement in 2 h of treatment. Current proved to be a crucial parameter and high catalyst dosage is required to achieve the maximum removal. In addition, an insight about the availability of iron into the reactor and the evolution of several intermediates has been carried out by employing differential pulse voltammetry on screen-printed carbon electrodes. The evolution of the different voltammetric peaks confirmed the influence of iron release, and the generation of several iron complexes has permitted the comprehension of the degradation pathway, which has been validated by chromatographic techniques.

mRNA imaging in the chloroplast of Chlamydomonas reinhardtii using the light-up aptamer Spinach

Light-up aptamers are practical tools to image RNA localization in vivo. A now classical light-up aptamer system is the combination of the 3,5-difluoro-4-hydroxybenzylidene (DFHBI) fluorogen and the RNA aptamer Spinach, which has been successfully used in bacterial and mammalian cells. However, light-up aptamers have not been used in algae. Here, we show that a simple vector, carrying Spinach, transcriptionally fused to the aphA-6 gene, can be effectively used to generate a functional light-up aptamer in the chloroplast of Chlamydomonas reinhardtii. After incubation with DFHBI, lines expressing the aphA-6/Spinach mRNA were observed with laser confocal microscopy to evaluate the functionality of the light-up aptamer in the chloroplast of C. reinhardtii. Clear and strong fluorescence was localized to the chloroplast, in the form of discrete spots. There was no background fluorescence in the strain lacking Spinach. Light-up aptamers could be further engineered to image RNA or to develop genetically encoded biosensors in algae.

Leaching of three imidazolinone herbicides during sprinkler irrigation

Some imidazolinone herbicides have been shown to be mobile in soil, raising concern about their possible movement to ground water. Three imidazolinone herbicides (imazamethabenz-methyl, 497 g ha(-1); imazethapyr, 14.7 g ha(-1); and imazamox, 14.7 g ha(-1)) commonly used in crop production on the Canadian prairies were applied to a tile-drained field to assess their susceptibility to leach when subjected to sprinkler irrigation using a center pivot. Tile-drain flow began when the water table rose above tile-drain depth, and peak flow rates corresponded to the greatest depths of ground water above the tile drains. Interception of irrigation water by the tile drains in each quadrant of the field varied from ∼11 to 20% of the water applied. Under a worst-case scenario in which irrigation began the day after herbicide application and irrigation water was applied at 25 mm d(-1) for 12 d, there was evidence of preferential flow of all three herbicides and hydrolysis of imazamethabenz-methyl to imazamethabenz in the initial samples of tile-drain effluent. In subsequent samples, concentrations (analysis by LC-MS-MS) of the summation of imazamethabenz-methyl (25-24,000 ng L(-1)) plus its hydrolysis product imazamethabenz (63-26,500 ng L(-1)) greatly exceeded those of imazethapyr (<13-1260 ng L) and imazamox (19-599 ng L(-1)), thus reflecting relative application rates. In contrast, estimates of total transport of each herbicide from the root zone, which varied in each quadrant and ranged from 0.06 to 2.3% for imazamethabenz-methyl plus imazamethabenz, 0.71 to 3.1% for imazethapyr, and 0.61 to 2.8% for imazamox, did not reflect application rates. In shallow ground water (piezometer samples), there was inconsistent and infrequent detection all four compounds. With the frequency and amount of rainfall typically encountered in the prairie region of Canada, contamination of shallow ground water with detectable concentrations of the three imidazolinone herbicides would be unlikely.

Structure, dynamics and optical properties of fluorescent proteins: perspectives for marker development

GFP-like proteins, originally cloned from marine animals, are genetically encoded fluorescence markers that have become indispensable tools for the life sciences. The search for GFP-like proteins with novel and improved properties is still ongoing, however, driven by the persistent need for advanced and specialized fluorescence labels for cellular imaging. Overall, the structures of these proteins are similar, but considerable variations have been found in the covalent structures and stereochemistry of the fluorophore, which govern essential optical properties such as the absorption/emission wavelengths. Moreover, as the fluorophore-enclosing cavity forms its solvation shell, it can also have a significant effect on the absorption/emission wavelengths and the brightness of the fluorophore. Most exciting are recent developments of photoactivatable fluorescence markers which change their color and/or intensity upon irradiation with light of specific wavelengths. A detailed understanding of the structure and dynamics of GFP-like proteins greatly aids in the rational engineering of advanced fluorescence marker proteins. Herein, we review our present knowledge of the structural diversity of GFP-like proteins and discuss how structure and dynamics govern their optical properties, with an emphasis on red fluorescent proteins.

Voltage- and NADPH-dependence of electron currents generated by the phagocytic NADPH oxidase

The phagocytic NADPH oxidase generates superoxide by transferring electrons from cytosolic NADPH to extracellular O2. The activity of the oxidase at the plasma membrane can be measured as electron current (I(e)), and the voltage dependence of I(e) was recently reported to exhibit a strong rectification in human eosinophils, with the currents being nearly voltage independent at negative potentials. To investigate the underlying mechanism, we performed voltage-clamp experiments on inside-out patches from human eosinophils activated with PMA. Electron current was evoked by bath application of different concentrations of NADPH, whereas slow voltage ramps (0.8 mV/ms), ranging from -120 to 200 mV, were applied to obtain 'steady-state' current-voltage relationships (I-V). The amplitude of I(e) recorded at -40 mV was minimal at 8 microM NADPH and saturated above 1 mM, with half-maximal activity (K(m)) observed at approx. 110 microM NADPH. Comparison of I-V values obtained at different NADPH concentrations revealed that the voltage-dependence of I(e) is strongly influenced by the substrate concentration. Above 0.1 mM NADPH, I(e) was markedly voltage-dependent and steeply decreased with depolarization within the physiological membrane potential range (-60 to 60 mV), the I-V curve strongly rectifying only below -100 mV. At lower NADPH concentrations the I-V curve was progressively shifted to more positive potentials and I(e) became voltage-independent also within the physiological range. Consequently, the K(m) of the oxidase decreased by approx. 40% (from 100 to 60 microM) when the membrane potential increased from -60 to 60 mV. We concluded that the oxidase activity depends on both membrane potential and [NADPH], and that the shape of the I(e)-V curve is influenced by the concentration of NADPH in the submillimolar range. The surprising voltage-independence of I(e) reported in whole-cell perforated patch recordings was most likely due to substrate limitation and is not an intrinsic property of the oxidase.

Superoxide does not mediate the acute vasoconstrictor effects of angiotensin II: a study in human and porcine arteries

OBJECTIVE

To investigate whether superoxide mediates angiotensin (Ang) II-induced vasoconstriction.

METHODS

Human coronary arteries (HCAs), porcine femoral arteries (PFA) and porcine coronary arteries (PCAs) were mounted in organ baths and concentration-response curves to Ang II, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and the NAD(P)H oxidase substrate NADH were constructed in the absence and presence of superoxide inhibiting and activating drugs. Extracellular superoxide was measured using cytochrome c reduction.

RESULTS

Ang II constricted both HCAs and PFAs. In HCAs, the NAD(P)H inhibitors diphenyleneiodonium (DPI) and apocynin, and the xanthine oxidase (XO) inhibitor allopurinol, but not the superoxide dismutase (SOD) mimetic tempol or the SOD inhibitor diethyldithiocarbamate (DETCA), reduced this constriction. Catalase potentiated Ang II in HCAs, indicating a vasodilator role for H2O2. DPI, tempol and SOD did not affect Ang II in PFAs. DPI, apocynin and allopurinol relaxed preconstricted HCAs. Although the relaxant effects of the NO donor SNAP in PCAs was reduced by DETCA, indicating that superoxide-induced constrictions depend on NO inactivation, the apocynin-induced relaxations were NO independent. Moreover, NADH relaxed all vessels, and this effect was blocked by KCl but not DPI or NO removal. Xanthine plus XO also relaxed HCAs and PCAs. Incubation of human or porcine arteries with Ang II or NADH did not result in detectable increases of extracellular superoxide within 1 h.

CONCLUSIONS

Acute vasoconstriction by Ang II is not mediated via superoxide generated through NAD(P)H oxidase and/or XO activation. Such activation, if occurring, rather results in the generation of the vasodilator H2O2.

Role of reactive oxygen species in LPS-induced production of prostaglandin E2 in microglia

We determined the roles of reactive oxygen species (ROS) in the expression of cyclooxygenase-2 (COX-2) and the production of prostaglandin E2 (PGE2) in lipopolysaccharide (LPS)-activated microglia. LPS treatment increased intracellular ROS in rat microglia dose-dependently. Pre-treatment with superoxide dismutase (SOD)/catalase, or SOD/catalase mimetics that can scavenge intracellular ROS, significantly attenuated LPS-induced release in PGE2. Diphenylene iodonium (DPI), a non-specific NADPH oxidase inhibitor, decreased LPS-induced PGE2 production. In addition, microglia from NADPH oxidase-deficient mice produced less PGE2 than those from wild-type mice following LPS treatment. Furthermore, LPS-stimulated expression of COX-2 (determined by RT-PCR analysis of COX-2 mRNA and western blot for its protein) was significantly reduced by pre-treatment with SOD/catalase or SOD/catalase mimetics. SOD/catalase mimetics were more potent than SOD/catalase in reducing COX-2 expression and PGE2 production. As a comparison, scavenging ROS had no effect on LPS-induced nitric oxide production in microglia. These results suggest that ROS play a regulatory role in the expression of COX-2 and the subsequent production of PGE2 during the activation process of microglia. Thus, inhibiting NADPH oxidase activity and subsequent ROS generation in microglia can reduce COX-2 expression and PGE2 production. These findings suggest a potential therapeutic intervention strategy for the treatment of inflammation-mediated neurodegenerative diseases.

Caspase regulation of genotoxin-induced neural precursor cell death

Neural precursor cells (NPCs) critically regulate brain morphogenesis and recent studies have revealed an unexpectedly high frequency of NPC chromosomal abnormalities and apoptosis in the developing brain. We have shown previously that the apoptotic response of NPCs to genotoxic agents is dependent on p53 and caspase-9, but not Bax or caspase-3 expression. In this study, we found that NPCs deficient in Apaf-1, or both the pro-apoptotic multidomain Bcl-2 family members Bax and Bak, were resistant to cytosine arabinoside and gamma-irradiation-induced apoptosis. Inhibitors of gene transcription, protein translation, and caspase activity also blocked genotoxin-induced NPC apoptosis. Although caspase-3 and caspase-6 were both cleaved in response to DNA damage, neither of these effector caspases was critical for apoptosis. Genotoxin-induced NPC death was accompanied by the generation of reactive oxygen species and could be inhibited by several known antioxidants. Conversely, DNA damage-induced reactive oxygen species generation was inhibited significantly by gene disruption of p53, Apaf-1, or caspase-9, and combined deficiency of Bax and Bak, but not by caspase-3 or caspase-6 deficiency. These studies suggest that caspase-9 activation is both necessary and sufficient for genotoxin-induced neural precursor cell reactive oxygen species generation and death.

Differential effects of vitamin E and three hydrophilic antioxidants on the actinomycin D-induced and colcemid-accelerated apoptosis in human leukemia CMK-7 cell line

The actinomycin D (AD)-induced apoptosis in human leukemia CMK-7 cell line is greatly accelerated by microtubule disruption with colcemid (CL). We studied the effect of antioxidants on this apoptosis in order to learn how the universal signal mediators, reactive oxygen species (ROS), are involved. Caspase-3 activation and DNA fragmentation were both suppressed by vitamin E (VE), t-butylhydroxyanisole, and luteolin. The ROS formation in the AD treatment was evidenced by flow cytometry, and further supported by suppression of caspase-3 activation by superoxide radical-forming enzyme inhibitors (TTFA, rotenone, and DPI). The inhibition of apoptosis by VE was completed during the initial 1-h treatment with AD, but it did not appear when VE was added with CL to washed cells after AD treatment. Luteolin, an iron chelator PDTC, and a water-soluble VE analogue, trolox, inhibited the apoptosis when added with CL after the AD treatment. Western blot analysis showed that the proteolytic cleavage of procaspase-9 and procaspase-3 were both inhibited when VE was added with AD or when luteolin was added with CL, and that the cytochrome c liberation was suppressed by both antioxidants. This result implies that the ROS are initially formed in lipophilic environments (e.g. mitochondrial membrane) and then they diffuse into an aqueous environment (i.e. cytoplasm) where they promote the apoptotic process in combination with the cytoskeletal disruption. Thus, the different antioxidants are effective to scavenge ROS for preventing the apoptosis in its different phases.

Reactive oxygen species production in association with suberization: evidence for an NADPH-dependent oxidase

In response to wounding, potato tubers generate reactive oxygen species (ROS) in association with suberization. Immediately following wounding, an initial burst of ROS occurs, reaching a maximum within 30 to 60 min. In addition to this initial oxidative burst, at least three other massive bursts occur at 42, 63 and 100 h post-wounding. These latter bursts are associated with wound healing and are probably involved in the oxidative cross-linking of suberin poly(phenolics). The source of ROS is likely to be a plasma membrane NADPH-dependent oxidase immunorelated to the human phagocyte plasma membrane oxidase. The initial oxidative burst does not appear to be dependent on new protein synthesis, but the subsequent bursts are associated with an increase in oxidase protein components. Oxidase activity is enhanced in vitro by hydroxycinnamic acids and conjugates associated with the wound healing response in potato.

Evidence that hydroxyl radicals mediate auxin-induced extension growth

Reactive oxygen intermediates, i.e. the superoxide radical (O*-)(2), hydrogen peroxide (H2O2) and the hydroxyl radical (*OH), are generally regarded as harmful products of oxygenic metabolism causing cell damage in plants, animals and microorganisms. However, oxygen radical chemistry may also play a useful role in polymer breakdown leading to wall loosening during extension growth of plant cells controlled by the phytohormone auxin. Backbone cleavage of cell wall polysaccharides can be accomplished in vitro by (*OH) produced from H2O2 in a Fenton reaction or in a reaction catalyzed by peroxidase supplied with O2 and NADH. Here, we show that coleoptile growth of maize seedlings is accompanied by the release of reactive oxygen intermediates in the cell wall. Auxin promotes release of (O*-)(2) and subsequent generation of (*OH)when inducing elongation growth. Experimental generation of (*OH) in the wall causes an increase in wall extensibility in vitro and replaces auxin in inducing growth. Auxin-induced growth can be inhibited by scavengers of (O*-)(2), H2O2 or (*OH), or inhibitors interfering with the formation of these molecules in the cell wall. These results provide the experimental background for a novel hypothesis on the mechanism of plant cell growth in which (*OH), produced from (O*-)(2) and H2O2 by cell wall peroxidase, acts as a wall-loosening agent.

The binding of oxidized low density lipoprotein (ox-LDL) to ox-LDL receptor-1 reduces the intracellular concentration of nitric oxide in endothelial cells through an increased production of superoxide

Oxidized low density lipoprotein (ox-LDL) has been suggested to affect endothelium-dependent vascular tone through a decreased biological activity of endothelium-derived nitric oxide (NO). Oxidative inactivation of NO is regarded as an important cause of its decreased biological activity, and in this context superoxide (O(2)) is known to inactivate NO in a chemical reaction during which peroxynitrite is formed. In this study we examined the effect of ox-LDL on the intracellular NO concentration in bovine aortic endothelial cells and whether this effect is influenced by ox-LDL binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1) through the formation of reactive oxygen species and in particular of O(2). ox-LDL induced a significant dose-dependent decrease in intracellular NO concentration both in basal and stimulated conditions after less than 1 min of incubation with bovine aortic endothelial cells (p < 0.01). In the same experimental conditions ox-LDL also induced O(2) generation (p < 0.001). In the presence of radical scavengers and anti-LOX-1 monoclonal antibody, O(2) formation induced by ox-LDL was reduced (p < 0.001) with a contemporary rise in intracellular NO concentration (p < 0.001). ox-LDL did not significantly modify the ability of endothelial nitric oxide synthase to metabolize l-arginine to l-citrulline. The results of this study show that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the inactivation of NO through an increased cellular production of O(2).

Rhinovirus-induced oxidative stress and interleukin-8 elaboration involves p47-phox but is independent of attachment to intercellular adhesion molecule-1 and viral replication

Virus-induced elaboration of proinflammatory cytokines is mediated by virus-induced oxidative stress. The purpose of these studies was to determine the source of the virus-induced oxidative stress. Inhibition of viral replication with antibody to intercellular adhesion molecule-1 had no effect on virus-induced oxidative stress or interleukin-8 (IL-8) response (597+/-88 vs. 668+/-78 pg/mL in control cells). Treatment of cells with diphenylene iodonium inhibited virus-induced oxidative stress and IL-8 elaboration, but allopurinol, ibuprofen, and rotenone had no effect. Studies in cell lines produced from a patient with gp91-phox deficiency revealed normal responses. In contrast, the oxidative response was decreased and the IL-8 concentration was 227+/-36 pg/mL in cells from a patient with p47-phox deficiency, compared with 664+/-48 pg/mL in control cells. These studies suggest that the stimulation of reactive oxygen species by viral challenge occurs at the cell surface even in the absence of viral replication and involves a flavoprotein that may act in concert with p47-phox.

Selective modulation of membrane currents by hypoxia in intact airway chemoreceptors from neonatal rabbit

1. We previously described voltage-dependent ionic currents and hypoxia chemosensitivity in cultured pulmonary neuroepithelial body (NEB) cells isolated from fetal rabbit. Here we use fresh neonatal rabbit lung slices (200-400 micrometer thick) to characterize the electrophysiological properties of 'intact' NEBs with patch-clamp, whole-cell recording. 2. Under voltage clamp, outward currents were partially inhibited by TEA (20 mM), 4-amino pyridine (4-AP; 2 mM) and cadmium (Cd2+; 100 micrometer), suggesting the presence of both Ca2+-dependent (IK(Ca)) and Ca2+-independent (IK(V)) components. 3. Inward currents, carried by voltage-dependent Ca2+ channels and also, in occasional cells (approximately 11%), by TTX-sensitive Na+ channels, were also detected in intact NEB cells. 4. Hypoxia (PO2 = 15-20 mmHg) reduced the outward K+ current by approximately 34% during voltage steps from -60 to +30 mV, while inward Ca2+ or Na+ currents were not affected by hypoxia. Hypoxia suppressed roughly equally both IK(Ca) and IK(V) components of outward current, and no further inhibition of K+ currents was seen with either TEA and 4-AP + hypoxia. 5. Diphenylene iodonium (DPI; 1 microM) suppressed outward K+ current by approximately 42%, and DPI + hypoxia had no additional effect on the K+ current. 6. Direct application of H2O2 augmented outward K+ current; for a voltage step from -60 mV to +30 mV, 0.25 mM H2O2 increased K+ current by approximately 37%. 7. These results indicate that intact neonatal NEB cells express hypoxic chemosensitivity and introduce the rabbit lung slice preparation as an new model for investigating the role of airway O2 chemoreceptors.

Probing cellular protein targets of H2O2 with fluorescein-conjugated iodoacetamide and antibodies to fluorescein

Recent studies suggest that H2O2, at subtoxic concentrations generated in response to the activation of a variety of cell surface receptors, functions as an intracellular messenger. However, the intracellular targets of H2O2 action have not been identified. A procedure to detect proteins with reactive cysteine residues susceptible to oxidation by intracellularly generated H2O2 is now described. This approach is based on the labeling of proteinaceous cysteine with 5-iodoacetamidofluorescein at pH 5.5 and immunoblot analysis of the labeled proteins with antibodies specific to fluorescein. With this procedure, many proteins in human A431 cells were shown to contain reactive cysteines and to be readily oxidized by H2O2 generated in response to cellular stimulation with epidermal growth factor. One of these H2O2-sensitive proteins was identified as protein tyrosine phosphatase 1B.

Role of the retrorubral nucleus in striatally elicited orofacial dyskinesia in cats: effects of muscimol and bicuculline

Orofacial dyskinesia (OFD) is a disorder characterized by involuntary movements of the oral and facial muscles. OFD attacks can be elicited acutely in cats by local injections of dopaminergic agents into the anterodorsal part (r-CRM) of the caudate nucleus. Because the dopaminergic A8 cell group, being embedded in the retrorubral nucleus (RRN), gives rise to fibres which terminate in the r-CRM, two questions arose: (1) whether the A8 cell group forms part of the circuitry that directs and/or modulates OFD, and (2) whether GABA-ergic compounds in the RRN play a role in OFD, and if so, whether a pharmacological GABA-ergic intervention of the activity in the RRN modulates or mediates OFD. For this purpose, the activity of the RRN was manipulated with local injections of the GABA(A) agonist muscimol and antagonist bicuculline. These local injections into the RRN were subsequently combined with manipulations of dopamine transmission in the r-CRM with local injections of the selective DAi receptor agonist (3,4-dihydroxyphenylimino)-2-imidazoline. The present study shows that local injections of GABA-ergic compounds into the RRN do not elicit OFD attacks in cats, but can modulate oral behaviour elicited from the r-CRM. The latter effect is dose dependent and GABA-ergic specific.

Activation of N-methyl-D-aspartate receptors in the feline retrorubral nucleus elicits orofacial dyskinesia

Stimulation of dopamine receptors within a circumscribed subregion of the feline caudate nucleus, that is the anterodorsal part of this nucleus, with dopamine or the dopamine receptor agonist (3,4-dihydroxyphenylimino)-2-imidazoline (DPI) elicits orofacial dyskinesia. Orofacial dyskinesia is a syndrome of tic-like contractions of the facial muscles which ends with a tongue protrusion. Afferent fibres of the anterodorsal part of the caudate nucleus are known to emanate from the retrorubral nucleus, including the dopaminergic A8 cell group. The present study was undertaken to investigate whether excitation of A8 cells can mediate and/or modulate orofacial dyskinesia. For this purpose, the activity of the retrorubral nucleus was manipulated with local injections of N-methyl-D-aspartate (NMDA). These local injections into the retrorubral nucleus were subsequently combined with manipulations of the dopamine transmission in the anterodorsal part of the caudate nucleus with local injections of DPI. The present study shows that injections of NMDA into the retrorubral nucleus elicits orofacial dyskinesia. This effect is dose-dependent, NMDA-specific, and inhibited by intra-caudate injections of DPI.

Identification of gestationally regulated genes in rat myometrium by use of messenger ribonucleic acid differential display

OBJECTIVE

We hypothesized that the proteins contributing to myometrial changes during gestation could be identified indirectly by analyzing the changing pattern of messenger ribonucleic acid expression in the myometrium during pregnancy.

STUDY DESIGN

Ribonucleic acid was extracted from myometrium of timed pregnant Sprague-Dawley rats on days 12, 16, 20, 21, and 22 of pregnancy and on day 1 post partum. The technique of messenger ribonucleic acid differential display, a simple and sensitive polymerase chain reaction-based method for rapidly identifying messenger ribonucleic acids whose levels increase or decrease, was performed with the nine different anchoring primers (oligodeoxythymidine11 VN: V = G, A, or C; N = G, A, or C) in combination with 24 different 10-base oligonucleotides of random sequence. The polymerase chain reaction products were separated by electrophoresis on a 5% polyacrylamide sequencing gel, and those whose levels changed were then cloned, sequenced, and compared with those in the GenBank database to determine whether they corresponded to a known sequence in the database or were novel. Semiquantitative reverse transcriptase-polymerase chain reaction was used to confirm differential expression of selected products.

RESULTS

Messenger ribonucleic acid differential display revealed > 500 polymerase chain reaction products that were differentially expressed during gestation, 179 of which were cloned and sequenced. Of these, 157 were from messenger ribonucleic acids whose levels increased during gestation, and 22 were from transcripts that decreased. Eighty-seven (49%) were related to sequences in the GenBank database, of which 62 (35%) were from messenger ribonucleic acids encoding known proteins and 25 (14%) corresponded to known expressed sequence tags. The technique of semiquantitative reverse transcriptase-polymerase chain reaction confirmed the increased expression of messenger ribonucleic acids encoding beta-tropomyosin, type II phosphatidyl inositol-4-phosphate 5-kinase, and a novel myometrial messenger ribonucleic acid named RPU0901AC.

CONCLUSION

Messenger ribonucleic acid differential display is a simple and sensitive method for rapidly identifying myometrial messenger ribonucleic acids that are differentially regulated during pregnancy. The identification of these differentially expressed messenger ribonucleic acids may lead to a better understanding of the molecular basis of normal and abnormal parturition.

d-Sulpiride inhibits oral behaviour elicited from the nucleus accumbens of freely moving rats

The present study analyzed the effect of intra-accumbens administration of the stereoisomers of sulpiride upon (3,4-dihydroxyphenylimino)-2-imidazoline (DPI)-induced changes in oral behaviours and electromyographic patterns of jaw muscles. In line with earlier findings, DPI (5 micrograms) administered into the nucleus accumbens increased chewing and tremor. l-Sulpiride (2-50 ng) had no effect on DPI-induced oro-facial behaviours. d-Sulpiride (10-50 ng) significantly antagonized the DPI-induced increase in chewing and had a biphasic effect on tremor with potentiation (10 ng) followed by attenuation (50 ng). When administered alone, l- or d-sulpiride did not affect oro-facial behaviours. The electromyographic signals, which were analyzed according to a previously described method, were described with the help of three classes: A (the seconds marked by frequency 3 Hz), B (the seconds marked by the frequencies 4-6 Hz); C (the seconds marked by the frequencies 7-15 Hz). DPI enhanced Class B and C of the masseter muscle but did not significantly affect any frequency class of the digastric muscle. l-Sulpiride (2-50 ng) had no effect on DPI-induced (5 micrograms) changes in electromyographic signals. d-Sulpiride (50 ng) antagonized the effects of DPI on Class B of the masseter muscle. Furthermore, d-sulpiride had a biphasic effect on Class C with potentiation (10 ng) followed by attenuation (50 ng). When administered alone, l- or d-sulpiride did not affect the frequency classes of the jaw muscles. It is concluded that d-sulpiride inhibits DPI-induced changes in oral behaviour and electromyographic patterns. It is suggested that d-sulpiride may be effective in the pharmacotherapy of oro-facial dyskinesias in man.

Vascular pharmacology of methylene blue in vitro and in vivo: a comparison with NG-nitro-L-arginine and diphenyleneiodonium

1. The vascular effects of the soluble guanylyl cyclase inhibitor, methylene blue as well as the nitric oxide (NO) synthase inhibitors, NG-nitro-L-arginine (L-NOARG) and diphenyleneiodonium (DPI) were studied in rat isolated aortic rings and conscious, unrestrained rats. 2. Acetylcholine (ACh) and sodium nitroprusside (SNP) caused concentration-dependent relaxation of preconstricted aortic rings. Both methylene blue (1 x 10(-5) M) and L-NOARG (3 x 10(-5) M) abolished ACh-induced relaxation; however, methylene blue but not L-NOARG shifted the concentration-response curve of SNP to the right. 3. In conscious rats, i.v. infusion of methylene blue (1.1 x 10(-5) mol kg-1 min-1), at a concentration which reduced the aortic tissue level of cyclic GMP by 50%, did not significantly alter mean arterial pressure (MAP) and heart rate (HR). In contrast, i.v. bolus injection of L-NOARG (1.5 x 10(-4) mol kg-1) markedly increased MAP and decreased HR. 4. Both ACh and SNP dose-dependently decreased MAP in conscious rats. Methylene blue did not alter the magnitude or duration of ACh- or SNP-induced depressor responses. L-NOARG, on the other hand, significantly though incompletely, reduced the magnitude and duration of the depressor response to ACh but not SNP. The depressor response to ACh or SNP was not altered by pretreatment with indomethacin (1.4 x 10(-5) mol kg-1) or capsaicin (3.3 x 10(-4) mol kg-1). 5. NG-nitro-L-arginine methyl ester (L-NAME) also caused dose-dependent increases in MAP in conscious rats. Both methylene blue and DPI (1 x 10-5 mol kg-1) selectively shifted the dose-pressor response curve of L-NAME to the right.6. These results suggest that: (1) the inhibition of endogenous NO biosynthesis does not necessarily lead to pressor response in vivo, (2) L-NOARG may not produce pressor response solely via the inhibition of endogenous endothelial NO biosynthesis, and (3) the depressor responses to ACh and SNP may not involve the release of NO or prostanoids or afferent nerve transmitters.

NG-nitro-L-arginine contracts vascular smooth muscle by an endothelium-independent mechanism

We characterized the contractile effect of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) in endothelium-denuded rat aortic rings. Incubation with L-NNA (4 x 10(-6)-6.4 x 10(-5) M) for 5 h dose-dependently contracted endothelium-denuded aortic rings. In contrast, incubation with NG-nitro-D-arginine (D-NNA 6 x 10(-6)-4 x 10(-4) M), diphenyleneiodonium (DPI, NO synthase inhibitor, 3.2 x 10(-6) M) or dexamethasone (10(-7) M, inhibitor of expression of inducible NO synthase) did not contract the denuded rings. The L-NNA-induced contraction was not significantly altered by the presence of the endothelium or by pretreatment with L-arginine (L-Arg 2 x 10(-3) M) or lipopolysaccharide (100 ng/ml). These results suggest that L-NNA causes slow contraction of endothelium-denuded vascular smooth muscle (VSM) by a mechanism independent of the inhibition of constitutive or inducible NO biosynthesis.

Relative roles of elastase and reactive oxygen species in the degradation of human glomerular basement membrane by intact human neutrophils

Glomerular basement membrane (GBM) damage and proteinuria occurring during the early phase of acute glomerulonephritis are often neutrophil (PMN) dependent. The present study sought to identify the potential roles of PMN derived elastase and reactive oxygen species (ROS) in the pathogenesis of glomerular basement damage in an homologous in vitro model of anti-GBM nephritis using intact PMN. Human PMN (5 x 10(6)), incubated with human GBM (0.5 mg) pretreated with human anti-GBM IgG, degraded 10.3 +/- 1.1% of the GBM type IV collagen in six hours (8 micrograms/hr), and underwent a two-hour respiratory burst. The same number of sonically disrupted PMN solubulized 22.4 +/- 5.1% of GBM under the same incubation conditions. The inclusion of the elastase inhibitors alpha 1 proteinase inhibitor (alpha 1Pi), and a smaller highly-specific synthetic compound (L658,758), reduced degradation by PMN homogenates by 84.8% and 85.7%, respectively, whereas they were only able to inhibit intact PMN mediated degradation by a maximum of 49.2% and 50.9%, respectively. The inclusion of EDTA (10 mM), an inhibitor of metalloproteinases, reduced GBM degradation by APMA activated and disrupted PMN by only 7.5%. Incubation of PMN with diphenylene iodonium (DPI) abolished PMN reactive oxygen species generation by > 95% but preserved elastase release. This compound did not directly affect GBM degradation. It did, however, abolish the inhibitory effect of ROS on alpha 1Pi activity and thus indirectly reduced GBM damage by up to 20%.

Evidence for a role of the shell of the nucleus accumbens in oral behavior of freely moving rats

Behavioral effects of intra-accumbens administration of the dopamine DAi receptor agonist (3,4-dihydroxyphenylimino)-2-imidazoline (DPI) were studied in freely moving rats. Three distinct areas were examined: core, shell and "shore," namely, the border region of the core and shell. DPI (5 micrograms) administered into the shell, but not areas ventral to the shell, increased chewing, tongue protrusion, sniffing, and grooming; it also induced abnormal oral behavior, namely, large-amplitude chewing. A similar dose of DPI administered into the core did not affect any (peri-)oral behavior, except sniffing. Because of methodological constraints the receptor specificity of the DPI effects was studied in rats with cannulas directed at the shore. DPI (5.0-10.0 micrograms) administered into the shore increased oral behavior dose dependently; however, the dose-effect curve varied per distinct type of oral behavior. The dopamine DAi receptor antagonist ergometrine attenuated the effect of DPI on tremor, chewing, and sniffing frequencies. Taken together, the data show that the effects of DPI were DAi receptor specific. It is concluded that stimulation of dopamine DAi receptors in the shell modulates and induces (peri-)oral behaviors in freely moving rats.

Interleukin 1 activates soluble guanylate cyclase in human vascular smooth muscle cells through a novel nitric oxide-independent pathway

Recent demonstration of cytokine-inducible production of nitric oxide (NO) in vascular smooth muscle cells (VSMC) from rat aorta has implicated VSMC-derived NO as a key mediator of hypotension in septic shock. Our studies to determine whether an inducible NO pathway exists in human VSMC have revealed a novel cytokine-inducible, NO-independent pathway of guanylate cyclase activation in VSMC from human saphenous vein (HSVSMC). Interleukin 1 (IL-1), tumor necrosis factor (TNF), interferon gamma (IFN-gamma) and Escherichia coli lipopolysaccharide (LPS) increased cGMP at 24 h, whereas IL-2 and IL-6 were ineffective. The effect of IL-1 on cyclic guanosine 3',5'-monophosphate (cGMP) was delayed, occurring after 6 h of exposure, and was maximal after 10 h. Methylene blue and LY83583 reversed the IL-1-induced increase in cGMP, suggesting that it was mediated by activation of soluble guanylate cyclase. However, IL-1-induced cGMP in HSVSMC was not inhibited by extracellular hemoglobin. Also, the effect of IL-1 on cGMP was not reversed by nitro- or methyl-substituted L-arginine analogs, aminoguanidine, or diphenyleneiodonium, all of which inhibit IL-1-induced NO synthase in rat aortic VSMC (RAVSMC). IL-1-induced cGMP in HSVSMC was also independent of tetrahydrobiopterin and extracellular L-arginine, as it was not affected by 2,4-diamino-6-hydroxyprytimidine, an inhibitor of tetrahydrobiopterin biosynthesis, and was similar in L-arginine-free and L-arginine-containing media. Analysis of NO synthase mRNA with the use of polymerase chain reaction indicates that levels of mRNA for inducible NO synthase are several orders of magnitude lower in IL-1-treated human HSVSMC than in IL-1-treated RAVSMC. IL-1-induced cGMP was also NO independent in human umbilical artery VSMC, and NO dependent in rat vena cava VSMC. Together these results indicate that IL-1 activates a novel NO-independent pathway of soluble guanylate cyclase activation in human VSMC.

Subregions of the caudate nucleus and their in- and output channels in oro-facial dyskinesia: a behavioural and retrograde tracing study in the cat

Previous studies have shown that the feline caudate nucleus contains DPI-sensitive (caput nuclei caudati, anterodorsal part; r-CRM) and DPI-insensitive (caput nuclei caudati, rostromedial part; CRM) regions. Stimulation of dopamine receptors within the r-CRM by dopamine or DPI are known to elicit oro-facial dyskinesia (OFD), i.e. a syndrome of tic-like contractions of the facial muscles in combination with tongue protrusions. OFD is also elicited from the sub-commissural part of the globus pallidus (scGP), a first order output station of the r-CRM, but not from the CRM. On the basis of these data it has been hypothesized that (1) OFD is a specific feature of the r-CRM, but not the CRM; (2) effects elicited from the r-CRM are funneled via the scGP, and that (3) r-CRM and CRM are differentially innervated. Cats were bilaterally equipped with cannulas directed at the CRM or r-CRM and scGP. Following recovery from the operation the cats received bilateral injections of DPI into CRM (5 micrograms/5 microliter) or r-CRM (5 and 10 micrograms/5 microliter), the latter in combination with muscimol (50 and 100 ng/1 microliter) into the scGP or its solvent. Subsequently, behaviour was analyzed. OFD, quantified in number of tongue protrusions, was only elicited from the r-CRM, but not from the CRM confirming previously reported data in this respect. Furthermore the effect varied according to the dose used. The OFD elicited from the r-CRM was found to be blocked at the level of the scGP by local injections of muscimol, a GABA agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the nucleus accumbens in social memory in rats

Recognition of a juvenile conspecific by an adult male rat is known to be reflected by reduced anogenital investigation (A.G.I.) of this young individual by the adult, when the two animals are reexposed to each other after some short delay. As the delay is increased, the reduction in A.G.I. is reduced. This measure of social memory can be modulated by several drugs, among others cholinomimetic agents. In this study, the effects of direct manipulation of the nucleus accumbens were studied. Local administration of (3,4-dihydroxyphenylimino)-2-imidazoline (DPI: 0.1-1.5 micrograms) decreased investigatory behaviour at the second exposure after a long interexposure-interval, while ergometrine (0.1 micrograms) counteracted this reduction by DPI. These findings suggest a role for the nucleus accumbens in social recognition, in particular for the so-called DAi receptors which are stimulated and inhibited by DPI and ergometrine respectively.

On the mechanism of drug-induced blockade of Na+ currents: interaction of antiarrhythmic compounds with DPI-modified single cardiac Na+ channels

In patch-clamped membranes from neonatal rat cardiocytes, elementary Na+ currents were recorded at 19 degrees C for study of the inhibitory influence of several antiarrhythmic drugs including lidocaine, diprafenone, propafenone, and prajmalium on DPI-modified cardiac Na+ channels. Diprafenone (20 mumol/l) and lidocaine (300 mumol/l) induced a voltage- and time-dependent block of reconstructed macroscopic sodium current (INa). The drugs depressed the sustained, noninactivating INa component (which reflects the number and open probability of DPI-modified Na+ channels) effectively, in a voltage- and time-dependent fashion. Once opened, DPI-modified Na+ channels are highly drug-sensitive. Antiarrhythmic drugs (propafenone, diprafenone, and, to a lesser extent, lidocaine) provoke a flicker block, that is, the long-lasting openings are chopped into a large number of short and grouped openings. This indicates rapid transitions between a drug-associated, blocked state and a drug-free, conducting state. The latter has a unitary conductance of 12 pS, very similar to the control value in the absence of antiarrhythmic drugs. The decrease in open time of drug-treated DPI-modified Na+ channels is concentration-dependent. Hill coefficients for propafenone of about 1.0 and for prajmalium of about 0.7 were calculated. A blocking rate constant of 6.1 x 10(7) mol-1sec-1 for propafenone, but of 1.5 x 10(7) mol-1sec-1 for prajmalium was obtained at -30 mV. The unblocking rate constant for propafenone was, also at -30 mV, about twice as large as the unblocking rate constant for prajmalium. The open channel block kinetics are essentially voltage-dependent. The affinity of the channel-associated drug receptor increases on membrane depolarization. The blocking rate constant was inversely related to the number of Na+ ions moving through the open channel. It is concluded that the manifestation of this voltage- and Na+-dependent flicker block is intimately related to removal of fast Na+ inactivation.

The pharmacological characterization of 3,4-dihydroxyphenylimino-2-imidazolidine (DPI) as a potent mixed alpha 1/alpha 2-adrenoceptor agonist rather than as a dopamine receptor agonist

In the past decade many studies have been carried out on the pharmacological actions of the imidazoline derivative DPI (3,4-dihydroxyphenylimino-2-imidazolidine) because it has been proposed as a selective agonist at a postulated subtype of dopamine (DA) receptor. According to the first publication on this concept of multiple DA receptors, authored by Cools & van Rossum (1976), mammalian DA receptors can be divided into excitation-mediating (DAe) and inhibition-mediating (DAi) receptors. DAe receptors appeared to coincide with ‘classical’ DA receptors i.e. those that can be selectively stimulated with apomorphine and inhibited with haloperidol, whereas the newly postulated DAi receptors could be selectively stimulated with DPI and inhibited with ergometrine (Cools & van Rossum 1976, 1980). Though interesting from a conceptual point of view, the idea of the existence of DAi receptors in the mammalian brain was rather speculative, and Cools and coworkers consequently put much effort into attempting to provide it with an experimental basis. They found that in some test models DPI and ergometrine had indeed opposing effects, and they explained these results as being in strong support of the presence of DAi receptors and thus of the validity of the DAe/DAi concept (Cools et al 1976; Cools 1977). In spite of the latter conclusion, however, these authors have repeatedly revised their original concept, i.e. by the additional postulations of the ‘alpha-like norepinephrine receptor’ (Cools & van Rossum 1980) and of the ‘DAi/e receptor’ (Cools 1981).

Interaction between the inhibitory action of acetylcholine and the alpha-adrenoceptor autoinhibitory feedback system on release of [3H]-noradrenaline from rat atria and rabbit ear artery

Stimulation-induced increases in the efflux of radioactivity (S-I efflux) were measured in the bathing medium following labelling of the noradrenergic transmitter pools of rat atria and rabbit artery preparations with [3H]-noradrenaline. In atria stimulated with trains of 16 or 60 pulses at 2 Hz, phentolamine enhanced, whereas acetylcholine inhibited S-I efflux. With trains of 16 pulses phentolamine had a smaller enhancing effect than with trains of 60 pulses, whereas the inhibitory effect of acetylcholine was more pronounced with 16 pulses of stimulation. The inhibitory effect of acetylcholine was markedly enhanced by phentolamine when stimulation was with 60 pulses. With 16 pulses of stimulation the effect of acetylcholine was unaltered by phentolamine and abolished by the alpha 2-adrenoceptor agonist 3,4-dihydroxyphenylimino-2-imidazolidine (DPI). Phentolamine had no effect on the negative inotropic effect of acetylcholine on driven left atrial preparations. In arterial preparations stimulated with trains of 30 pulses at 1 Hz, both acetylcholine and clonidine inhibited S-I efflux, whereas yohimbine and idazoxan enhanced S-I efflux. Combining acetylcholine with clonidine did not alter the inhibitory effect of clonidine but the combination of acetylcholine with yohimbine or idazoxan abolished the marked enhancing effects of yohimbine or idazoxan on S-I efflux. These findings indicate that there may be a reciprocal interaction between prejunctional alpha-adrenoceptors and prejunctional muscarinic cholinoceptors.

Differentiation of basal ganglia dopaminergic involvement in behavior after hippocampectomy

Large bilateral aspiration lesions of the hippocampus in rats lead to a variety of changes in spontaneous behavior measured in an open field/hole board, relative to sham and neocortically lesioned controls. These changes include increased locomotion, and decreased grooming frequency and rearing bout duration. When animals were injected with the dopamine (DA) agonist 3,4-dihydroxyphenylamino-2-imidazoline (DPI: 0.5, 1.0 and 5.0 microgram) into the nucleus accumbens one week after surgery, the behavior of hippocampally lesioned rats was restored to levels not different from control lesioned rats. Haloperidol injections (0.05, 0.1 and 0.5 microgram) into the caudate nucleus were not able to do this. Further, DPI injected into the caudate month after surgery was also able to attenuate some of the effects of hippocampal damage. On the other hand, haloperidol injections into the nucleus accumbens did not influence behavior. The results are interpreted in terms of hippocampal lesion-induced alteration of a balance in basal ganglia DA systems, indicated by modified response to pharmacological intervention and which mediate the behavioral effects of the lesion.

The purported dopamine agonist DPI inhibits [3H]noradrenaline release from rat cortical slices but not [3H]dopamine and [14C]acetylcholine release from rat striatal slices in-vitro

The effects of the purported dopamine (DA) receptor agonist (3,4-dihydroxyphenylimino)-2-imidazolidine (DPI) upon the in-vitro K+-induced release of [3H]DA and [14C]acetylcholine from rat neostriatal slices, and of [3H]noradrenaline from rat neocortical slices have been investigated and compared with those of the DA receptor agonist TL-99 and the alpha-adrenoceptor agonist clonidine, respectively. The rapid decomposition of the catechol compounds DPI and TL-99 in the Krebs-Ringer bicarbonate superfusion medium was shown to be inhibited by both the chelating agent EDTA and the reducing agent ascorbic acid. The results suggest that in-vitro DPI is unable to stimulate striatal DA receptors, whereas it is effective in stimulating cortical alpha 2-adrenoceptors (EC50 = 61 nM). It is concluded that DPI should be considered as a mixed alpha 1/alpha 2-adrenoceptor agonist and that the designation of DPI as a DA receptor agonist should be abandoned.

Differential effect of calcium entry blockers on alpha 1-adrenoceptor-mediated vasoconstriction in vivo

The effects of the calcium entry blockers nifedipine, (-)-verapamil and the dihydropyridine derivative PY 108-068 were evaluated on the increase in diastolic pressure of pithed normotensive rats caused by the selective alpha 1-adrenoceptor agonists cirazoline, (-)-phenylephrine, (+/-)-erythro-methoxamine, (-)-amidephrine and St 587 [(2-chloro-5-trifluoromethylphenylimino)-2-imidazolidine] as well as by the mixed alpha 1/alpha 2-adrenoceptor agonists clonidine and DPI [(3,4-dihydroxyphenylimino)-2-imidazolidine]. The calcium entry inhibitors (up to 3 mg/kg) caused 3- to 5-fold, parallel rightward shifts of the log dose-pressor effect curves to cirazoline, (-)-phenylephrine, (+/-)-erythro-methoxamine and (-)-amidephrine accompanied by only a slight depression of the maximal pressor response. In contrast, the calcium entry inhibitors produced a dose-dependent profound depression of both maximum and slope of the log dose-pressor response curves to St 587 and clonidine. For DPI about 10- and 100-fold parallel displacements to the right without reduction of the maximum were found following treatment with 1 and 3 mg/kg of nifedipine, respectively. Infusion of vasopressin to counteract the vasodilatory action produced by the calcium entry inhibitors did not significantly change the pattern of interference observed under the conditions of decreased baseline diastolic pressure. The results indicate that alpha 1-adrenoceptor-mediated vasoconstriction in the pithed normotensive rat, which is characterized by its sensitivity to blockade by prazosin and its relative insensitivity to antagonism by yohimbine or rauwolscine, can be subdivided into two distinct processes which are differentially influenced by blockade of calcium entry.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-disubstituted phenyliminoimidazolidines as potential prodrugs of the purported dopamine agonist 3,4-dihydroxyphenylimino-2-imidazolidine (DPI)

A series of ether derivatives of the purported dopamine agonist 3,4-dihydroxyphenylimino-2-imidazolidine (DPI) has been prepared as potential prodrugs of the parent compound due to its relatively poor penetration into the brain. Their effects on both dopamine and noradrenaline utilization in the rat brain have been investigated using the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine. Apart from the parent compound, DPI, the diphenylmethane ether analogue showed some dopaminergic activity.

Effects of DPI (2-(3,4-dihydroxyphenylimino)-imidazolidine) on prejunctional alpha-adrenoceptors and prejunctional dopamine receptors in the rabbit ear artery

The effects of DPI on transmitter noradrenaline release were examined in rabbit isolated ear arteries previously incubated in [ 3H ]noradrenaline. DPI (0.1 mumol/l) reduced transmitter release with periarterial electrical stimulation at 1 Hz (1 ms pulses, supramaximal voltage for 30 s), which is consistent with an agonistic effect of DPI on prejunctional alpha-adrenoceptors. At stimulation frequencies of 2 or 5 Hz DPI alone did not affect release, however in the presence of phentolamine (3 mumol/l, which increased release per se) DPI again significantly reduced release; this effect was blocked by metoclopramide (1 mumol/l) indicating an agonistic effect of DPI on prejunctional dopamine receptors.

The purported dopamine agonist (3,4-dihydroxyphenylimino)-2-imidazolidine (DPI) acts as a nonselective alpha-adrenoceptor agonist in inducing hypertension, hypomotility and hypothermia in the rat

Following peripheral administration the purported dopamine (DA) agonist (3,4-dihydroxyphenylimino)-2-imidazolidine (DPI) was shown to increase the diastolic blood pressure of pithed rats and to decrease rat motility and rectal temperature. Dose-effect relationships were established and half-maximal effective doses for the hypertensive and hypothermic response to DPI were calculated to be 4.4 nmol/kg i.v. and 2.0 mumol/kg i.p., respectively. Pretreatment with various antagonists revealed that both alpha 1- and alpha 2-adrenergic mechanisms were responsible for the DPI-induced hypertension, hypomotility and hypothermia, indicating that DPI acts as a non-selective alpha-adrenoceptor agonist. Qualitatively the DPI-induced effects were found to correlate well with those reported for its structural analogue clonidine, thus suggesting a similar mechanism of action for these agents. DA receptor antagonists appeared to lack inhibitory potency towards any of DPI-elicited responses. The results do not therefore support the designation of DPI as a DA receptor agonist.

Time course of certain behavioral changes after hippocampal damage and their alteration by dopaminergic intervention into nucleus accumbens

Independent groups of rats with hippocampal, neocortical, or sham lesions were observed 7, 14, or 28 days after surgery in an open field-hole board apparatus and in a smaller circular apparatus. In the circular apparatus, animals were observed after unilateral injection of the dopamine agonist, 3,4-dihydroxyphenylamino-2-imidazoline (DPI) or saline into nucleus accumbens. Behavioral changes in locomotion, exploration and grooming measured in the open field were consistent with those found previously after hippocampal damage, with each behavioral anomaly demonstrating a specific pattern of change after surgery. In general, the injection of DPI into nucleus accumbens produced greater behavioral change in animals with hippocampal damage than in animals with either neocortical or sham lesions. The drug-induced changes in the hippocampally lesioned rats made their behavior more like that of control animals. These results suggest that destruction of the hippocampus may induce alterations in dopaminergic mechanisms in nucleus accumbens which can be modified by appropriate pharmacologic intervention.

Evidence that the purported dopaminergic agonist (3,4-dihydroxyphenylimino)-2-imidazolidine (DPI) may reduce rat striatal dopamine turnover by an alpha 2-adrenergic mechanism

The potent alpha-adrenergic agonist DPI, which has also been claimed to be a selective dopaminergic agonist, was shown to reduce rat striatal dopamine (DA) synthesis, DA utilization and DA metabolism following intraperitoneal administration (25 mumol/kg). An analytical procedure for the determination of DPI was developed and its application showed that DPI did not penetrate into the brain in substantial amounts. The possibility of a direct stimulatory action upon striatal presynaptic DA receptors was excluded by the demonstration that DPI lacked effectiveness both in the gamma-butyrolactone model and following intrastriatal administration. The selective alpha-adrenergic agonists phenylephrine (alpha 1) and tramazoline (alpha 2) decreased and increased DA metabolism, respectively, the yohimbine-induced increase being antagonized by DPI. The carbon-bridge analogue (3,4-dihydroxybenzyl)-2-imidazoline (DHBI) had about the same activity as DPI, whereas the potential DPI metabolite (4-hydroxy-3-methoxyphenylimino)-2-imidazolidine (HMPI) was without effect upon striatal DA metabolism. The results are discussed in relation to the remarkable resemblance with the literature data concerning clonidine. It is concluded that the DPI-elicited attenuation of striatal DA turnover is, in all likelihood, the result of a stimulation of alpha 2-adrenoceptors possibly located within the central nervous system. The results cast some doubt on the designation of DPI as a selective DA-inhibitory receptor agonist.

Agonistic actions of DPI (2-(3,4-dihydroxyphenylimino)-imidazolidine) on alpha-adrenoceptors and dopamine receptors

Some of the pharmacological actions of 2-(3,4-dihydroxyphenylimino)-imidazolidine (DPI) were studied in vivo and vitro. DPI (1 nM-100 micro M) had a similar affinity but a lower intrinsic activity on alpha-adrenoceptors in rabbit aortic strips to noradrenaline (1 nM-10 micro M). DPI did not affect the uptake of [3H]noradrenaline in guinea-pig isolated atria. The effects of DPI on dopamine receptors were examined in the dog coronary and renal vasculature and in the rat isolated, perfused kidney. In the dog coronary vasculature DPI (0.005-10 micrograms, i.a.), like dopamine (5-50 micrograms, i.a.), caused an increase in coronary blood flow which was antagonized by the dopamine receptor antagonist, ergometrine. In the renal vasculature of both the rat and the dog, dopamine (5-50 micrograms, i.a.) caused vasodilatation but there was no evidence of an effect of DPI on dopamine receptors. It appears that DPI is a selective agonist for dopamine receptors in the coronary vasculature.