Characterization of GABAB ligands in vivo

• 1.1. While GABA_B antagonists have been examined in vitro, very few have been tested in vivo. A range of GABA_B antagonists were tested against baclofen-induced muscle relaxation and hypothermia.
• 2.2. The GABA_B antagonists exhibited a range of in vivo activity profiles.
• 3.3. CGP 35348 showed clear antagonist effects, while BPBA and 4-ABPA appeared to have agonist properties.
• 4.4. Phaclofen, 2-hydroxysaclofen, 3-APPA and 9G seemed to have little effect in this system at the doses tested.
• 5.5. Differences between in vivo and in vitro activity could be explained by differences in blood-brain barrier permeability, or possible differences in affinities for the sub-classes of GABA_B receptors.

     

Central and peripheral dopamine D1/DA1 receptor modulation of gastric secretion and experimental gastric mucosal injury

• 1.1. Dopamine D₁ (central)/DA₁ (peripheral) receptors are believed to influence gastrointestinal function and pathology.
• 2.2. When given i.c.v. or i.p., an agonist (SKF38393) and an antagonist (SCH23390) of this DA receptor subtype inhibit and enhance, respectively, gastric secretion and gastric mucosal injury.
• 3.3. When given both i.c.v. and i.p., their respective effects in the gut were amplified.
• 4.4. Antagonist or agonist given i.p., blocked the corresponding protective and worsening effect of the agonist or antagonist given i.c.v.
• 5.5. Both central and peripheral D₁/DA₁ receptors modulate gastric function and response to injury.

     

The use of the human neuroblastoma SH-SY5Y to study the effect of second messengers on noradrenaline release

• 1.1. Recent data suggesting that the human neuroblastoma SH-SY5Y is a suitable cell line in which to study the effect of second messengers on NA release are discussed in the context of current views on exocytosis.
• 2.2. Release of NA is evoked by depolarization, as well as activation of muscarinic (M₃) and bradykinin (B₂) receptors in SH-SY5Y cells which have not been differentiated by the addition of growth factors.
• 3.3. Evoked release is enhanced by activation of protein kinase C.
• 4.4. Activation of protein kinase C decreases the changes in intracellular calcium evoked by carbachol, bradykinin and 100 mM K⁺.
• 5.5. SH-SY5Y express N-type and L-type voltage sensitive Ca²⁺ channels. L-Type Ca²⁺-channels are coupled to NA release under conditions of weak depolarization. However with strong depolarization (100 mM K⁺) both L-type and N-type channels are involved.
• 6.6. Muscarinic- and neuropeptide Y receptors are coupled to the inhibition of Ca²⁺ channel activity.

     

Different influences of adenosine receptor agonists and antagonists on morphine antinociception in mice

• 1.1. Subcutaneous (s.c.) administration of morphine to mice induced a dose-dependent antinociception.
• 2.2. Pretreatment of animals with adenosine receptor antagonists NECA (5′-N-ethylcarboxamidermadenosine) and l-PIA (N⁶-phenylisopropyladenosine) potentiated, while adenosine agonist CHA (N⁶-cyclohexyladenosine) decreased the morphine response.
• 3.3. Adenosine antagonist theophylline decreased, but adenosine receptor antagonist 8-PT (8-phenyltheophylline) increased the antinociception effect of morphine. Inhibitory effect of CHA on morphine antinociception was also reversed by 8-PT pretreatment.
• 4.4. NECA or l-PIA induced a high degree of antinociceptive effect in animals pretreated with 8-PT.
• 5.5. Dipyridamole pretreatment did not alter the effect of morphine.
• 6.6. It is concluded that A-1 and/or A-2 adenosine receptors are involved in morphine antinociception and the adenosine mechanism(s) may exert a modulatory role in this respect.

     

Flupirtine,a Nonopioid Centrally Acting Analgesic,Acts as an NMDA Antagonist*

• 1.Flupirtine (Katadolon) is a member of a class of triaminopyridines and is used as a nonopioid analgesic agent with muscle relaxant properties.
• 2.In situ experiments have revealed that flupirtine protects against ischemic-induced insults to the retina and brain.
• 3.Data derived from in vitro and in vivo studies suggest that flupirtine functions as a weak N-methyl-d-aspartate (NMDA) antagonist with little evidence that it acts on AMPA–kainate type glutamate receptors.
• 4.No evidence could be found from binding studies to suggest that flupirtine has an affinity for any of the characterized binding sites associated with the NMDA receptor.
• 5.Studies on cultured cortical neurons show that the NMDA-induced influx of ⁴⁵Ca²⁺ is more readily decreased by flupirtine when a reducing agent (dithiothreitol) is present. However, when N′-ethylmaleimide, which is thought to alkylate the NMDA receptor redox site, is present, no obvious effect on the NMDA-induced influx of ⁴⁵Ca²⁺ is produced by flupirtine.
• 6.Flupirtine is also known to counteract the production of reactive oxygen species caused by ascorbate/iron as well as to prevent apoptosis in cells lacking NMDA receptors induced by oxidative stress.
• 7.To explain all the experimental data, it is suggested that flupirtine affects the redox state/pH/electrons in the cell. The specific way by which flupirtine antagonizes the NMDA receptor might be by an action on the known redox site of the receptor.

     

Neuropharmacology of zonisamide,a new antiepileptic drug

• 1.1. Zonisamide readily crosses the blood-brain barrier and is readily absorbed after oral administration with a T_max of about 3 hr.
• 2.2. The half-life of ZNA in epileptic patients is about 28 hr.
• 3.3. Zonisamide has a broader therapeutic range than other antiepileptic drugs.
• 4.4. Neurotoxic, hemapoietic, renal, and liver effects have been minimal in patients participating in controlled clinical studies.
• 5.5. It is effective in several experimental models of epilepsy and in initial clinical trials has been shown to be effective in generalized tonic-clonic, simple, and complex partial seizures.

     

The CCKA receptor antagonist devazepide inhibits the effect of apomorphine on vasopressin release in pigs

• 1.1. A transient increase in plasma vasopressin concentrations represents a physiological correlate of nausea in animals that vomit.
• 2.2. The CCK_A receptor antagonist devazepide has previously been shown to inhibit vasopressin release induced in pigs by intravenous (i.v.) CCK.
• 3.3. This study investigated whether devazepide (70 μg/kg i.v.) would affect vasopressin secretion induced in pigs (n = 6) by the emetic drug apomorphine (25 μg/kg i.v.).
• 4.4. Apomorphine stimulated vasopressin release in the 30 min period following injection; this effect was prevented by prior administration of devazepide.
• 5.5. The results suggest that CCK_A receptor antagonists may have the ability to prevent nausea and/or emesis.

     

5-HT receptors on identified Lymnaea neurones in culture: Pharmacological characterization of 5-HT3 receptors

• 1.1. The selective agonist, 1-(m-chlorophenyl)-biguanide (m-CPBG) and antagonist, 3-tropanyl-3,5-dichlorobenzoate (MDL 72222) were used to characterize the 5-HT₃ receptors in cultured identified neurones; the serotonin-containing cerebral giant cells (CGCs) and some follower neurones in the buccal ganglia of Lymnaea stagnalis.
• 2.2. 5-HT and its agonists were pressure ejected, while the 5-HT antagonists were bath applied.
• 3.3. Although m-CPBG evoked mostly depolarizing responses, hyperpolarizing responses were sometimes evoked.
• 4.4. At 10⁻⁴ M, m-CPBG failed to mimic the responses of 5-HT, but at a concentration higher. 10⁻³ M, pressure-ejected m-CPBG mimicked most 5-HT responses.
• 5.5. The 5-HT₂ antagonist ketanserin failed to block the m-CPBG-evoked responses, whilst partially blocking the 5-HT responses.
• 6.6. These results suggest the presence of 5-HT₃ receptors similar to those found in mammalian neurones, and that multiple subtypes of these receptors may be present in Lymnaea neurones.

     

Adrenocorticotropin activates glycerol-3-phosphate acyltransferase in bovine adrenal glomerulosa cells

• 1.1. The mechanism whereby ACTH activates the synthesis of diacylglycerol (DAG) in isolated adrenal glomerulosa cells was investigated.
• 2.2. ACTH activates glycerol-3-phosphate acyltransferase (G3PAT) in intact and cell-free preparations of adrenal glomerulosa cells. Whereas activation of G3PAT by ACTH was observed in homogenates and membrane fractions, no activation was observed by angiotensin II (AII) at the same concentration.
• 3.3. ACTH effects were mimicked by nonspecific phospholipase C (PLC).
• 4.4. Our preliminary results suggest that ACTH activation of G3PAT may account for ACTH-induced increases in DAG via de novo synthesis of phosphatidic acid (PA).

     

PEI6, a new basic secretagogue in rat peritoneal mast cells: Characteristics of polyethylenimine PEI6 resemble those of compound 48/80

• 1.1. Polyethylenimine with a molecular weight of 600 (PEI₆) was the simplest and the most useful to investigate mast cell-activating mechanisms via pertussis toxin (IAP)-sensitive G protein pathway.
• 2.2. IAP, lidocaine, or dibutyryl cyclic AMP were inhibitors of the histamine release induced by PEI₆, but anti-allergic drug DSCG, the calcium antagonist, D-600, kinase inhibitors, H-7 and K252a, or the calmodulin inhibitor, W-7 were not.
• 3.3. The additive effects of compound 48/80 and PEI₆ suggested that the action sites for PEI₆ overlapped the binding sites of compound 48/80.
• 4.4. Mast cell activation induced by PEI₆ was sugar-specifically inhibited by N-acetylglucosamine(Glc-NAc)-specific lectins and/or by sialic acid (Sia)-specific lectins, suggesting that the action sites for PEI₆ were glycoproteins having G1cNAc and/or Sia residues.
• 5.5. Four glycoproteins seemed to be involved in histamine release, including the IAP-sensitive G-protein pathway.

     

The in vivo and in vitro protective properties of taurine

• 1.1. Taurine is a ubiquitous, free amino acid found in mammalian systems.
• 2.2. The biological functions of taurine are unclear.
• 3.3. Various in vivo data suggest that taurine has a variety of protective functions and deficiency leads to pathological changes.
• 4.4. Depletion in rats of taurine increases susceptibility to liver damage from carbon tetrachloride.
• 5.5. Susceptibility to a variety of hepatotoxicants correlates with the estimated hepatic taurine level.
• 6.6. In vitro data suggest that taurine can protect cells against toxic damage.
• 7.7. Taurine protects isolated hepatocytes against carbon tetrachloride, hydrazine and 1,4-naphthoquinone but not against allyl alcohol, α-naphthylisothiocyanate (ANIT) or diaminodiphenyl methane (DAPM) cytotoxicity.
• 8.8. The mechanisms of protection are unclear but may include modulation of calcium levels, osmoregulation and membrane stabilization.

     

Enhancement of morphine actions in morphine-naive and morphine-tolerant mice by LY 235959, a competitive antagonist of the NMDA receptor

• 1.1. The effects of LY 235959, a competitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, on the analgesic and hypothermic actions of morphine, were determined in nontolerant and morphine-tolerant mice.
• 2.2. LY 235959 enhanced the analgesic and hypothermic action of morphine in nontolerant mice.
• 3.3. LY 235959 also enhanced the analgesic and hypothermic actions of morphine in morphine-tolerant mice. LY 235959, injected before saline injection, had no effect on the antinociception or the body temperature.
• 4.4. It is concluded that competitive antagonism of the NMDA receptor enhances the pharmacologic actions of morphine both in morphine-naive and morphine-tolerant mice and that these actions differ from the noncompetitive antagonism of the NMDA receptors.

     

Opposite effects of sex steroids on 11β-hydroxysteroid dehydrogenase activity in the normal and adrenalectomized rat testis

• 1.1. Sex steroids have been shown to regulate the biosynthesis of 11β-hydroxysteroid dehydrogenase (11β-HSD).
• 2.2. In vitro studies showed that oestradiol (E2) or testosterone (T) can interfere with the bioassay of enzyme activity, but not progesterone (P4).
• 3.3. For in vivo studies, the activity of 11β-HSD in the testis of normal and adrenalectomized (ADX) adult male Wistar rats was determined following a daily IM injection of sex steriods for 7 days.
• 4.4. The 11β-HSD activity was significantly reduced (P<0.01) either by E2 or T in normal and ADX rats. The enzyme activity in normal rats given both T and E2 was even lower (P<0.001) than when E2 was given alone.
• 5.5. P4 given to normal and ADX rats increased the enzyme activity higher than normal (P<0.001).
• 6.6. The presence of corticosteroids influenced the effects of E2, but not of T and P4, on 11β-HSD activity.
• 7.7. E2 and T downregulate 11β-HSD activity, whereas P4 increased it. E2 did not act through lowering T level.

     

Effects of selective dopamine receptor compounds on single,spontaneously-active neostriatal neurons

• 1.1. The effects of selective dopamine receptor compounds on the spontaneous activity of single neostriatal neurons were examined extracellularly.
• 2.2. Intravenous administration of quinpirole, the D₂ agonist, elicited a dose-dependent depression in discharge rate.
• 3.3. Quinpirole-evoked depression was reversed by the D₂ antagonist eticlopride, but not the D₁ antagonist SCH 23390.
• 4.4. The partial D₁ agonist, SKF 38393 induced depression and excitation in equal proportion.
• 5.5. A dose of 0.25 mg/kg SCH 23390 blocked SKF 38393-induced depression but not excitation.
• 6.6. SKF 38393-induced excitation was antagonized by eticlopride and in some cases by a higher dose of SCH 23390.

     

Interaction of amiloride with rat parotid muscarinic and alpha-adrenergic receptors

• 1.1. In rat parotid acim, amiloride inhibited the secretion of amylase and the efflux of calcium and rubidium in response to carbamylcholine and to norepinephrine.
• 2.2. Amiloride competitively inhibited the binding of [³h]N-methylscopolamine and [³h]is thus a competitive antagonist of muscarinic and norepinephrine α-adrenergic receptors.
• 3.3. Amiloride did not affect the response to substance P with respect to secretion or ion movements.
• 4.4. Thus the Na⁺/H⁺ antiporter is not involved in the short-term regulation of amylase secretion and calcium and potassium movements in rat parotid gland function

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The sigma-selective ligand NE-100 attenuates the effect of phencyclidine in a rat diving model

• 1.1. Phencyclidine (PCP) reduces the latency of rats diving into a water-filled pool from a hidden platform, without stereotyped behavior.
• 2.2. The sigma-selective ligand, NE-100 (N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride), attenuates the effects of PCP in this procedure.
• 3.3. The serotonin₂ (5-HT₂) antagonist, ritanserin, and the sigma receptor ligands, 1-(cyclopropylmethyl)-4-[2′(4″-fluorophenyl)-2'-oxoethyl]-piperidine HBr (Dup734), 4-[2′-(4″-cyanophenyl)-2′-oxoethyl]-1-(cyclopropylmethyl)piperidine (XJ448), α-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMY14802) and rimcazole similarly attenuate the effects of PCP.
• 4.4. The dopamine D₂/sigma ligands, haloperidol and cis-N-(1-benzyl-2-methyl-pyrrolidin-3-yl)-2-methoxy-5-chloro-4-methylaminobenzamide (YM-09151-2) completely reverse the effects of PCP, whereas the same dose ranges of these drugs produce sedation.
• 5.5. The dopamine D₂-selective antagonist, sulpiride, has no apparent effect on the PCP latency to the rat dive.
• 6.6. Thus, PCP-induced diving behavior was improved by sigma ligands and the 5-HT₂ antagonist. This model of negative symptoms in an experimental animal will facilitate experiments on drug treatments for schizophrenia.

     

The relationship between erythrocyte superoxide dismutase activity and plasma levels of some trace elements (Al,Cu, Zn) of dialysis patients

• 1.1. The effect of erythropoietin and some trace elements on superoxide dismutase (SOD) activity of dialysis patients have been studied.
• 2.2. SOD activity of dialysis patients was found to be decreased.
• 3.3. The effect of erythropoietin on SOD activity was not found in vitro.
• 4.4. Plasma and erythrocyte aluminum increased in dialysis patients, but no significant change in plasma copper was found.
• 5.5. Plasma zinc levels of dialysis patients were found to be decreased.
• 6.6. These results suggest that inhibition of erythrocyte SOD activity of dialysis patients may contribute to their anemia.

     

Stimulation of angiotensin subtype 2 receptor reduces basal cGMP levels in the neointima of rat aorta after balloon injury

• 1.1. The association between the stimulation of the angiotensin subtype 2 receptor (AT2-R) and the change in tissue levels of cyclic nucleotide was assessed on neointima formation in rat aorta following aortic balloon injury.
• 2.2. Tissue levels of guanosine 3′,5′-cyclic monophosphate (cGMP) and adenosine 3′,5′-cyclic monophosphate levels (cAMP) in the injured and uninjured aorta was determined by enzyme immunoassay at baseline and again 30 s after administration of 10⁻⁷ M angiotension II.
• 3.3. Injured and uninjured aorta showed no difference in basal levels of cGMP. Angiotension II reduced the basal level of cGMP in the injured aorta only.
• 4.4. This decrease was blocked by a selective AT2-R antagonist (PD123319) and by a nonselective angiotensin II antagonist (angiotensin II antipeptide), but not by a selective angiotensin subtype 1 antagonist (CV-11974).
• 5.5. Stimulation with a selective AT2-R caused no change in the level of cAMP in the injured or uninjured aorta.
• 6.6. Results suggest that stimulation of AT2-R in proliferative neointima leads to a decreased tissue level of cGMP.

     

Hepatobiliary function and toxicity in vitro using isolated hepatocyte couplets

• 1.1. Hepatocyte couplets can be routinely prepared from rat liver to produce a suitable in vitro model for polarized primary cells.
• 2.2. Centrifugal elutriation provides a means of producing enriched subpopulations of periportal and perivenous couplets from the same liver, thus providing a means of studying the influence of zonal heterogeneity on hepatobiliary function.
• 3.3. The maintenance of structural and secretory polarity demonstrated by hepatocyte couplets provides a convenient in vitro system for mechanistic studies of factors both regulatory and adversely affecting hepatobiliary functions.
• 4.4. Couplets are also uniquely appropriate for specific studies of regulation at the biliary pole, on the performance of junctions and on the maintenance and rate of transcytotic movement.
• 5.5. The possibility also exists that effects of an in vivo pre-exposure to agents causing hepatobiliary dysfunction can be assessed in couplets ex vivo.