Prevention of stress-induced gastric ulcers by dopamine agonists in the rat

Dopamine (DA) and DA agonists have been shown to exert a protective role against the formation of duodenal ulcers. The effect of stimulation of DA receptors on the development of stress-induced gastric ulcers is currently unknown. Accordingly, we evaluated the effect of several DA agonists on the development of gastric ulcers induced by 3 h of cold + restraint stress (CRS) in rats. Apomorphine, d-amphetamine, methylphenidate, and threo-dl-p-hydroxymethylphenidate (an hydroxylated analog of methylphenidate), significantly reduced both the incidence and severity of CRS-induced gastric ulcers. The gastric cytoprotection afforded by these agents was dose-related, and completely antagonized by pretreatment with the peripheally acting DA antagonist domperidone. Because domperidone blocks peripheral, but not central, DA receptors, and since the entry of threo-dl-p-hydroxymethylphenidate across the blood-brain barrier into the brain is restricted to a great extent, we conclude that stimulation of peripheral DA receptors is primarily involved in the gastric cytoprotection induced by dopamimetics.The pathogenesis of stress-induced gastric ulcers remains largely unknown, and significant efforts have been made over the last decade to functionally characterize some of the factors involved in the etiology of this disease. Considerable attention has been focused on gastric acid secretion, but its primary role in stress-induced gastric ulcer disease remains uncertain. In fact, agents which effectively inhibit or neutralize gastric acid secretion such as cimetidine or antacids do not necessarily exert protection against stress-induced gastric ulcers (1,2). Moreover, in our original studies with neurotensin, a brain and gastrointestinal peptide, we have found that central administration of this neuropeptide, which completely prevents the development of cold + restraint stress (CRS)-induced gastric ulcers, does not appreciably alter gastric acid secretion (2). These findings support the contention that gastric acid secretion may not be an important factor in the development of this type of gastric ulcer.There is, however, considerable evidence that the automatic nervous system plays an intermediary role in the development of these ulcers (3,4). In this regard, surgical or pharmacological blockade of the vagal (cholinergic) division of the autonomic nervous system prevents the appearance of stress-associated gastric ulcers (5,6). Direct stimulation of catecholamine receptors, or indirect activation via increased sympathetic outflow to the periphery (7,4,8–11) appears to produce a salutary effect of stress-induced gastric ulcers.Szabo and his associates (12, 13, 14) have extensively studied the anti ulcer effects of dopamine (DA) in duodenal ulcer formation. Whether DA also modifies the development of stress-induced gastric ulcers is currently unknown.We have therefore evaluated the effect of selected DA receptor agonists and antagonists on CRS-induced gastric ulcer formation in rats.     

Effect of prostaglandin synthesis inhibitors on neurotensin and sodium salicylate-induced gastric cytoprotection in rats

Sodium salicylate (SA) has been reported to inhibit the formation of gastric ulcerations induced by aspirin, indomethacin, and absolute ethanol. In this study, SA dose-dependently inhibited gastric ulcers induced by three hours of cold-restraint stress (CRS); SA-induced cytoprotection was prevented by both acetylsalicylic acid (aspirin) and indomethacin pretreatment. Neurotensin (NT), which has previously been demonstrated to prevent the development of CRS-induced gastric ulcerations after intracisternal administration, was found to be ineffective in animals pre-treated with aspirin, and with indomethacin, as previously described. These data suggest that in the CRS model both NT- and SA-induced gastric cytoprotection require a functionally intact gastrointestinal prostaglandin synthetic pathway.     

Constituents of human meconium--I. Identification of 3-hydroxy-etianic acids

The monohydroxylated fraction of bile acids of human meconium was analyzed by capillary GC-MS. In the sulfate-glucuronide fraction three saturated, and one unsaturated C20 steroidal acids were found. These acids were identified as 3 alpha-hydroxy-5 alpha-, 3 alpha-hydroxy-5 beta-,3 beta-hydroxy-5 alpha-androstane-17 beta-carboxylic, and 3 beta-hydroxyandrost-5-ene-17 beta-carboxylic based on the unequivocal GC-MS comparison with standards of all possible epimers at C-3, 5 and 17. The amount of the major C20 acid, 3 alpha-hydroxy-5 alpha-androstane-17 beta-carboxylic, in meconium was 0.2 nmol/g, i.e. 5 to 10 times the amount of lithocholic acid. To prevent the oxidation of 21-hydroxy-20-oxopregnanes to C20 acids meconium was extracted in the presence of sodium borohydride. In the absence of this reducing agent the amount of 3 beta-hydroxyandrost-5-ene-17 beta-carboxylic acid was increased and its 17 alpha-epimer could be detected. This indicates partial artifactual formation of this C20 acid from 21-hydroxypregnenolone, which is known to be present in human meconium. The amount of the saturated C20 acids was unaffected by the presence of sodium borohydride in the extraction medium, and their native occurence in human meconium was further confirmed by the absence of their 17 alpha-epimers in extracts obtained both with and without borohydride. The probable metabolic origin of C20 acids in the fetal-placental-maternal unit is discussed.     

The pore domain of the nicotinic acetylcholine receptor: molecular modeling, pore dimensions, and electrostatics.

The pore domain of the nicotinic acetylcholine receptor has been modeled as a bundle of five kinked M2 helices. Models were generated via molecular dynamics simulations incorporating restraints derived from 9-A resolution cryoelectron microscopy data (Unwin, 1993; 1995), and from mutagenesis data that identify channel-lining side chains. Thus, these models conform to current experimental data but will require revision as higher resolution data become available. Models of the open and closed states of a homopentameric alpha 7 pore are compared. The minimum radius of the closed-state model is less than 2 A; the minimum radius of the open-state models is approximately 6 A. It is suggested that the presence of "bound" water molecules within the pore may reduce the effective minimum radii below these values by up to approximately 3 A. Poisson-Boltzmann calculations are used to obtain a first approximation to the potential energy of a monovalent cation as it moves along the pore axis. The differences in electrostatic potential energy profiles between the open-state models of alpha 7 and of a mutant of alpha 7 are consistent with the experimentally observed change in ion selectivity from cationic to anionic. Models of the open state of the heteropentameric Torpedo nicotinic acetylcholine receptor pore domain are also described. Relatively small differences in pore radius and electrostatic potential energy profiles are seen when the Torpedo and alpha 7 models are compared.     

Enhancement of anaphylactic mediator release from guinea-pig perfused lungs by fatty acid hydroperoxides

Fragments of chopped lung from indomethacin treated guinea-pigs had an anti-aggregating effect when added to human platelet rich plasma (PRP), probably due to the production of prostacyclin (PGI₂) since the effect was inhibited by 15-hydroperoxy arachidonic acid (15-HPAA, 10 μg ml^?1). Both 15-HPAA (1–20 μg ml^?1 min^?1) and 13-hydroperoxy linoleic acid (13-HPLA, 20 μg ml^?1 min^?1) caused a marked enhancement of the anaphylactic release of histamine, slow-reacting substance of anaphylaxis (SRS-A) and rabbit aorta contracting substance (RCS) from guinea-pig isolated perfused lungs. This enhancement was not reversed by the concomitant infusion of either PGI₂ (5 μg ml^?1 min^?1) or 6-oxo-prostaglandin F_1α (6-oxo-PGF_1α, 5 μg ml^?1 min^?1). Anaphylactic release of histamine and SRS-A from guinea-pig perfused lungs was not inhibited by PGI₂ (10 ng - 10 μg ml^?1 min^?1) but was inhibited by PGE₂ (5 and 10 μg ml^?1 min^?1). Antiserum raised to 5,6-dihydro prostacyclin (PGI₁) in rabbits, which also binds PGI₂, had no effect on the release of anaphylactic mediators. The fatty acid hydroperoxides may enhance mediator release either indirectly by augmenting thromboxane production or by a direct effect on sensitized cells. Further experiments to distinguish between these alternatives are described in the accompanying paper (27).     

The mechanism of enhancement by fatty acid hydroperoxides of anaphylactic mediator release.

Indomethacin augmented the release of histamine and SRS-A but abolished synthesis of TxB2. Compound CLI that inhibited both cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism did not augment release of anaphylactic mediators. 13-HPLA enhanced mediator release from lungs in which arachidonic acid metabolism was blocked by compount CLI. Thus, it is concluded that 13-HPLA enhances mediator release not by altering the balance of arachidonic acid metabolites, e.g. by inhibiting synthesis of prostacyclin, but by a direct effect on lung mast cells. A corollary to this conclusion is that the fatty acid hydroperoxide (HPETE) formed by lipoxygenase from arachidonic acid may also augment the release of anaphylactic mediators. Thus, the enhancement of mediator release by indomethacin may be attributed to increased synthesis of HPETE following inhibition of cyclo-oxygenase.     

Interaction of neurotensin with prostaglandin E2 and prostaglandin synthesis inhibitors: effects on colonic temperature in mice

Neurotensin (NT) administered intracisternally (i.c.) to adult mice produced a marked hypothermia while prostaglandin E₂, administered by the same route, produced hyperthermia. When administered concurrently the effects of the two substances were neutralized. The prostaglandin synthesis inhibitors, indomethacin and acetylsalicylic acid, were injected subcutaneously 30 min prior to i.c. administered NT and/or thyrotropin-releasing hormone (TRH). Both inhibitors failed to potentiate the hypothermia induced by NT or alter its antagonism by TRH in mice kept at 26°C. When mice were kept at 6°C, pretreatment with indomethacin, but not acetylsalicylic acid, potentiated NT-induced hypothermia and prevented its antagonism by TRH. Because indomethacin inhibits synthesis of prostaglandins within the central nervous system (CNS) as well as in peripheral organs while acetylsalicylic acid acts only in the periphery, it appears that NT-induced hypothermia in a cold environment is enhanced by a reduction of prostaglandins in the CNS.     

QSAR modeling and transmission electron microscopy stereology of altered mitochondrial ultrastructure of white blood cells in patients diagnosed as schizophrenic and treated with antipsychotic drugs.

Treatment of patients diagnosed as schizophrenic with antipsychotic drugs (neuroleptics) is known to cause occasional unexplained depletion of white blood cells, especially neutrophil granulocytes. It has been known for many years that neuroleptics can interfere with the mitochondrial respiratory chain in vitro. Because there has been a growing interest recently in mitochondrial targeting of drugs, and since a quantitative structure-activity relationship (QSAR) model that predicts mitochondrial accumulation of neuroleptics has been published, we investigated the effects of neuroleptics on white blood cell mitochondria. Venous blood samples were collected from both patients undergoing treatment with neuroleptics and healthy volunteers. The samples were processed for transmission electron microscopy. The resulting images of white blood cells were analyzed using stereology to compare quantitatively mitochondrial morphology in the patient and control groups. We found that in patients, but not in controls, there was swelling of mitochondria and fragmentation of the mitochondrial cristae. There also were fewer mitochondria in patients than in controls, although due to the swelling of the organelles, the volume density of mitochondria in the two groups was not significantly different. Such changes are typical of a toxic insult. Consequently, it seems plausible that, since schizophrenia is not a disease considered to affect white blood cells per se, these changes probably are due to the medication.     

The MIF Antagonist ISO-1 Attenuates Corticosteroid-Insensitive Inflammation and Airways Hyperresponsiveness in an Ozone-Induced Model of COPD

Introduction

Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine associated with acute and chronic inflammatory disorders and corticosteroid insensitivity. Its expression in the airways of patients with chronic obstructive pulmonary disease (COPD), a relatively steroid insensitive inflammatory disease is unclear, however.

Methods

Sputum, bronchoalveolar lavage (BAL) macrophages and serum were obtained from non-smokers, smokers and COPD patients. To mimic oxidative stress-induced COPD, mice were exposed to ozone for six-weeks and treated with ISO-1, a MIF inhibitor, and/or dexamethasone before each exposure. BAL fluid and lung tissue were collected after the final exposure. Airway hyperresponsiveness (AHR) and lung function were measured using whole body plethysmography. HIF-1α binding to the Mif promoter was determined by Chromatin Immunoprecipitation assays.

Results

MIF levels in sputum and BAL macrophages from COPD patients were higher than those from non-smokers, with healthy smokers having intermediate levels. MIF expression correlated with that of HIF-1α in all patients groups and in ozone-exposed mice. BAL cell counts, cytokine mRNA and protein expression in lungs and BAL, including MIF, were elevated in ozone-exposed mice and had increased AHR. Dexamethasone had no effect on these parameters in the mouse but ISO-1 attenuated cell recruitment, cytokine release and AHR.

Conclusion

MIF and HIF-1α levels are elevated in COPD BAL macrophages and inhibition of MIF function blocks corticosteroid-insensitive lung inflammation and AHR. Inhibition of MIF may provide a novel anti-inflammatory approach in COPD.     

Intellectual property, genetically modified crops and bioethics

The implementation of a new technology is almost always surrounded by a debate on the moral and social implications that may arise. The debate with regard to genetically modified (GM) crops has been one of the longest and most controversial. However, one area of the debate that receives less attention is the role that intellectual property can play. The introduction of an effective and yet appropriate intellectual property system addressing society's particular needs can eliminate some of these issues. This paper looks at whether the situation in Europe is meeting our current needs and also addresses the role intellectual property can play in the debate over the introduction of GM crops in developing countries.