Occurrence of fumonisins and aflatoxins in corn from Thailand

Eighteen corn samples collected from Thailand were analysed for fumonisins and aflatoxins by high performance liquid chromatography. Fumonisins B1 and B2 were detected in 16 (89%) and 12 (67%) samples at levels ranging from 63 to 18800 ng/g (mean, 1790 ng/g) and from 50 to 1400 ng/g (mean, 251 ng/g), respectively. Fusarium moniliforme and F. proliferatum isolated from Thai corn showed the production of fumonisins in corn grit cultures. Aflatoxins B1 and B2 were found in 15 and 10 samples at mean levels of 72 and 15 ng/g, respectively. It was noted that as many as 72.2% (13/18) of samples were coincidentally contaminated with fumonisins and aflatoxins. Based on these results, the interaction of fumonisin-producers and aflatoxin-producers on kernel infection and contamination of these mycotoxins in corn is discussed. This is the first report on the natural co-occurrence of fumonisins and aflatoxins in Thailand.

Role of yolk sac endodermal cells with special reference to the fetal macrophage differentiation

The morphological and functional characteristics of rat yolk sac endodermal cells, with particular reference to fetal macrophage (M phi) differentiation, were studied in vivo and in vitro using DA rat embryos from 8 to 16 days of gestation. At a very early stage (day 5-6) of gestation, endodermal cells are derived from proximal endoderm as an essential and multipotent organ with various primitive functions. Based on toluidine blue staining properties and ultrastructures, we demonstrated that the endodermal cell layer of 8-16-day yolk sacs consists of two cell types, "clear" cells with clear cytoplasm (10%) and "dark" cells with dark cytoplasm (90%), and hypothesized that the endodermal cell layer is heterogeneous at both the morphological and functional levels. We produced three different monoclonal antibodies (mAbs), designated Mar 1, Mar 2, and Mar 3, that recognize rat M phi populations. Mar 1 binds specifically to the cells constituting the mononuclear phagocyte system (MPS). M phi Mar 3 antigen is a phagocytosis-associated molecule, and Mar 2 antigen is a differentiation antigen of the M phi subset. Application of these mAbs in both in vivo and in vitro studies allowed the functional capability and differentiation of fetal M phis to be assessed. The Mar 3 antigen was expressed first on proximal endodermal cells on day 6 yolk sac and continued to be presented afterward. In vitro culture study demonstrated that the adhesive, phagocytic Mar 3+-Mar1+ M phis differentiate from M phi precursors in the endodermal cell layer after the first 13 days of gestation. Based on these findings, we proposed that clear cells in the endodermal cell layer are derived from precursor dark cells, detach from the layer, move to the mesenchymal stromas, and subsequently migrate to the fetal liver, loose connective tissue, and other intraembryonic tissues, and consequently they differentiate free Mar 1+ M phis during gestation (day 13-15). Thus, the M phi differentiation and the peripherization of the M phis could be almost fully developed during the prenatal period.

Enzymatic synthesis of anandamide, an endogenous cannabinoid receptor ligand, through N-acylphosphatidylethanolamine pathway in testis: involvement of Ca(2+)-dependent transacylase and phosphodiesterase activities

Rat testis was shown to contain significant amounts of both N-acylethanolamine, including N-arachidonoylethanolamine (anandamide), and N-acylphosphatidylethanolamine (N-acylPE), including N-arachidonoylPE. The fatty acid profiles of the N-acyl moieties of the two classes resembled each other. We confirmed that testis microsomes contain a phosphodiesterase activity catalyzing the release of anandamide from N-arachidonoylPE. They also contain an enzyme activity catalyzing the transfer of arachidonic acid from the 1-position of diacylphospholipids to PE to form N-arachidonoylPE. These results suggest that the N-acylPE pathway is important in the synthesis of anandamide in this tissue.

Effects of the mycelial extract of cultured Cordyceps sinensis on in vivo hepatic energy metabolism in the mouse

Mice were given the extract of cultured Cordyceps sinensis (Cs) (200 mg/kg daily, p.o.) for 3 weeks. In vivo phosphorus-31 nuclear magnetic resonance (NMR) spectra of the liver were acquired at weekly intervals using a surface coil. From 1 to 3 weeks, a consistent increase in the ATP/inorganic phosphate ratio, which represents the high energy state, was observed in the Cs extract-treated mice. The intracellular pH of the Cs extract-treated mice was not significantly different from that of the control mice. No steatosis, necrosis, inflammation or fibrosis were observed in the liver specimens from Cs extract-treated mice.

Protective effect of KBT-3022, a new cyclooxygenase inhibitor, in cerebral hypoxia and ischemia

The protective effect of KBT-3022 (ethyl 2-[4,5-bis-(4-methoxyphenyl)thiazol-2-yl]pyrrol-1-ylacetate) , a new cyclooxygenase inhibitor, in cerebral hypoxia and ischemia was studied and compared with those of indomethacin and acetylsalicylic acid (ASA). Oral administration of KBT-3022 (3-100 mg/kg) and indomethacin (3 and 10 mg/kg) significantly prevented KCN-induced death in mice, while ASA (100 mg/kg) had no effect. KBT-3022 (3 and 10 mg/kg, p.o.) and indomethacin (10 mg/kg, p.o.) significantly prolonged the survival time of mice subjected to normobaric hypoxia, while ASA (100 mg/kg, p.o.) had no effect. KBT-3022 (3-30 mg/kg, p.o.) and indomethacin (3 mg/kg, i.p.) significantly ameliorated delayed neuronal death in the gerbil hippocampal CA1 sector after occlusion of bilateral carotid arteries for 5 min, while ASA (300 mg/kg, p.o.) had no effect. KBT-3022 (10 mg/kg, p.o.) significantly inhibited ATP depletion in the gerbil hippocampus after a 1-min occlusion of bilateral carotid arteries, but had no effect on ATP depletion after a 5-min occlusion and the recovery during recirculation. These results show that KBT-3022 exerts protective effects against cerebral anoxia and hypoxia and ameliorates delayed neuronal death in the hippocampus. KBT-3022 may therefore be useful for prophylaxis of ischemic cerebrovascular disorders.

Acyl-CoA binding and acylation of UDP-glucuronosyltransferase isoforms of rat liver: their effect on enzyme activity

When [14C]arachidonoyl-CoA was incubated with crude extracts of rat liver microsomes, [14C]arachidonic acid was incorporated into many proteins, suggesting that modification of these proteins with fatty acid, i.e. acylation, occurred. Using a [14C]arachidonyl-CoA labelling assay, 50 and 53 kDa proteins were purified from rat liver microsomes to near homogeneity by sequential chromatography on Red-Toyopearl, hydroxyapatite, heparin-Toyopearl, Blue-Toyopearl and UDP-hexanolamine-agarose. Acylation of the 50 and 53 kDa proteins occurred in the absence of any other protein, suggesting that these molecules catalyse autoacylation. The acylation was dependent on the length of the incubation period and the concentration of [14C]arachidonoyl-CoA. The 50 and 53 kDa proteins also had acyl-CoA-binding activity; initial rates of acyl-CoA binding and acylation were 0.25 and 0.004 min-1 respectively. The proteins also had weak but distinct acyl-CoA-hydrolysing activity (0.006 min-1). These results suggest that the proteins catalysed the sequential reactions of binding to acyl-CoA, autoacylation, and hydrolysis of fatty acid. N-terminal amino acid sequencing analysis showed these proteins to be UDP-glucuronosyltransferase (UDPGT) isoforms. UDPGT activity was inhibited by arachidonoyl-CoA. These results suggest that binding of acyl-CoA and acylation of UDPGT isoforms regulate the enzyme activities, implying a possible novel function for fatty acyl-CoA in glucuronidation, which is involved in the metabolism of drugs, steroids and bilirubin.

2-Arachidonoylglycerol: a possible endogenous cannabinoid receptor ligand in brain

The effects of anadamide, 2-arachidonoylglycerol and related compounds on the specific binding of a radiolabeled cannabinoid receptor ligand,[3H]CP55940, to synaptosomal membranes were examined. Anandamide, an endogenous cannabinoid receptor ligand, reduced the specific binding of [3H]CP55940 to synaptosomal membranes in a dose-dependent manner: the Ki value was 89 nM. 2-Arachidonoylglycerol was also shown to bind appreciably to the cannabinoid receptor in competitive inhibition experiments. The apparent binding affinity was markedly increased when the binding assay was carried out in the presence of the esterase inhibitor DFP or at 0 degrees C. Free arachidonic acid and N-palmitoylethanolamine were almost inactive in terms of binding to the cannabinoid receptor in synaptosomal membranes. 2-Arachidonoylglycerol may be an endogenous cannabinoid receptor ligand in the brain.

[Asymptomatic unilateral adrenal medullary hyperplasia with a cyst: case report]

A 45-year-old man was admitted with asymptomatic adrenal tumor. He had normal plasma and urinary catecholamine levels. The swelling of right gland was detected by CT scan and MRI. Selective venous samplings were performed and the level of catecholamine into the right adrenal vein were much higher than that into the left one. On July 15th, 1993, a right adrenalectomy was carried out and the right adrenal gland with a large cyst could be found. The ratio of cortical area to medullary area was about 4:1. Therefore, it was pathologically diagnosed as adrenal medullary hyperplasia with a cyst. There are relatively few reports of adrenal medullary hyperplasia. Before the operation, the patients were mostly diagnosed as pheochromocytoma by the results of laboratory studies and their symptoms. The condition of this disease is usually bilateral and often associated with type II multiple endocrine neoplasia (MEN II). We describe a case of asymptomatic unilateral adrenal medullary hyperplasia.

[Renal angiomyolipoma: diagnosis and treatment]

In 10 years the diagnosis of renal angiomyolipoma (RAML) was made in 14 patients (male-to female ratio 1:3.7) at our institution; 1 case was associated with tuberous sclerosis (TS) and 1 case had regional lymph node involvement. A statistical study was done on data taken from 739 cases of RAML in the Japanese literature, including our cases. The male to female ratio was 1 to 3. Twenty eight percent of the cases were associated with TS. The ratio of bilateral cases to the unilateral one was 1 to 3. The main clinical signs were flank pain, abdominal mass, hematuria and fever elevation. Recently the ratio of nephrectomy has decreased to 30%. The percentage of detecting the fat component by ultrasonography (US), computed tomography (CT) and magnetic resonance imaging were 88.1%, 86.5% and 80.8% respectively. The percentages of visualizing hypervascularity, aneurysms, absence of arterio-venous shunt and onion peel appearance by selective renal angiography were 77.3%, 71.4%, 48.1% and 4.9% respectively. Small (less than 3 cm), asymptomatic, simple lesions with adipose component may be observed annually by CT and US until more experiences is gained with surveillance of these patients. Embolization was useful for emergency cases or pre-treatment of nephron sparing surgery, but insufficient by itself. As there still remain problems in the diagnosis of RAML, especially in the case of very small tumors, in the case with almost no adipose component and in the case associated with renal cell carcinoma, the diagnosis of RAML should be made synthetically including angiography.

Effect of KBT-3022, a new diphenylthiazole derivative, on platelet functions

The effects of KBT-3022 and its metabolite desethyl KBT-3022 on platelet aggregation were determined in rat, guinea-pig, rabbit and human platelets in-vitro and ex-vivo. KBT-3022 and desethyl KBT-3022 inhibited platelet aggregation induced by arachidonic acid and collagen in-vitro more potently than aggregation induced by adenosine diphosphate, platelet-activating factor or thrombin, as well as by acetylsalicylic acid, and their effects were approximately 100 times more potent than those of acetylsalicylic acid. Desethyl KBT-3022, but not KBT-3022 or acetylsalicylic acid, inhibited thrombin-induced aggregation and 5-hydroxytryptamine release from platelets more potently than ticlopidine hydrochloride at higher concentrations. Oral administration of KBT-3022 inhibited both arachidonic acid- and collagen-induced platelet aggregation and reduced platelet retention in a glass-bead column approx. 100 times more potently than acetylsalicylic acid. KBT-3022 showed little or no anti-inflammatory effect on either ultraviolet-induced erythema or arachidonic acid induced ear oedema, and had lower gastro-ulcerogenicity than acetylsalicylic acid. These results suggest that KBT-3022 is a potent inhibitor of platelet activation with weak side-effects.

Fusarium mycotoxins (fumonisins, nivalenol, and zearalenone) and aflatoxins in corn from Southeast Asia

Corn samples collected from the Philippines, Thailand, and Indonesia were surveyed for the natural occurrence of Fusarium mycotoxins (fumonisins, trichothecenes, and zearalenone) and aflatoxins. Fumonisins B1 and B2 were found in over 50% of corn samples in individual countries, and their co-occurrences with aflatoxins at the incidence of 48% were noted. In addition to these mycotoxins, a trichothecene, nivalenol, and an estrogen, zearalenone, both mycotoxins of Fusarium species, were detected in these Southeast Asian samples. This is the first report on the simultaneous occurrence of two carcinogenic mycotoxins, fumonisins and aflatoxins, together with Fusarium mycotoxins (nivalenol and zearlenone) in corn from Asian tropics.

Platelet-activating factor and its structural analogues in the earthworm Eisenia foetida

The earthworm Eisenia foetida was shown to contain large amounts of ether-containing phospholipids such as alkylacylglycerophosphocholine (61.3% of choline glycerophospholipids) and alkenylacylglycerophosphoethanolamine (66.0% of ethanolamine glycerophospholipids). We also found a substantial amount of ether-containing PAF-like lipid in this animal, its level being increased after the animal is injured. We showed evidence that this PAF-like lipid consists of PAF and PAF analogues containing short chain fatty acids other than acetic acid. Notably, a propionic acid-containing species but not PAF itself, is the most predominant species in this animal. We also confirmed that the earthworms contain enzyme activities involved in the synthesis of PAF and short chain fatty acid-containing PAF analogues. Interestingly, the acetyltransferase activity in earthworms is resistant to high concentrations of the substrate lysophospholipid. Thus, both the structure of the PAF-like lipid and the properties of the enzymes involved in the PAF-like lipid metabolism in the earthworms are somewhat different from those in mammalian tissues.

[Composite arterial conduits with internal thoracic artery and inferior epigastric artery for a myocardial revascularization]

From November 1992 to February 1995, 10 patients were submitted to myocardial revascularization using composite arterial conduit with internal thoracic artery (ITA) and inferior epigastric artery (IEA). The age ranged from 48 to 68 years (mean age, 60.3 years); all patients were male. All patients had double-or triple vessel disease. The mean ejection fraction was 61.8% (range, 43 to 77%). We used 28 arterial conduits including 5 right ITAs, 10 left ITAs, 10 IEAs, and 3 right gastroepiploic artery. 10 IEAs were anastomosed to one ITAs and 10 composite arterial conduits were constructed (branched in 3, lengthened in 7). In 5 patients a double ITAs were used in a single patient. There was no operative mortality and fetal complication. Early postoperative angiographic controls demonstrated 100% patency of composite grafts in 9 of 10 patients. The composite arterial graft using ITAs and IEAs is feasible and the anastomoses so performed are completely safe.

Anti-thrombotic activity of KBT-3022 in experimental models of thrombosis

In this study, we investigated the effects of KBT-3022 (ethyl 2-[4,5-bis(4-methoxyphenyl)-thiazol-2-yl]pyrrol-1-ylacetate) , a potent and long-lasting anti-platelet agent, in several experimental thrombosis models and compared them with those of other anti-platelet drugs. Oral administration of KBT-3022 prevented arachidonic acid-induced death due to pulmonary embolism in mice and rabbits with respective ED50 values of 0.29 and 0.12 mg/kg. The protective effect of acetylsalicylic acid (ASA) against mortality was weaker than that of KBT-3022, and ticlopidine hydrochloride (TP) showed no such effect in these models. In a guinea pig arterio-venous shunt model, the inhibition by KBT-3022 of thrombus formation on a silk thread inserted into the shunt was dose-dependent and 300 and 30 times more potent than the inhibition obtained with ASA and indomethacin, respectively. In a model of aortic thrombosis induced by perivascular application of 20% silver nitrate solution, KBT-3022 (1 mg/kg, p.o.) inhibited thrombus formation significantly, ASA (100 mg/kg, p.o.) tended to inhibit it, and TP had no effect. However, in a stasis-induced venous thrombosis model in guinea pigs, TP inhibited thrombus formation significantly, but KBT-3022 and ASA were ineffective. These results suggest that KBT-3022 may be a useful drug for the treatment and/or prophylaxis of thrombus formation in shunts and aortic thrombosis.

[Clinical study of prostatic cancer--statistical analysis of 184 cases in the latest 21 years]

One hundred and eighty-four patients with prostatic cancer were treated at Mie University Hospital from 1973 to 1993. They were between 47 and 90 years old, with an average age of 71.8 years old. One hundred and fifty-eight patients (85.8%) were in either stage C or D. Of the 146 cases histologically examined, 17.8% were well differentiated adenocarcinoma, and 47.9% and 34.2% were moderately and poorly differentiated adenocarcinomas, respectively. The overall 3-year, 5-year and 10-year survival rate were 64.2%, 44.9% and 24.2%, respectively. The patients with high stage and/or poorly differentiated adenocarcinomas revealed worse prognosis. Although the prognosis in the patients treated with estrogen and orchiectomy was better than that with estrogen alone, there was no significant difference between the 2 treatment groups. The prognosis of patients with prostatic cancer has been improved since 1988. A possible explanation is that prostate specific antigen has been introduced as a tumor marker, which might contribute to an accurate diagnosis in prostatic cancer and improve the prognosis of the disease. In conclusion, the diagnosis in lower stage and radical prostatectomy might bring favorable prognosis. In future, safer and more effective chemotherapy and endocrine therapy including LH-RH analogue are awaited, to obtain a better prognosis in the patients with advanced prostatic cancer.

Coenzyme A-dependent cleavage of membrane phospholipids in several rat tissues: ATP-independent acyl-CoA synthesis and the generation of lysophospholipids

Substantial amounts of acyl-CoA were formed when microsomes from several rat tissues were incubated with varying concentrations of free CoA and bovine serum albumin even in the absence of ATP and Mg2+. For instance, 86 nmol of acyl-CoA was produced when microsomes (5 mg protein) were incubated with 300 microM CoA for 30 min. It was calculated that 1.8% of total fatty acyl residues were converted to acyl-CoA during the incubation. No appreciable amount of acyl-CoA was formed from free fatty acid or from boiled microsomes under the same experimental conditions. These observations indicate that acyl-CoA is formed from microsomal lipids by an enzyme activity distinct from previously known long-chain fatty acyl-CoA synthetase. The apparent Km value for CoA and Vmax were 180 microM and 20 nmol/30 min per mg protein, respectively. We found that several species of acyl-CoA such as arachidonoyl-CoA were preferentially synthesized through the reaction and that several types of phospholipids actually act as acyl donors in the formation of acyl-CoA. Phosphatidylinositol and phosphatidylcholine appear to be preferred substrates. We confirmed that lysophosphatidylinositol and lysophosphatidylcholine were generated along with the formation of acyl-CoA. It seems very likely that CoA-mediated cleavage of phospholipids/ATP-independent acyl-CoA synthesis is implicated in the metabolism of certain types of fatty acyl residues of membranous phospholipids in mammalian cells.

Coenzyme A-dependent modification of fatty acyl chains of rat liver membrane phospholipids: possible involvement of ATP-independent acyl-CoA synthesis

Certain species of fatty acyl chains of microsomal lipids from rat hepatocytes underwent desaturation when the microsomal fraction was incubated with CoA and NADH. For instance, 18:0, 18:2(n-6), and 20:3(n-6) incorporated into membrane lipids were gradually converted to 18:1(n-9), 18:3(n-6), and 20:4(n-6), respectively. Further, 20:5(n-3) and 18:3(n-6) were metabolized to 22:5(n-3) and 20:4(n-6) respectively, through chain elongation or chain elongation plus subsequent desaturation when malonyl-CoA was present. In contrast to esterified fatty acids, negligible change was observed for fre fatty acids under the same experimental conditions. It is apparent that ATP-independent acyl-CoA synthesis is implicated in such enzymatic modification of fatty acyl chains. The presence of either gel-filtered cytosol or bovine serum albumin markedly potentiated the reaction. However, the addition of ATP and Mg2+ did not accelerate the overall reaction induced in the presence of CoA alone. These results suggest that the pathway of CoA-dependent/ATP-independent modification of fatty acyl chains is sufficiently active to account for the desaturation and chain elongation of fatty acids esterified in membrane lipids, especially phospholipids, of living cells.

The effects of KBT-3022, a new anti-platelet agent, on hemorheological properties in guinea pigs

Using guinea pigs, a study was conducted on the effects of KBT-3022, a new anti-platelet agent, on hemorheological properties in various tests including blood filterability, blood viscosity, shear stress-induced red blood cell (RBC) deformability and contents of ATP and 2,3-diphosphoglycerate (2,3-DPG). Oral administration of KBT-3022 at 1 and 10 mg/kg significantly increased blood filterability, and significantly reduced blood viscosity at 10 mg/kg without changing the hematocrit, plasma fibrinogen concentration or plasma viscosity. KBT-3022 (10 mg/kg, p.o.) improved RBC deformability in response to shear stress, which was evoked by passing the blood through a thin tube. This dose of KBT-3022 also increased the contents of ATP and 2,3-DPG in RBC. These findings indicate that KBT-3022 may reduce blood viscosity as a sequel to improvement of RBC deformability through direct action on RBC. The increase in the intracellular levels of ATP and 2,3-DPG was considered to be involved in this improvement of hemorheological properties. These hemorheological effects of KBT-3022 appear to be promising for the treatment of patients with ischemic vascular disease.

[Effect of direct pulsatile peritoneal dialysis on peritoneal permeability and lymphatic absorption in the rat]

Continuous vibration of the abdominal wall with a small electric vibrator was conducted to enhance peritoneal mass transport in rats with normal kidney function. Thirty ml of either 2.5% or 4.25% dextrose dialysate containing creatinine, urea and dextran 70 was infused intraperitoneally and was allowed to dwell for 30-240 min with or without abdominal wall vibration at the rate of 80 Hz. The mass transfer area coefficient (KA) of small molecular solutes and peritoneal lymphatic absorption were investigated. Peritoneal dialysis with vibration for 60 min increased the KA of urea, creatinine and glucose by 12%, 15%, 27%, respectively, without changes in ultrafiltration and lymphatic absorption. This effect may be attributed to enhanced mixing of dialysate in the peritoneal cavity and the increased peritoneal effective blood flow. This concept can be applied to short-term dwell dialysis, such as automated peritoneal dialysis.

Cell type-specific heterogeneity of the HIV-1 V3 loop in infected individuals: selection of virus in macrophages and plasma

The primary targets for infection of HIV-1 are CD4+ T cells and monocyte/macrophage cells. We investigated the genotype heterogeneity of HIV-1 in distinct blood compartments, CD4+ T cells, monocytes, and plasma. Nucleotide sequences of proviral DNA from CD4+ T cells, monocyte cells, and cell-free virion RNA from plasma were determined in three HIV-1 infected individuals. We found that the heterogeneity in proviral DNA from CD4+ T cells was much higher than that found in monocyte cells or in virion RNA from plasma. These data showed that different swarms of HIV-1 exist in individually infected cells and plasma. Furthermore, predicted V3 amino acid sequences in the infected monocytes were very similar to the reported sequence of prototypic macrophage-tropic HIV-1 isolates. Our results show that macrophage-tropic virus is quite homogeneous in monocytes/macrophages and has a common V3 structure in contrast to T-cell-tropic virus in vivo.

Pharmacological profile of gastric mucosal protection by marmin and nobiletin from a traditional herbal medicine, Aurantii fructus immaturus

We studied the effects of marmin and nobiletin on the experimental acute gastric lesions, gastric transmucosal potential difference (PD) and gastric motor activity in rats and the contractions of isolated guinea pig ileum. Oral administration of marmin and nobiletin inhibited both the appearance of ethanol-induced gastric hemorrhagic lesions dose-dependently in a dose range of 10-50 mg/kg, with ED50 values for marmin and nobiletin being 17.2 and 8.0 mg/kg, respectively. However, marmin and nobiletin had minimal effects on aspirin-induced gastric lesions at a dose of 50 mg/kg, respectively. Marmin and nobiletin had no significant influence on the basal PD. Intragastrical administration of marmin and nobiletin at a dose of 25 mg/kg significantly prevented the PD reduction induced by ethanol. Both marmin and nobiletin given intragastrically at 25 mg/kg significantly inhibited gastric motor activity measured as intraluminal pressure recordings. Marmin and nobiletin exhibited concentration-dependent relaxations of contractions induced by acetylcholine, transmural electrical stimulation and histamine in isolated guinea pig ileum, respectively. These findings suggest that the anti-ulcer effects of marmin and nobiletin are ascribed primarily to the maintenance of the mucosal barrier integrity and inhibition of gastric motor activity and secondarily due to the prevention of the effects of endogenous acetylcholine and histamine.