Ostreolysin induces sustained contraction of porcine coronary arteries and endothelial dysfunction in middle- and large-sized vessels

Ostreolysin (Oly), a cytolytic and cardiotoxic protein from the oyster mushroom (Pleurotus ostreatus), is lethal for mice with an LD₅₀ of 1170 μg/kg following intravenous application. Its cardiotoxicity is associated with hyperkalemia, which is probably a consequence of potassium released from the lysed cells. Moreover, sub-micromolar concentrations of Oly induce a concentration-dependent increase in rat aortic ring tension, suggesting that ischaemia, and consequent hypoxic injury of cardiomyocytes, could also derive from vasospasm induced by this toxic protein.The purpose of the present study was to demonstrate histopathological lesions caused by Oly after parenteral application to rats, and to define the mechanisms of Oly-induced vasoconstriction using inhibitors verapamil, lanthanum chloride, and selective endothelin receptor antagonist TBC3214, which have different molecular targets, in vitro on porcine coronary artery rings. We found that Oly causes endothelial injury with perivascular oedema in the heart and lungs, as well as myocardial haemorrhages in rats. Treatment of porcine coronary artery rings with Oly causes concentration-dependent vasoconstriction and prevents endothelium-mediated relaxation. Using TBC3214 as a selective blocker of the endothelin A receptor, we showed that vasoconstriction induced by Oly was independent of endothelin release and its effects. Verapamil (1 μM) greatly reduced Oly-evoked contractions of porcine coronary artery rings, while lanthanum abolished them completely. These results provide evidence that the contraction of coronary arteries by Oly is due mainly to the increased influx of Ca²⁺ from the extracellular space through voltage-dependent L-type Ca²⁺ channels and cation non-selective channels. Experiments suggest that Oly damages endothelial cells both in vitro and in vivo, and probably exhibits direct contractile effects on coronary smooth muscle cells.     

In vivo toxic and lethal cardiovascular effects of a synthetic polymeric 1,3-dodecylpyridinium salt in rodents

APS12-2 is one in a series of synthetic analogs of the polymeric alkylpyridinium salts isolated from the marine sponge Reniera sarai. As it is a potential candidate for treating non small cell lung cancer (NSCLC), we have studied its possible toxic and lethal effects in vivo. The median lethal dose (LD₅₀) of APS12-2 in mice was determined to be 11.5 mg/kg. Electrocardiograms, arterial blood pressure and respiratory activity were recorded under general anesthesia in untreated, pharmacologically vagotomized and artificially ventilated rats injected with APS12-2. In one group, the in vivo effects of APS12-2 were studied on nerve-evoked muscle contraction. Administration of APS12-2 at a dose of 8 mg/kg caused a progressive reduction of arterial blood pressure to a mid-circulatory value, accompanied by bradycardia, myocardial ischemia, ventricular extrasystoles, and second degree atrio-ventricular block. Similar electrocardiogram and arterial blood pressure changes caused by APS12-2 (8 mg/kg) were observed in animals pretreated with atropine and in artificially ventilated animals, indicating that hypoxia and cholinergic effects do not play a crucial role in the toxicity of APS12-2. Application of APS12-2 at sublethal doses (4 and 5.5 mg/kg) caused a decrease of arterial blood pressure, followed by an increase slightly above control values. We found that APS12-2 causes lysis of rat erythrocytes in vitro, therefore it is reasonable to expect the same effect in vivo. Indeed, hyperkalemia was observed in the blood of experimental animals. Hyperkalemia probably plays an important role in APS12-2 cardiotoxicity since no evident changes in histopathology of the heart were found. However, acute lesions were observed in the pulmonary vessels of rats after application of 8 mg/kg APS12-2. Predominant effects were dilation of interalveolar blood vessels and lysis of aggregated erythrocytes within their lumina.     

Remarkable difference in accumulation of paralytic shellfish poisoning toxins among bivalve species exposed to Pyrodinium bahamense var. compressum bloom in Masinloc Bay, Philippines.

Seasonal variation of bivalve toxicity was monitored in association with the abundance of the toxic dinoflagellate Pyrodinium bahamense var. compressum in Masinloc Bay, Luzon Island. Among 7 species of bivalve, 6 species became toxic during a bloom of the dinoflagellate. However, remarkable difference in the toxicity was observed among the species. The toxicity of thorny oyster Spondylus squamosus was the highest among the species, showing more than 30 times that of safety consumption level after the peak bloom of the dinoflagellate, while other bivalve species showed much lower toxicity. The toxicity of thorny oyster decreased under absence of the dinoflagellate, but this species maintained a considerably high toxicity throughout a year. Similar trend was observed in penshell Atrina vexillum in a small scale, indicating that these species in the bay are not safe for human consumption almost throughout a year. The toxicity of green mussel Perna viridis increased to significant level during a bloom, but it decreased rapidly when the dinoflagellate disappeared. Toxin analysis of cultured and natural cells showed typical toxin profile of the dinoflagellate. Toxin profile of all the bivalve species reflected the characteristic toxin profile of the dinoflagellate.     

A neurotoxic phospholipase A2 variant: isolation and characterization from eastern regional Indian cobra (Naja naja) venom.

CM-Sephadex C-25 column chromatography profile of Indian cobra (Naja naja) venom from eastern region showed a distinct and a dominant phospholipase peak, peak-10, while it was not seen in either southern or western venom samples. Peak-10 was subjected to CM-Sephadex C-25 and Sephadex G-50 column chromatography to isolate NN-X-PLA(2). NN-X-PLA(2) is a single chain protein with the relative molecular weight of 10kDa by SDS-PAGE. It was toxic to mice with an LD(50) value 0.098 mg/kg body weight (i.p.) and the mice exhibited acute neurotoxic symptoms. Upon indirect stimulation, it inhibited the twitching of frog's gastrocnemius muscle in a dose dependent manner. NN-X-PLA(2) was weakly anticoagulant and devoid of cytotoxicity, myotoxicity, hemorrhage, edema inducing, and directlytic activities and effects on platelet aggregation process. Upon chemical modification independently with p-bromophenacyl bromide and acetic anhydride, NN-X-PLA(2) lost both enzymatic and toxic properties.     

Monitoring of brevetoxins in the Karenia brevis bloom-exposed Eastern oyster (Crassostrea virginica).

Brevetoxin uptake and elimination were examined in Eastern oyster (Crassostrea virginica) exposed to recurring blooms of the marine alga Karenia brevis in Sarasota Bay, FL, over a three-year period. Brevetoxins were monitored by in vitro assays (ELISA, cytotoxicity assay, and receptor binding assay) and LC-MS, with in vivo toxicity of shellfish extracts assessed by the traditional mouse bioassay. Measurements by all methods reflected well the progression and magnitude of the blooms. Highest levels recorded by mouse bioassay at bloom peak were 157 MU/100g. Oysters were toxic by mouse bioassay at levels >or=20 MU/100g for up to two weeks after bloom dissipation, whereas brevetoxins were measurable by in vitro assays and LC-MS for several months afterwards. For the structure-based methods, summed values for the principal brevetoxin metabolites of PbTx-2 (cysteine and cysteine sulfoxide conjugates), as determined by LC-MS, were highly correlated (r(2)=0.90) with composite toxin measurements by ELISA. ELISA and LC-MS values also correlated well (r(2)=0.74 and 0.73, respectively) with those of mouse bioassay. Pharmacology-based cytotoxicity and receptor binding assays did not correlate as well (r(2)=0.65), and were weakly correlated with mouse bioassay (r(2)=0.48 and 0.50, respectively). ELISA and LC-MS methods offer rapid screening and confirmation, respectively, of brevetoxin contamination in the oyster, and are excellent alternatives to mouse bioassay for assessing oyster toxicity following K. brevis blooms.     

Toxicity and mAChRs binding activity of Cassiopea xamachana venom from Puerto Rican coasts.

A separation of toxic components from the upside down jellyfish Cassiopea xamachana (Cx) was carried out to study their cytotoxic effects and examine whether these effects are combined with a binding activity to cell membrane receptors. Nematocysts containing toxins were isolated from the autolysed tentacles, ruptured by sonication, and the crude venom (CxTX) was separated from the pellets by ultracentrifugation. For identifying its bioactive components, CxTX was fractionated by gel filtration chromatography into six fractions (named fraction I-VI). The toxicity of CxTX and fractions was tested on mice; however, the hemolytic activity was tested on saline washed human erythrocytes. The LD50 of CxTX was 0.75 microg/g of mouse body and for fraction III, IV and VI were 0.28, 0.25 and 0.12 microg/g, respectively. Fractions I, II and V were not lethal at doses equivalent to LD50 1 microg/g. The hemolytic and phospholipase A2 (PLA2) activities of most fractions were well correlated with their mice toxicity. However, fraction VI, which contains the low molecular mass protein components (< or =10 kDa), has shown no PLA2 activity but highest toxicity to mice, highest hemolytic activity, and bound significantly to the acetylcholine muscarinic receptors (mAChRs) isolated from rat brain. The results suggested that fraction VI contains proteinaceous components contributing to most of cytolysis as well as membrane binding events. Meanwhile, fraction IV has shown high PLA2 that may contribute to the venom lethality and paralytic effects.     

Equinatoxin, a lethal protein from Actinia equina. II. Pathophysiological action

Effects of lethal doses of a toxic protein from Actinia equina were studied on anesthetized rats. The electrical activity of the phrenic nerves, the respiratory movements, the mechanical activity of the heart, the ECG, and the arterial blood pressure on intact, vagotomized and artificially respired animals were recorded. Shortly (15–50 sec) after beginning the i.v. injection of equinatoxin, the trains of action potentials in the phrenic nerve disappeared and respiration stopped. Bradycardia was observed, indicating elevated vagal tone. A transient fall of arterial blood pressure in vagotomized and in intact animals was registered for 10–15 sec, simultaneously with the block of respiration; thereafter an elevation of arterial blood pressure was registered for 3–7 min. The elevation of the arterial blood pressure was also observed in artificially respired animals. No spontaneous respiratory movements were registered during the period of elevated arterial blood pressure. The diaphragm remained excitable when stimulated indirectly via the phrenic nerve. Conduction disturbances, ectopic foci, myocardial ischemia, negative inotropic and negative chronotropic actions were followed on the ECG and on the in situ exposed heart.     

Comparative evaluation of acute toxicity of ivermectin by two methods after single subcutaneous administration in rats

Ivermectin was evaluated for its acute toxicity after single subcutaneous (s/c) administration by 'Acute Toxic Class' method as per OECD 423 and by conventional acute toxicity test using probit analysis in rats. 'Acute toxic class' method yielded LD(50) in category 2 i.e. between 5 and 50mg/kg which was comparable with conventional method where it was found to be 51.5mg/kg. Post mortem lesions were observed in the form of congestion of liver, which showed centrilobar necrosis and hemorrhages on histopathological analysis in both the methods. This study suggests, 'Acute Toxic Class' method may be used instead of conventional method to study acute toxicity of injectable preparations. Similarly the LD(50) of around 50mg/kg indicated a wide margin of safety (250x) considering therapeutic dose of ivermectin as 200microg/kg.     

Purification and characterization of antitoxic proteins from the serum of Agkistrodon halys Pallas.

In this study, the authors report the purification and characterization of antitoxic proteins from the serum of Agkistrodon halys Pallas. Two antitoxic proteins have been successfully isolated by the methods of (NH4)(2)SO(4) fractional precipitation, chromatography and preparative discontinuous polyacrylamide gel electrophoresis (PAGE). We have measured their molecular weights by Sephadex G-150 chromatography and 0.1% SDS-Tris-HCl discontinue PAGE respectively. Antitoxin I was about 138,000+/-40 Da and antitoxin II was about 76,000+/-40 Da, they are all single-chain peptides. We have measured their capacity to neutralize the toxicity of agkistrodotoxin (ATX), and their capacity to inhibit the PLA(2) activity of ATX. The results showed that antitoxin I could increase LD(50) of ATX from 0.25+/-0.05 to 0.445+/-0.13 mg/kg, decrease its PLA(2) activity from 2.36 to 1.72 microm/mg min, and antitoxin II could increase LD(50) of ATX from 0.25+/-0.05 to 0.56+/-0.12 mg/kg, decrease Phospholipase A(2) (PLA(2)) activity from 2.36 to 1.2 microm/mg min. When the natural antitoxins were mixed with different amounts of ATX and inoculated intraperitonially into eight mice, it was found that 0.5 mg antitoxin I could neutralize the toxicity of 0.4 mg ATX and 0.5 mg antitoxin II could neutralize the toxicity of 0.5 mg ATX completely. These antitoxic proteins could neutralize the toxicity of ATX completely and inhibit ATX's PLA(2) activity partially.     

Lack of effect of single high doses of buprenorphine on arterial blood gases in the rat.

High dose buprenorphine, a potent semisynthetic agonist-antagonist for opiate receptors, is now used in substitution treatment of human heroin addiction. Deaths have been reported in addicts misusing buprenorphine. We determined the median lethal dose (LD(50)) and studied the effects of high doses of intravenous buprenorphine on arterial blood gases in rats. Male Sprague-Dawley rats were administered buprenorphine intravenously to determine the LD(50) using the up-and-down method. Subsequently, catheterized groups of 10 restrained rats received no drug, saline, acid-alcohol aqueous solvent (required to dissolve buprenorphine at a high concentration), or 3, 30, or 90 mg/kg of buprenorphine intravenously. Serial arterial blood gases were obtained over 3 h. The LD(50) determined in triplicate was 146.5 mg/kg (median of 3 series, range: 142.6-176.5). The mean dose received by surviving animals was 96.9 +/- 46.7 mg/kg. There was a significant effect of the acid-alcohol aqueous solvent on arterial blood gases. Excluding the solvent effect, 3, 30, and 90-mg/kg buprenorphine doses had no significant effects on arterial blood gases. The toxicity of intravenous buprenorphine in adult rats, assessed by the LD(50), is low. These data are consistent with a wide margin of safety of buprenorphine. The mechanism of death after the intravenous administration of a lethal dose of buprenorphine remains to be determined.     

Expression, purification and characterization of the Cry2Aa14 toxin from Bacillus thuringiensis subsp. kenyae

An indigenous strain HD-550 of Bacillus thuringiensis subsp. kenyae was found to be toxic to lepidopteran as well as dipteran insects. The cry2Aa gene (classified as cry2Aa14) from this isolate was cloned and expressed in Escherichia coli. Only a little amount of the expressed Cry2Aa14 protein was observed in soluble fraction under normal induction condition. The inclusions were non-toxic to test insects, whereas solubilized Cry2Aa14 was highly toxic to lepidopteran and dipteran insects. Cry2Aa14 protein was expressed as thioredoxin (trx) fusion protein for improving the yield of active protein. An enhancement of nearly 15% was observed in the yield of active Cry2Aa14. The TrxA-Cry2Aa14 protein purified from the solubilized fraction also showed toxicity profile similar to the wild-type protein. The LC₅₀ values of Cry2Aa14 and TrxA-Cry2Aa14 protein against Spodoptera litura was 694 and 696 ng/cm², respectively, while for Culex quinquefasciatus the LC₅₀ values were 894 and 902 ng/ml, respectively. The broad spectrum toxicity of the Cry2Aa14 thus indicates that this protein could be an important component in integrated pest management. Further, the trx tag clearly led to higher yield, which facilitates protein purification for biophysical and biochemical characterization.     

Studies on the mechanism of action of clonidine after pretreatment with reserpine (author's transl)

The effects of 3.7--30 micrograms 2-(2,6-dichlorophenolamino)-2-imidazoline hydrochloride (clonidine)/kg i.v. on the arterial blood pressure and the central nervous activities of the sympathetic and the phrenic nerves were studied in 33 anaesthetized, relaxed and artificially respirated cats. In part of the experiments the animals were pretreated with reserpine at a dosage of 2X0.3 mg/kg. In normal animals clonidine caused a fall in blood pressure, a reduction of nicotinic pressure effect and an inhibition of sympathetic activity. In pretreated animals the antinicotinic as well as the sympathetic inhibitory actions of clonidine were significantly increased at a dosage of 30 micrograms/kg. The single application of reserpine caused no changes of these two parameters. As a result clonidine probably caused a stimulation of central nervous postsynaptic alpha-adrenoceptors and after the pretreatment with reserpine in addition to this an inhibition of the release of epinephrine.     

Biological properties of the venom from the scorpionfish (Scorpaena plumieri) and purification of a gelatinolytic protease.

In this work we describe some biological properties and a partial biochemical characterization of the Scorpanea plumieri crude venom. The fresh venom induced a decrease in blood pressure, cardiac and respiratory frequency, and exhibited hemorrhagic, hemolytic and proteolytic activities. The LD(50) (i.v. mouse) was 0.28 mg/kg. The pharmacological activities were found to be very unstable and this fact could be associated with proteolytic activity. Enzymes which hydrolyze casein and gelatin were found in this venom. A gelatinolytic protease (Sp-GP) was purified to homogeneity from S. plumieri venom through a combination of three chromatographic steps: gel filtration on Sephacryl S-200; ion exchange on DEAE-cellulose and reverse-phase/HPLC on a Vydac C4 column. The purified protease was approximately 2% of the whole protein in the soluble crude venom. The molecular mass of the Sp-GP scorpionfish gelatinase estimated by SDS-PAGE was around 80,000 Da under reducing conditions and 72,000 Da under non-reducing conditions. Attempts to determine the N-terminal sequence by automatic Edman degradation were unsuccessful, probably due to blockage of the N-terminal group. Gelatinolytic activity was optimal at pH 7-8. This is the first report of the isolation and characterization of a scorpionfish venom protease.     

Venom lethality and diet: Differential responses of natural prey and model organisms to the venom of the saw-scaled vipers (Echis)

The composition of snake venoms shows a high degree of variation at all taxonomic levels, and natural selection for diet has been implicated as a potential cause. Saw-scaled vipers (Echis) provide a good model for studying this phenomenon. The venoms of arthropod feeding species of Echis are significantly more toxic to natural scorpion prey than those of species which feed predominantly upon vertebrate prey. Although testing venom activity on natural prey is important for our understanding of the evolution of venom, natural prey species are often difficult to obtain in sufficient numbers for toxinological work. In order to test the viability of using cheaper and more easily available model organisms for toxicity assessments in evolutionary research, and the extent to which toxicity of arthropod-eating Echis venoms is increased to arthropods in general or targeted to certain groups, we conducted median lethal dosage (LD₅₀) and time to death trials using the desert locust (Schistocerca gregaria) as a model arthropod, rarely consumed by wild Echis. The venoms of arthropod specialist Echis were found to be significantly more toxic to locusts than the venom of a vertebrate feeding outgroup (Bitis arietans), and one arthropod specialist venom was found to be more toxic than those species which feed upon arthropods infrequently or not at all. The venoms of arthropod specialists were also found to cause death and incapacitation faster than the vertebrate feeding outgroup. Despite some similarity of trends, there are considerable differences between the response of natural prey (scorpions) and a model arthropod (locust) to the venoms of Echis species. This suggests that when possible, natural prey rather than convenient model organisms should be used to gain an understanding of the functional significance of variation in venom composition in snakes.     

Effect of mouse strain and gender on LD(50) of yessotoxin

The aim of the present study was to determine whether the intraperitoneal LD(50) for yessotoxin (YTX) in mice varies with strain or gender. Thirty-six male and 36 female mice, of body weight 16-20g, from each of the strains ICR (CD-1), Swiss (CFW-1) and NMRI were employed. They were not fasted before YTX treatment. At each dose, nine mice were injected with YTX solutions at 1.0mL/20g body weight, and observed for 24h. Symptoms and time to death were recorded. Within each mouse strain and gender arm, the study was performed as a basic four level Response Surface Pathway designed trial with nine mice at each dose level. YTX was isolated from a culture of Protoceratium reticulatum. The LD(50) values for female and male mice, respectively, were estimated as 380 and 462mug/kg for the ICR, 269 and 328mug/kg for the Swiss, and 314 and 412mug/kg for the NMRI strains. The increases in LD(50) from female to male mice were found to be 22% for ICR, 22% for Swiss and 31% for NMRI. The largest difference in LD(50) among mouse strains was detected between the ICR and Swiss strains, where the deviation was 41% in both females and males. The difference between mouse strains was found significant (p=0.03). For all three strains, females were more susceptible than males, with a difference in LD(50) of 1.2-1.3-fold. The largest difference between the least- and most-susceptible strain was 1.4-fold for both females and males. The largest difference in LD(50), 1.7-fold, was observed between female Swiss and male ICR mice. The difference between genders was not significant (p=0.12). These results indicate that other factors, like handling of the animals, and the source and handling of the toxin, may significantly influence the outcome of studies on acute toxicity since the reported differences in LD(50) vary by a factor of about seven.     

Toxicity ranking of heavy metals with screening method using adult Caenorhabditis elegans and propidium iodide replicates toxicity ranking in rat

The utility of any model system for toxicity screening depends on the level of correlation between test responses and toxic reactions in humans. Assays in Caenorhabditis elegans can be fast and inexpensive, however few studies have been done comparing toxic responses in this easily cultured nematode with data on mammalian toxicity. Here we report that a screening assay for acute toxicity, using adult C. elegans grown in axenic liquid culture, replicated LD50 toxicity ranking in rat for five metals. This assay utilized the COPAS Biosort and propidium iodide (PI) as a fluorescent indicator of morbidity and mortality after 30-h exposures. We found that chronic toxicity assays of 2-week treatment duration, followed by analysis of PI induced red fluorescence levels, produced less consistent results than the acute assays. However, other chronic toxicity endpoints were compound and concentration specific, including changes in vulval and gonadal morphology, intestinal thickness and integrity, and the presence of retained internal eggs in post-reproductive animals. Some of these endpoints reflect similar findings in mammals, indicating that measurements of morbidity and mortality in conjunction with morphology analyses in C. elegans may have the potential to predict mammalian toxic responses.     

Acute toxicity of methyl isocyanate, administered subcutaneously in rabbits: changes in physiological, clinico-chemical and histological parameters

Subcutaneous administration of methyl isocyanate (MIC) in 0.5 LD50 and 1 LD50 doses in female rabbits resulted in significant changes in physiological, clinico-chemical and histological parameters. There was a fall in arterial blood pressure and cardioacceleration in both the 0.5 LD50 and 1 LD50 groups, while the respiration showed a differential response in these groups with the former showing hyperpnoea and the latter showing respiratory inhibition. A significant increase in the arterial blood lactic acid, lactate/pyruvate ratio and 2,3-diphosphoglycerate levels, and the significant changes in acid-base status of both arterial and venous blood indicated tissue hypoxia of a stagnant type. Histopathological observations revealed a mild to moderate degree of congestion, focal lymphocytic infiltrations and necrosis in all visceral organs examined. These findings suggest that acute toxicity of MIC in vivo may be mediated by its effects on vascular beds.     

Toxicity assessment of crude and partially purified extracts of marine Synechocystis and Synechococcus cyanobacterial strains in marine invertebrates

Among the Cyanoprokaryota, the genera Synechocystis and Synechococcus have rarely been studied with respect to potential toxicity. This is particularly true with marine environments where studies about the toxicity of cyanobacteria are restricted to filamentous forms at the warmer temperate and tropical regions and also to filamentous forms at cold seas such as the Baltic Sea. In this study, we describe the effects of cyanobacterial strains of the Synechocystis and Synechococcus genera isolated from the marine coast of Portugal, on marine invertebrates. Crude and partially purified extracts at a concentration of 100 mg/ml of freeze-dried material of the marine strains were tested for acute toxicity in nauplii of the brine shrimp Artemia salina, in the rotifer Brachionus plicatillis and in embryos of the sea urchin Paracentrotus lividus and the mussel Mytilus galloprovincialis. The cyanobacterial extracts, especially the crude extract, had an impact on A. salina nauplii. No significant toxic effects were registered against the rotifer. A negative impact of all strains was recorded on the embryonic development of the sea urchin, with toxic effects resulting in an inhibition of embryogenesis or development of smaller larvae. To the mussel embryos, the effects of cyanobacterial extracts resulted in a complete inhibition of embryogenesis. The results of all assays indicate that Synechocystis and Synechococcus marine strains contained toxic compounds to marine invertebrates.     

Cytotoxic proteins of Amanita virosa Secr. mushroom: Purification, characteristics and action towards mammalian cells

A new hemolytic lectin was purified from the fruit bodies of Amanita virosa Secr. mushroom by the affinity chromatography on the cross-linked ovomucin. This lectin destroyed erythrocytes of human and animals of various species, and its hemolytic activity decreased in the row: rabbit > rat > human > dog. The erythrocytes of sheep, cow and carp were resistant to such hemolytic action of the lectin (1 mg/mL). The lectin-mediated hemolysis was blocked by the polyethylene glycol with molecular mass over 1350. A. virosa lectin, unlike Amanita phalloides lectin, did not interact with tested monosaccharides. However, the 4-nitrophenyl derivates of the monosaccharides inhibited the action of A. virosa lectin which did not prefer targeting O-type glycoproteins over the N-type glycoproteins. Murine leukemia cells of L1210 line and human leukemia T-cells of CEM T4 and Jurkat lines were shown to be sensitive to toxic effect of the lectin and another protein toxovirin isolated from A. virosa fruit bodies It was found that toxovirin possessed an enzymatic activity of l-amino acid oxidase. Since both toxic proteins - the lectin and toxovirin - are sensitive to an elevated temperature, it is suggested that they play a significant role in human poisoning only when the unbaked mushroom is eaten.     

Isobolographic analysis of the interaction between fenoldopam and levodopa on arterial blood pressure of the rat

Fenoldopam (FD) and levodopa (LD) injected intravenously in rats in a noncumulative schedule induced dose-dependent reductions in mean arterial blood pressure. The doses that induced a 50% reduction in the initial control mean arterial pressure (referred as ED50) were calculated by linear regression analysis of the corresponding parallel dose-response curves and were 0.88 and 0.068 mg/kg, respectively. The interaction between the effects of FD and LD on pressure reduction was evaluated by simultaneous administration of different fixed ratios of FD and LD (16:1) and obtaining a dose-response curve. An isobolographic analysis was then performed, which showed that the experimental point for the effect of the simultaneous administration of FD and LD was significantly different from the theoretically calculated additive point, denoting supradditivity. It was concluded that the effect of the combination of FD and LD on mean blood pressure reduction was synergic and was probably due to an activation of D1 vascular receptors by both drugs, in conjunction with an activation of beta2 adrenoceptors by LD and a blocking action of FD on postsynaptic alpha1-adrenoceptors.