Usnea Acid as Multidrug Resistance (MDR) Reversing Agent against Human Chronic Myelogenous Leukemia K562/ADR Cells via an ROS Dependent Apoptosis.

PURPOSE: Multidrug resistance (MDR) is a major obstacle in chemotherapy of leukemia treatments. In this paper, we investigated Usnea Acid (UA) as MDR reversal agent on hematologic K562/ADR cells via ROS dependent apoptosis. METHODS: CCK8 assay was used to measure cell viability rate of K562/ADR. Intracellular reactive oxygen species (ROS) generation, cell cycle distribution, cell apoptosis were measured with flow cytometry, respectively. Proteins related to apoptosis were measured by Western blot. Intracellular Adriamycin accumulation was observed by confocal microscopy and measured by flow cytometry. RESULTS: In vitro study showed intracellular Adriamycin accumulation was remarkably increased by UA. Cell viability treated with Adr (4 µM) was decreased from 89.8% ± 4.7 to 32% ± 8.9 by combined with UA (4 µM). Adr-induced apoptosis and G1/G0 phase cell cycle arrest were remarkably increased by UA, as well as, intracellular ROS level. However, MDR reversing activity of UA was inhibited by N-acetyl cysteine (NAC), a ROS scavenger. CONCLUSION: These data provide compelling evidence that UA is a promising agent against MDR in leukemia cell line and suggest a promising therapeutic approach for leukemia.

Molecular dynamics-guided discovery of an ago-allosteric modulator for GPR40/FFAR1.

The long-chain fatty acid receptor FFAR1/GPR40 binds agonists in both an interhelical site between the extracellular segments of transmembrane helix (TM)-III and TM-IV and a lipid-exposed groove between the intracellular segments of these helices. Molecular dynamics simulations of FFAR1 with agonist removed demonstrated a major rearrangement of the polar and charged anchor point residues for the carboxylic acid moiety of the agonist in the interhelical site, which was associated with closure of a neighboring, solvent-exposed pocket between the extracellular poles of TM-I, TM-II, and TM-VII. A synthetic compound designed to bind in this pocket, and thereby prevent its closure, was identified through structure-based virtual screening and shown to function both as an agonist and as an allosteric modulator of receptor activation. This discovery of an allosteric agonist for a previously unexploited, dynamic pocket in FFAR1 demonstrates both the power of including molecular dynamics in the drug discovery process and that this specific, clinically proven, but difficult, antidiabetes target can be addressed by chemotypes different from existing ligands.

Modulation of prepulse inhibition and stereotypies in rodents: no evidence for antipsychotic-like properties of histamine H3-receptor inverse agonists.

RATIONALE: H(3)-receptor inverse agonists raise a great interest as innovative therapeutics in several central disorders. Whereas their procognitive properties are well established, their antipsychotic-like properties are still debated. OBJECTIVES: We further explored the effect of maximal doses (3-10 mg/kg) of ciproxifan, BF2.649, and ABT-239, three selective H(3)-receptor inverse agonists, on deficits of prepulse inhibition (PPI) induced by apomorphine, MK-801, and phencyclidine (PCP). Their effect was also investigated on stereotypies induced by apomorphine and methamphetamine. RESULTS: Ciproxifan, BF2.649, and ABT-239 did not reverse the PPI impairment produced by apomorphine (0.5 mg/kg, subcutaneous) in rats. Ciproxifan and BF2.649 did not reverse the impairment induced in mice by MK-801 (0.3 mg/kg). Ciproxifan and BF2.649 also failed to reverse the disruption induced in mice by PCP (5-10 mg/kg). Low to moderate doses of haloperidol (0.1-0.4 mg/kg, intraperitoneal), alone or co-administered with BF2.649, did not reverse MK-801-induced PPI disruption. A high dose (1 mg/kg) of haloperidol partially reversed the MK-801-induced deficit and BF2.649 tended to increase this effect, although nonsignificantly. Whereas stereotypies induced in mice by apomorphine and methamphetamine were totally suppressed by haloperidol, the decrease induced by ciproxifan was partial against apomorphine and very low, if any, against methamphetamine. CONCLUSIONS: Their total absence of effect in several validated animal models of the disease does not support antipsychotic properties of H(3)-receptor inverse agonists. However, their positive effects previously reported in behavioral tasks addressing learning, attention, and memory maintain the interest of H(3)-receptor inverse agonists for the treatment of cognitive symptoms of schizophrenia as adjunctive medications.

Molecular mechanism of hepatitis C virus replicon variants with reduced susceptibility to a benzofuran inhibitor, HCV-796.

HCV-796 selectively inhibits hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase. In hepatoma cells containing a genotype 1b HCV replicon, HCV-796 reduced HCV RNA levels by 3 to 4 log(10) HCV copies/mug total RNA (the concentration of the compound that inhibited 50% of the HCV RNA level was 9 nM). Cells bearing replicon variants with reduced susceptibility to HCV-796 were generated in the presence of HCV-796, followed by G418 selection. Sequence analysis of the NS5B gene derived from the replicon variants revealed several amino acid changes within 5 A of the drug-binding pocket. Specifically, mutations were observed at Leu314, Cys316, Ile363, Ser365, and Met414 of NS5B, which directly interact with HCV-796. The impacts of the amino acid substitutions on viral fitness and drug susceptibility were examined in recombinant replicons and NS5B enzymes with the single-amino-acid mutations. The replicon variants were 10- to 1,000-fold less efficient in forming colonies in cells than the wild-type replicon; the S365L variant failed to establish a stable cell line. Other variants (L314F, I363V, and M414V) had four- to ninefold-lower steady-state HCV RNA levels. Reduced binding affinity with HCV-796 was demonstrated in an enzyme harboring the C316Y mutation. The effects of these resistance mutations were structurally rationalized using X-ray crystallography data. While different levels of resistance to HCV-796 were observed in the replicon and enzyme variants, these variants retained their susceptibilities to pegylated interferon, ribavirin, and other HCV-specific inhibitors. The combined virological, biochemical, biophysical, and structural approaches revealed the mechanism of resistance in the variants selected by the potent polymerase inhibitor HCV-796.

Inhibition of PCDD/F and PCB formation in co-combustion.

Co-combustion of coal-solid waste mixtures in pilot and laboratory-scale combustors with emphasis on monitoring of toxic chlorinated hydrocarbon emissions such as polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) and polychlorinated biphenyls (PCB) is elaborated. The objective of the work is to investigate the so-called primary measures technique. Twenty different thermally resistant inorganic compounds were added directly to the fuel as inhibitors of PCDD/F formation. The fuel-types used in this study included lignite coal, pre-treated municipal solid waste and polyvinyl chloride (PVC). Principle component analysis (PCA) provides the basis for a feasible discussion about the efficiency of 20 inhibitors on PCDD/F and PCB formation. The study showed that the metal oxides group investigated had no inhibitory effect. Although the single N- and S-containing compounds, used as additives for the type of lignite coal, solid waste and PVC fuel, are not very effective as inhibitors, all other N- and S-containing substances are capable to strongly reduce PCDD/F and PCB flue gas emission. The most effective inhibitors are (NH(4))(2)SO(4) and (NH(4))(2)S(2)O(3). (NH(4))(2)SO(4) present at 3% of the fuel can reduce the PCDD/F emissions to 90%. Its low cost and high efficiency favour them as useful for full-scale combustion units.

Lipid peroxidation induced by carbon tetrachloride and its inhibition by antioxidant as evaluated by an oxidative stress marker, HODE.

We have recently proposed total hydroxyoctadecadienoic acid (HODE) as a biomarker for oxidative stress in vivo. The biological samples such as plasma, urine, and tissues were first reduced and then saponified to convert the oxidation products of linoleate to HODE. In the present study, this method was applied to measure the oxidative damage induced by the administration of carbon tetrachloride to mice and also to evaluate the capacity of antioxidant to inhibit the above damage. alpha-Tocopherol transfer protein knock out (alpha-TTP-/-) mice were used to evaluate antioxidant effect in the absence of alpha-tocopherol. The intraperitoneal administration of carbon tetrachloride to mice induced the increase in HODE in liver and plasma, which was followed by an increase in plasma glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT). F2-isoprostanes, another prevailing biomarker, were also increased similarly, but their concentration was approximately two to three orders of magnitude smaller than that of HODE. The lipophilic antioxidants such as gamma-tocopherol, gamma-tocotrienol and 2,3-dihydro-5-hydroxy-4,6-di-tert-butyl-2,2-dipentylbenzofuran (BO-653) were effective in suppressing the formation of HODE.

Interaction with indinavir to enhance systemic exposure of an investigational HIV protease inhibitor in rats, dogs and monkeys.

1. The use of a beneficial interaction between indinavir and compound A, a potent investigational HIV protease inhibitor to enhance systemic exposure of compound A, was investigated. 2. When administrated alone, compound A underwent extensive hepatic first-pass metabolism in rats and monkeys, resulting in low oral bioavailability. 3. In vitro studies with liver microsomes revealed that compound A metabolism was mediated exclusively by CYP3A enzymes in rats, dogs and monkeys. Indinavir, which also was metabolized predominantly by CYP3A enzymes, extensively inhibited compound A metabolism in microsomes, whereas compound A showed weak inhibitory potency on indinavir metabolism. 4. Consistent with in vitro observations, co-administration of the two compounds resulted in a 17-fold increase in oral AUC of compound A in rats owing to the inhibition of metabolism of compound A by indinavir, whereas compound A did not affect indinavir metabolism as indicated by the unchanged indinavir AUC. Similarly, the systemic exposure of compound A in dogs and monkeys was increased substantially following oral co-administration with indinavir by 7- and > 50-fold, respectively. 5. Enhancement in compound A systemic exposure by indinavir in humans, as predicted based on the in vivo animal and in vitro human liver microsomal data, was confirmed in subsequent clinical studies.

Potential serotonergic and noradrenergic involvement in the discriminative stimulus effects of the selective imidazoline I2-site ligand 2-BFI.

The functional significance of imidazoline I2 binding sites is unknown but microdialysis studies have indicated that the administration of I2-site ligands leads to an increase in extracellular levels of monoamines. The specific I2-site ligand 2-(-2-benzofuranyl)-2-imidazoline (2-BFI) generates a cue in drug discrimination, thereby indicating functional consequences of I2-site ligand binding. In the present work, we explored the ability of selective noradrenergic and serotonergic ligands to substitute for 2-BFI. Hooded Lister rats were trained in two-lever operant chambers with condensed milk reward to distinguish 2-BFI (7 mg/kg) from saline vehicle, by pressing the correct lever to a predetermined success criterion. Training sessions were then interspersed with sessions in which animals were administered test substances and the proportion of lever presses on the 2-BFI-associated lever (substitution) recorded. Several agents exhibited significant partial substitution for 2-BFI: The monoamine-releasing agents D-amphetamine and fenfluramine dose-dependently substituted for 2-BFI, while norepinephrine (desipramine, reboxetine) and serotonin (clomipramine, citalopram) reuptake inhibitors substituted at one or more doses. Further investigation using specific receptor agonists and antagonists indicated a possible role for activation of alpha1-adrenoceptors but failed to support involvement of alpha2-adenoceptor, beta-adrenoceptor or 5-HT1A receptor activation. These results support the concept that the 2-BFI cue may contain both noradrenergic and serotonergic components.

Drug therapy options for patients with irritable bowel syndrome.

Existing pharmacotherapeutic options for the treatment of patients with irritable bowel syndrome (IBS) are limited in treating the multiple symptoms associated with the disorder. There is much interest in the use of serotonin agents as new therapeutics. Acting primarily through 5-HT3 and 5-HT4 receptors, serotonin elicits changes in motor function and possibly visceral sensation. Two serotonin agents were developed specifically for IBS: tegaserod, a 5-HT4 receptor partial agonist, and alosetron, a 5-HT3 receptor antagonist (which is no longer available). Phase III clinical trial data show that during a 12-week treatment period with tegaserod, IBS patients with abdominal pain and discomfort, bloating, and constipation experienced significant global relief (i.e., improvement in overall well-being, abdominal pain, and bowel habit) compared with placebo. Improvement in bowel movement frequency and consistency was achieved and pain was relieved by 1 week. During 12 weeks of treatment, alosetron was shown to elicit significant relief of abdominal pain and discomfort compared with placebo or mebeverine in female IBS patients with diarrhea. Alosetron slowed colonic transit and treatment efficacy was apparent after a week of treatment. Another 5-HT4 receptor agonist, prucalopride, which is being developed for chronic constipation, accelerates colonic transit and increases stool frequency. Therefore, this agent may be of benefit in IBS patients with constipation.

Spinal administration of selective opioid antagonists in amphibians: evidence for an opioid unireceptor.

In mammals, opioids act by interactions with three distinct types of receptors: mu, delta, or kappa opioid receptors. Using a novel assay of antinociception in the Northern grass frog, Rana pipiens, previous work demonstrated that selective mu, delta, or kappa opioids produced a potent antinociception when administered by the spinal route. The relative potency of this effect was highly correlated to that found in mammals. Present studies employing selective opioid antagonists, beta-FNA, NTI, or nor-BNI demonstrated that, in general, these antagonists were not selective in the amphibian model. These data have implications for the functional evolution of opioid receptors in vertebrates and suggest that the tested mu, delta, and kappa opioids mediate antinociception via a single type of opioid receptor in amphibians, termed the unireceptor.

Agonist and antagonist effects of dynorphin A-(1-13) in a thermal antinociception assay in rhesus monkeys.

The agonist and antagonist effects of intravenously administered dynorphin A-(1-13) were characterized in the warm water (50 and 55 degrees C) tail withdrawal assay of antinociception in rhesus monkeys. The peptide dose-dependently elevated tail withdrawal latencies in 50 degrees C water, but was ineffective in 55 degrees C water. The antinociceptive effect of dynorphin was surmountably antagonized by quadazocine (0.1 mg/kg) and nor-binaltorphimine (3.2 mg/kg), but was not antagonized by clocinnamox (0.1 mg/kg); this pattern of antagonism is consistent with a kappa-opioid receptor mediated effect. Pretreatment with dynorphin A-(1-13) (0.032-3.2 mg/kg) antagonized the antinociceptive effects of U50,488 and U69,593 in 55 degrees C water, suggesting a low efficacy action of the peptide at the receptors activated by these kappa agonists. However, dynorphin A-(1-13) (3.2 mg/kg) did not antagonize other kappa agonists: bremazocine (0.018-0.056 mg/kg) and enadoline (0.0056-0.018 mg/kg). Taken together, these dynorphin A-(1-13) findings support the notion of functional kappa-opioid receptor subtypes, and it appears that dynorphin A-(1-13) has limited efficacy at one of these sites. Finally, dynorphin A-(1-13) (0.32 mg/kg) also antagonized the antinociceptive effects of the mu-agonist etonitazene (0.0018-0.01 mg/kg).

[In vitro analysis for cellular toxicity of polychlorinated biphenyls(PCBs) and 2, 3, 4, 7, 8-pentachlorodibenzofuran (PCDF) on HeLa cell proliferation(III)--the effect of cytoactivator and antilipemic agents on cell toxicity].

We investigated the cell toxicity of polychlorinated biphenyls (PCBs) and 2, 3, 4, 7, 8-pentachlorodibenzofuran (PCDF) as indicators of the optical density (280nm) which is total protein in HeLa cells. Furthermore, the reductive action of cytoactivator and antilipemic agents on the PCBs and PCDF toxicity were evaluated. The quantity of total cellular protein increased to 20% with the addition of sodium dextran sulfate (2.5%) at the presence of PCBs, and 25% in the case of PCDF. However, the slope of the curve of cell proliferation of HeLa cells at the presence of PCBs or PCDF became to overlap with a control group at the presence of any other drugs except for sodium dextran sulfate. These results mean that PCBs and PCDF cell toxicity were suppressed a little by sodium dextran sulfate, but the case of other cytoactivator and antilipemic agents did not.

Antidotal action of atropine sulfate against insecticide benfuracarb poisoning in rats.

The antidotal action of atropine sulfate and 2-pyridine aldoxime methiodide (2-PAM) against poisoning attributable to the new procarbamate insecticide benfuracarb [(ethyl N-[2,3-dihydro-2,2-dimethylbenzofuran-7-yloxycarbonyl (methyl) aminothio]-N-isopropyl-beta-alaninate] was compared utilizing rats as our experimental model. Both the intraperitoneal and oral administrations of these antidotes were examined after five, ten, fifteen and thirty minutes exposure periods, following treatment with benfuracarb at dose levels approximating LD50 and LD100. The results obtained demonstrate that both the intraperitoneal and oral administrations of atropine sulfate blocked or significantly reduced the toxic effects of benfuracarb and protected the animals from death. The intraperitoneal administration route appears to be more effective than was the oral route. In addition, the administration of atropine sulfate after the shorter period (up to 15 minutes), following exposure to benfuracarb, improved antidotal action, particularly with the LD100 dose of benfuracarb. It is suggested that atropine sulfate antagonizes benfuracarb poisoning by blocking acetylcholine (ACh) receptors, as many other carbamate insecticides, since benfuracarb was an in vivo cholinesterase (ChE) inhibitor and the toxic effect of benfuracarb was reduced by atropine sulfate. 2-PAM, however, did not significantly block or reduce the toxic effects of benfuracarb.

Behavioral effects of 6-methylene naltrexone (nalmefene) in rhesus monkeys.

Nalmefene [17-N-cyclopropylmethyl-3,14-beta-dihydroxy-4,5-alpha-epoxy-6- methylenemorphinan hydrochloride (also NIH 10365)], a 6-methylene derivative of naltrexone, was compared to naltrexone for its behavioral effects in rhesus monkeys. Nalmefene had opioid antagonist actions under all conditions, having a potency similar to that of naltrexone. In morphine-treated monkeys, discriminating between 0.01 mg/kg of naltrexone and saline, nalmefene substituted completely for naltrexone at doses larger than 0.001 mg/kg. The onset of discriminative stimulus effects was similar for nalmefene and naltrexone. A dose of 0.032 mg/kg of either antagonist occasioned > or = 90% naltrexone-level responding beginning 6 to 8 min after s.c. administration; the effects of this dose of either antagonist persisted for more than 1 hr. Like the parent compound naltrexone, nalmefene also antagonized the discriminative stimulus effects of opioid agonists. Nalmefene prevented the discriminative stimulus effects of morphine in monkeys acutely deprived of morphine and antagonized the discriminative stimulus effects of nalbuphine in a separate group of monkeys discriminating between nalbuphine and saline. At the dose of naltrexone and nalmefene that produced an equivalent antagonism of morphine when the antagonist was administered 0.25 hr before morphine (0.01 mg/kg), the duration of antagonist action was < 4 hr and > 6 hr, respectively. Nalmefene also attenuated the antinociceptive effects of the mu agonist alfentanil and the kappa agonist CI-977 [5R-(5,7,8-beta)-N-methyl- N-[7-(1-pyrrolidinyl)1-oxaspiro[4,5]dec-8-yl]-4-benzofuranaceta mide], being 55 times more potent in attenuating the antinociceptive effects of alfentanil as compared to Cl-977.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of the stimulatory effects of efaroxan and glibenclamide in rat pancreatic islets by the imidazoline, RX801080.

1. The imidazoline alpha 2-adrenoceptor antagonist, efaroxan, stimulates insulin secretion from rat isolated islets and antagonizes the ability of diazoxide to inhibit glucose-induced insulin secretion. These effects result from closure of ATP-sensitive potassium channels although the mechanisms involved have not been elucidated. 2. In the present work, we have examined the effects of a close structural analogue of efaroxan, RX801080, in rat isolated islets of Langerhans. RX801080 was found to be ineffective as a stimulator of insulin secretion and did not prevent the inhibition of insulin secretion mediated by diazoxide. 3. RX801080 acted as an antagonist of the actions of several imidazolines (efaroxan, phentolamine and midaglizole) in rat islets. It dose-dependently inhibited the ability of efaroxan to antagonize the effects of diazoxide in islets and also completely inhibited the direct stimulation of insulin secretion mediated by efaroxan. 4. RX801080 also antagonized the effects of the non-imidazoline, ATP-sensitive potassium channel blocker, glibenclamide, in rat islets. It inhibited both the capacity of glibenclamide to stimulate insulin secretion and the ability of glibenclamide to overcome the inhibitory effects of diazoxide in rat islets. 5. Antagonism of glibenclamide responses by RX801080 was not due to inhibition of binding of the sulphonylurea to its receptor on the pancreatic beta-cell. 6. The results suggest that imidazoline compounds and sulphonylureas interact with distinct binding sites on islet cells, but that these sites can interact functionally to control islet cell ATP-sensitive potassium channel activity and insulin secretion.

Functional evidence for multiple receptor activation by kappa-ligands in the inhibition of spinal nociceptive reflexes in the rat.

1. The evidence for kappa-receptor heterogeneity is equivocal. We have now investigated this question by comparing the effects of five putatively selective kappa-agonists. The parameters examined were: the relative potencies in depressing hindlimb flexor muscle reflexes to noxious pinch stimuli in both spinalized and sham-spinalized rats; the reversibility of these effects by naloxone; and the effects on blood pressure. 2. Two types of drug effect was discriminated. One drug group, represented by U-50,488, U-69,593 and PD-117,302, had a potency ratio between sham and spinalized rats approximately 10 fold lower than the other group, which comprised GR103545 and CI-977. 3. Under sham-spinalized conditions, CI-977 and GR103545 at high doses caused only sub-maximal reductions of spinal reflexes. U-50,488 was still active when superimposed on these high doses of GR103545. 4. Naloxone reversed all effects, but different doses were required between compounds, with GR103545 taking some 20 times higher doses of naloxone to cause reversal than did U-50,488. 5. The effects on mean arterial pressure were opposite between groups. 6. The results imply that more than one type of naloxone-sensitive non-mu opioid receptor must be involved in mediating these complex actions of ligands that have been claimed to be selective for kappa-receptors.

Pharmacologic activity of CI-977, a selective kappa opioid agonist, in rhesus monkeys.

CI-977 is a selective, nonpeptide kappa opioid agonist. In rhesus monkeys, CI-977 is a potent antinociceptive agent against thermal stimuli after i.m. administration. Increasing the intensity of the nociceptive stimulus can reduce the analgesic activity of CI-977. Antinociceptive activity also was seen when PD 126212, containing CI-977 as the (-)-enantiomer, was administered sublingually. Naloxone antagonized the antinociceptive action of CI-977, demonstrating opiate receptor involvement in this activity. Monkeys treated with CI-977 also showed sedation at doses close to those required to produce antinociception. As with morphine, the sedative properties of CI-977 were associated with impaired cognitive performance. Aged monkeys appeared more sensitive than young monkeys to the performance-impairing effect of CI-977. Tolerance developed to the antinociceptive and response-suppressing effects. CI-977 was approximately 1000 times more potent than morphine as an analgesic when tested against a moderate (50 degrees C) thermal stimulus but less effective than morphine against a strong (55 degrees C) thermal stimulus.

A highly selective kappa-opioid receptor agonist, CI-977, reduces excitatory synaptic potentials in the rat locus coeruleus in vitro.

Intracellular recordings were made from neurons in a rat locus coeruleus slice preparation in vitro. A postsynaptic potential was evoked by electrical stimulation of afferents to the neurons. CI-977 ([5R-(5a,7a,8b)]-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec -8-yl[-4-benzofuranacetamide monohydrochloride) caused a depression of the evoked postsynaptic potential on locus coeruleus neurons. This action was reversed on washout. Bremazocine had a similar action on less than 50% of locus coeruleus neurons. Concentrations of CI-977 which depressed the postsynaptic potential did not affect either passive membrane conductance or a voltage-sensitive potassium current resembling IA. The depression of the excitatory postsynaptic potential caused by CI-977 remained in the presence of either 30 microM bicuculline and picrotoxin or when potassium acetate-filled recording electrodes were used. Using potassium chloride-filled recording electrodes and in the presence of 30 microM 6-cyano-2,3-dihydro-7-nitroquinoxaline-2,3-dione and either 30 microM DL-2-amino-5-phosphonovaleric acid or 500 microM kynurenic acid, CI-977 had no effect on the postsynaptic potential. The effects of CI-977 were reversed by 30-100 nM naloxone and 1-10 nM norbinaltorphimine but not by 1-10 nM naloxone. The hyperpolarizing response to the mu-opioid receptor-selective agonist D-Ala2,Nme Phe4,Gly-ol5 (DAGOL) was blocked by 1-10 nM naloxone but not by 1-100 nM norbinaltorphimine. The hyperpolarizing response to DAGOL was not affected by high doses of CI-977.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine receptor-mediated spinal antinociception in the normal and haloperidol pretreated rat: effects of sulpiride and SCH 23390.

Nociceptive tail flick latencies (TFL) were recorded in response to noxious thermal stimuli applied to lightly anaesthetized rats. The effects of intrathecally administered dopamine receptor agonists alone and combined with dopamine receptor antagonists were examined upon the TFL. Experiments were repeated on animals made supersensitive to dopamine following withdrawal from 28 day administration of haloperidol. In untreated animals the D2-receptor agonist LY 171555 and apomorphine produced an increase in TFL. In contrast, the Di-receptor agonist SKF 38393 had no significant effect on TFL. TFL. Following haloperidol-induced dopamine-supersensitivity, SKF 38393 produced an increase in TFL. In contrast, LY171555 and apomorphine had minimal effects on TFL in this preparation. In animals not treated with haloperidol, the dopamine receptor antagonists SCH 23390 and (+/-)-sulpiride both blocked the increase in TFL produced by the D2-agonists. SCH23390 and (+/-)-sulpiride also blocked the increase in TFL produced by SKF 38393 in haloperidol-supersensitized animals. The antinociceptive action of intrathecally administered dopamine agonists appears to be mediated via D2-receptors. Whether the antinociception produced by SKF 38393 is exclusively contingent upon the activation of D1-receptors in the dopamine-supersensitive animal is as yet unresolved.