Clonorchis sinensis: molecular cloning and characterization of 28-kDa glutathione S-transferase

A 28-kDa glutathione S-transferase (Cs28GST) was purified from a Clonorchis sinensis cytosolic fraction through anion-exchange and glutathione-affinity column chromatographies. A monoclonal antibody raised against Cs28GST reacted specifically to the C. sinensis antigen among trematode proteins. A putative peptide of 212 amino residues deduced from a cDNA clone appeared homologous with 28-kDa GST of trematodes, and its secondary structural elements predicted a GSH-binding site. Recombinant Cs28GST showed GST enzyme activity with CDNB substrate and was sensitive to the model inhibitors. The recombinant Cs28GST was antigenically indistinguishable from the native form and was recognized specifically by C. sinensis-infected human sera. The Cs28GST was localized in the tegument and underlying mesenchymal tissues. It is suggested that Cs28GST may play significant physiological roles against bioreactive molecules and be a useful reagent for serodiagnosis of clonorchiasis.

Molecular cloning and characterization of an antigenic protein with a repeating region from Clonorchis sinensis

In the course of immunoscreening of Clonorchis sinensis cDNA library, a cDNA CsRP12 containing a tandem repeat was isolated. The cDNA CsRP12 encodes two putative peptides of open reading frames (ORFs) 1 and 2 (CsRP12-1 and -2). The repetitive region is composed of 15 repeats of 10 amino acids. Of the two putative peptides, CsRP12-1 was proline-rich and found to have homologues in several organisms. Recombinant proteins of the putative peptides were bacterially produced and purified by an affinity chromatography. Recombinant CsRP12-1 protein was recognized by sera of clonorchiasis patients and experimental rabbits, but recombinant CsRP12-2 was not. One of the putative peptide, CsRP12-1, is designated CsPRA, proline-rich antigen of C. sinensis. Both the C-termini of CsRP12-1 and -2 were bacterially produced and analysed to show no antigenicity. Recombinant CsPRA protein showed high sensitivity and specificity. In experimental rabbits, IgG antibodies to CsPRA was produced between 4 and 8 weeks after the infection and decreased thereafter over one year. These results indicate that CsPRA is equivalent to a natural protein and a useful antigenic protein for serodiagnosis of human clonorchiasis.

Trends in HIV seroprevalence and needle sharing among Puerto Rican drug injectors in Puerto Rico and New York: 1992-1999

This study assessed trends in HIV seroprevalence and needle-sharing behaviors among Puerto Rican injection drug users (IDUs) in Puerto Rico and New York. Data from two studies of IDUs conducted from 1992 through 1995 and 1998 through 1999 in Bayamón, Puerto Rico, and East Harlem, New York, were examined to assess trends over this period. Separate analyses were conducted for IDUs who were current crack smokers. Significant decreasing trends in seroprevalence were found among IDUs in the New York and Puerto Rico samples (p <.001). Significant decreasing trends in receptive and distributive needle sharing were found in the New York sample, and a significant decline in receptive sharing was found in the Puerto Rico sample. Overall, higher levels of needle-sharing behaviors were reported in Puerto Rico compared with New York. Decreasing trends in needle sharing and seroprevalence in both communities are an encouraging finding. Ongoing epidemiologic studies to monitor the epidemic and continued prevention efforts to help maintain or further these declines are needed, particularly to address the higher rates of needle sharing in Puerto Rico.

Cyclosporine impairs the guanylyl cyclase activity of the natriuretic peptide receptor in the glomerulus

In order to elucidate the involvement of the atrial natriuretic peptide (ANP) and its receptor (natriuretic peptide receptor; NPR) system in cyclosporine-induced nephrotoxicity, we investigated the cyclosporine A (CsA)-induced changes in characteristics of the NPR/guanylyl cyclase system in the glomerulus and inner medulla of the rat kidney. CsA was administered intramuscularly to rats for 2 weeks (CsA group). Particulate guanylyl cyclase activity was measured in glomerular and inner medullary membranes. For receptor characteristics, quantitative in vitro receptor autoradiography was performed. The guanylyl cyclase activity in the glomerulus from the CsA group was attenuated compared with that from the control. However, the activity in the inner medulla was not affected by CsA treatment. Direct application of CsA to normal glomerular membrane completely abolished the ANP-induced guanylyl cyclase activation. Binding studies, using(125)I-ANP, revealed that B(max)was decreased in the CsA group, while K(d)was not affected in the glomerulus. However, in the inner medulla, neither B(max)nor K(d)was affected by CsA treatment. CsA did not displace the(125)I-ANP bindings to NPRs in the normal rat kidney. Local tissue ANP as well as plasma ANP concentration in both groups was not significantly different. These results indicate that CsA impairs the guanylyl cyclase activity mainly in the glomerulus by the decrease in NPR population and/or by direct inhibition, suggesting that the ANP/NPR system might be involved in CsA-induced nephrotoxicity.

A vascularized osteocutaneous fibular free flap for reconstruction of a complex injury of the foot

The foot plays a vital role in standing and gait. Its function results from harmonious interaction of bones, joints, and soft tissue. An imbalance or a defect in these structures can result in problems. The cuneiform bone of the foot consists of three bones: medial, intermediate, and lateral. Its structure plays an important role in maintaining the skeletal arch and it supports the body's weight. A defect or dislocation can disrupt the distribution of the weight-bearing complex of the foot and can lead to difficult gait.

Structural and immunological characteristics of a 28-kilodalton cruzipain-like cysteine protease of Paragonimus westermani expressed in the definitive host stage

A complete cDNA sequence encoding a 28-kDa cruzipain-like cysteine protease of adult Paragonimus westermani, termed Pw28CCP, was isolated from an adult cDNA library. The cDNA contained a single open reading frame of 975 bp encoding 325 amino acids, which exhibited the structural motif and domain organization characteristic of cysteine proteases of non-cathepsin Bs including a hydrophobic signal sequence, an ERFNIN motif, and essential cysteine residues as well as active sites in the mature catalytic region. Analysis of its phylogenetic position revealed that this novel enzyme belonged to the cruzipain-like cysteine proteases. The sequence of the first 13 amino acids predicted from the mature domain of Pw28CCP was in accord with that determined from the native 28-kDa enzyme purified from the adult worm. Expression of Pw28CCP was observed specifically in juvenile and adult worms, with a location in the intestinal epithelium, suggesting that this enzyme could be secreted and involved in nutrient uptake and immune modulation. The recombinant protein expressed in Escherichia coli was used to assess antigenicity by immunoblotting with sera from patients with active paragonimiasis and from those with other parasitic infections. The resulting sensitivity of 86.2% (56 of 65 samples) and specificity of 98% (147 of 150 samples) suggest its potential as an antigen for use in immunodiagnosis.

Molecular evidence of natural hybridization between Fasciola hepatica and F. gigantica

Nucleotide sequences of two regions, cytochrome c-oxidase subunit 1 (CO1) and NADH dehydrogenase subunit 1 (ND1) of the mitochondrial DNA and two regions, internal-transcribed spacer 2 (ITS2) and the D2 region in the 28S rDNA (28S) of the nuclear DNA were obtained from five Korean worms of the genus Fasciola in order to elucidate their taxonomic status. The CO1 and ND1 regions are all monomorphic in the Korean worms and similar to those of F. gigantica. On the other hand, the ITS2 and D2 regions were found to be polymorphic; that is, out of five worms, two possessed a F. gigantica-type sequence, one, a F. hepatica-type sequence and two possessed sequences of both types indicating an existence of different alleles at the loci. It should be noted that these variations of the ITS2 and D2 regions co-occur at the same individual worms. This was confirmed by sequencing five to six cloned PCR products for each worm. The present study strongly suggests interspecific cross-hybridization between the two species coexisting in Korea.

Differential expression of the 27 kDa cathepsin L-like cysteine protease in developmental stages of Spirometra erinacei

The 27 kDa cathepsin L-like cysteine protease of Spirometra erinacei plerocercoid is known to play an important function in tissue penetration, nutrient uptake and immune modulation in human sparganosis. In the present study, the expression of this enzyme was examined at different developmental stages of S. erinacei including immature egg, coracidium, plerocercoid in tadpole and rat, and adult. Proteolytic activity against carboxybenzoyl-phenylalanyl-arginyl-7-amino-4-methylcoumarin was detected in the extracts of coracidia and plerocercoid while no activity was observed in those of immature egg and adult. The specific activity in coracidial extracts was lower than that in the plerocercoid. Reverse transcription-polymerase chain reaction and Northern blot analysis demonstrated that the gene was expressed in the coracidium and plerocercoid but not in immature egg and adult. These results suggest that the 27 kDa cysteine protease is only expressed in the stages involving active migration of the parasite in the host tissue.

Antioxidant lignans from Machilus thunbergii protect CCl4-injured primary cultures of rat hepatocytes

Eleven lignans (1-11) were isolated from the CH2Cl2 fraction of the bark of Machilus thunbergii Sieb. et Zucc. (Lauraceae). These were identified as (-)-acuminatin (1), (-)-isoguaiacin (2), meso-dihydroguaiaretic acid (3), (+)-galbacin (4), (-)-sesamin (5), (+)-galbelgin (6), machilin A (7), machilin G (8), licarin A (9), and nectandrin A (10) and B (11). Primary cultures of rat hepatocytes were co-incubated for 90 min with the hepatotoxin CCl4 and each of the 11 lignans (50 microM). Hepatoprotective activity was determined by measuring the level of glutamic pyruvic transaminase released into the medium from the primary cultures of rat hepatocytes. (-)-Acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid all significantly reduced the level of glutamic pyruvic transaminase released. Further investigation revealed that these three compounds significantly preserved the levels and the activities of glutathione, superoxide dismutase, glutathione peroxidase and catalase. (-)-Acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid also ameliorated lipid peroxidation as demonstrated by a reduction of malondialdehyde production. These results suggest that (-)-acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid exert diverse hepatoprotective activities, perhaps by serving as potent antioxidants.

A case of chronic cerebral paragonimiasis westermani

We report a chronic cerebral paragonimiasis from a 41-year-old Korean man who complains a headache and weakness of left motor neuron components. Magnetic resonance images of the brain revealed conglomerates of multiple ring-like enhancements in temporo-occipital and frontal lobes of the right hemisphere. An intradermal test for paragonimiasis westermani was positive. The patient was born near an endemic area of paragonimiasis and used to eat boiled or grilled freshwater crayfish in his childhood. Nodules in the brain were resected through craniotomies. The eggs of P. westermani were identified pathologically and parasitologically in the calcified necrotic lesions. Examinations on sputum and fecal specimens for the eggs of P. westermani were shown to be negative and a chest radiograph was normal. It is presumed that the brain lesions were formed by P. westermani approximately 30 years ago.

Dual effects of dextromethorphan on cocaine-induced conditioned place preference in mice

Dextromethorphan (DM) at supra-antitussive doses might produce psychotomimetic effects in humans. In order to understand the underlying mechanisms responsible for the behavior induced by DM, we examined the effects of DM on cocaine-induced conditioned place preference (CPP) and locomotor pattern in mice, and Fos-related antigen immunoreactivity (FRA-IR) in the striatal complex (nucleus accumbens and striatum) of the mouse brain. The effects of DM (20 and 40 mg/kg, i.p.) on the CPP for 2.5, 5, 10, and 20 mg cocaine/kg, i.p. were assessed. Pretreatment with DM dose-dependently decreased the CPP for 20 mg cocaine/kg. Similarly, pretreatment with DM appeared to reduce the CPP for 10 mg cocaine/kg, but increase the CPP for 5 mg cocaine/kg. This finding was more pronounced for 2.5 mg cocaine/kg; DM significantly increased the CPP for 2.5 mg cocaine/kg in a dose-related manner. Furthermore, these results were correlated with alterations in the locomotor pattern (marginal activity) and FRA-IR in the striatal complex. Thus, our results suggest that DM exhibits a biphasic effect on the cocaine-induced CPP and locomotor pattern.

Bleeding and subsequent anemia: a precipitant for cerebral infarction

BACKGROUND AND OBJECTIVES

The relationship between bleeding and subsequent anemia (BSA) and the occurrence of stroke has not been sufficiently studied. The purpose of the present study was to elucidate the characteristics of stroke associated with BSA.

METHODS

We studied 16 consecutive patients with acute stroke associated with anemia (hemoglobin level on admission < or =9.0 g/dl) and compared their stroke subtypes with those of 32 control subjects.

RESULTS

The cause of anemia was upper gastrointestinal bleeding in 11 patients (ulcers in 8; carcinomas in 2, and hemorrhagic gastritis in 1), bleeding from a hemorrhoid in 2, uterine cervical bleeding in 1, ecchymosis probably related to medication in 1, and chronic blood drainage in 1. At least 10 patients had a history of recent (<1 week), active bleeding. Clinical and imaging studies showed that all the patients had infarcts and none had intracerebral hemorrhages. Thirteen patients had infarcts in the region of the middle cerebral artery (MCA) (total MCA region in 2; partial, cortical area in 5; subcortical area in 5, and lenticulostriate artery region in 1), 2 had anterior cerebral artery (ACA) region infarction, and 1 had cerebellar infarction. All 11 patients who underwent vascular imaging studies showed significant stenosis and/or occlusion of the internal carotid artery (ICA) (n = 5), the MCA (n = 4), both the ICA and MCA (n = 1), or the ACA (n = 1). Of the different stroke subtypes (large vessel infarction (LVI), small vessel infarction, cardiogenic embolic infarction, intracerebral hemorrhage), LVI was significantly (p<0.05) more frequent in patients with stroke associated with BSA than in the controls, even though the demographics and risk factors were similar in each group.

CONCLUSIONS

The close temporal relationship between the bleeding and the onset of stroke, as well as the predominance of the LVI subtype in the BSA-associated group as compared to controls, suggest that BSA may precipitate atherothrombotic cerebral infarction. A hemodynamic alteration, enhanced thrombosis or a combination of these appears to be the pathogenic mechanism.

Persisting antibody reaction in paragonimiasis after praziquantel treatment is elicited mainly by egg antigens

Antibody responses in serum and cerebrospinal fluid (CSF) samples from patients with active and chronic paragonimiasis and in sera from patients on whom follow-up studies were done after praziquantel treatment were analyzed using antigens of Paragonimus westermani prepared from eggs, metacercariae, juveniles of 4- and 7-week old, adult worms and recombinant protein of 28 kDa cruzipain-like cysteine protease (rPw28CCP). The patient sera/CSFs of active and chronic paragonimiasis revealed strong antibody reactions against the crude extracts of 4- and 7-week old juveniles as well as against those from egg and adult. rPw28CCP also showed specific reaction to the sera with active paragonimiasis. After the treatment, levels of specific antibodies in the sera gradually decreased to negative range in most patients. In some cases with persisting high antibody levels, however, the reactions at 27 kDa egg protein were sustained throughout the observation period of 34 months. The reactions at 35 and 32 kDa in adult extract and rPw28CCP disappeared rapidly after the treatment. Persistent antibody reactions even after successful treatment are provoked by continuous antigenic challenge from eggs which were not resolved by treatment.

Localization of receptors for natriuretic peptide and endothelin in the duct of the epididymis of the freshwater turtle

The presence of receptor subtypes for natriuretic peptides (NPs) and endothelin (ET) in the epididymis of the freshwater turtle, Amyda japonica, was examined by quantitative in vitro autoradiography using iodinated mammalian-type atrial NP ((125)I-ANP((1-28))), phylogenically conserved C-type NP ((125)I-[Tyr(0)]-CNP((1-22))), and ET-1 ((125)I-ET-1) as radiolabeled ligands. To characterize NP receptor (NPR) subtypes, we also performed an activation of particulate guanylyl cyclase (GC) in membranes of the epididymis by NPs. Specific (125)I-ANP((1-28)) and (125)I-[Tyr(0)]-CNP((1-22)) bindings were localized in surrounding smooth muscle cell layer of the duct of the epididymis with an apparent dissociation constant (K(d)) of 0.84+/-0.15 and 1.74+/-0.39 nM and a maximal binding capacity (B(max)) of 0.47+/-0.11 and 0.08+/-0.01 fmol/mm(2), respectively. Bindings of (125)I-ANP((1-28)) and (125)I-[Tyr(0)]-CNP((1-22)) to these sites were also displaced by des[Gln(18),Ser(19),Gly(20), Leu(21),Gly(22)]ANF((4-23)), a specific ligand of the NP clearance receptor. Production of 3',5'-cyclic guanosine monophosphate by particulate GC in membranes of the epididymis was stimulated by ANP((1-28)), BNP((1-26)), and CNP((1-22)). Receptor subtypes for ET in the epididymis were characterized by competition with BQ 123 and BQ 788 as specific antagonists for ET receptors, type A (ET(A)) and type B (ET(B)) subtypes, respectively. Specific (125)I-ET-1 bindings were localized in the smooth muscle cell layer of the duct of the epididymis with K(d) and B(max) of 0.21+/-0.03 nM and 0.52+/-0.05 fmol/mm(2), respectively. These specific bindings were potently inhibited in a dose-dependent manner by BQ 123, whereas BQ 788 (10 microM) was not in competing for specific (125)I-ET-1 bindings in this structure. Therefore, these results indicate that specific NP and ET receptors are localized in surrounding smooth muscle cells of the duct of the epididymis of the freshwater turtle. It is also suggested that biological and clearance NPR-like subtypes coexist in these cells, and the predominant ET receptor subtype in this tissue is the ET(A)-like receptor. The localization of specific receptors for NPs and ET in the epididymis may be involved in the control of the transport of sperm in the freshwater turtle.

Paragonimus westermani: a cytosolic glutathione S-transferase of a sigma-class in adult stage

We purified cytosolic glutathione S-transferase (GST) of adult Paragonimus westermani monitoring its activity with 1-chloro-2,4-dinitrobenzene (CDNB). The enzyme was purified 18.4-fold to electrophoretic homogeneity with 21% recovery rate through a three-step procedure. The purified enzyme (Pw28GST) has a subunit molecular weight of 28 kDa with an isoelectric point at 4.6. Monoclonal antibody (anti-Pw28GST) against Pw28GST did not cross-react with GSTs from other helminths. cDNA library was constructed in lambdaZAP II bacteriophage and screened with anti-Pw28GST. The corresponding gene containing a single open reading frame of 804 bp encoded 211 amino acids. The predicted amino acid sequence exhibited a higher homology with catalytic domain near N-terminus of class sigma GSTs (58%) than with schistosome 28-kDa GSTs (45-41%) or with class sigma GSTs themselves (33-31%). The sequence contained both Tyr-6 and Tyr-10 that are highly conserved in mammalian and helminth GSTs. The apparent K(m) value of a recombinant enzyme was 0.78 mM. Both native and recombinant enzymes showed the highest activity against CDNB, relatively weak activity against ethacrynic acid and reactive carbonyls, and no activity against epoxy-3-(p-nitrophenoxy)-propane. The activities were inhibited by bromosulfophthalein, cibacron blue, and albendazole, but not by praziquantel. These findings indicate that adult P. westermani has a class sigma GST.

A recombinant 10-kDa protein of Taenia solium metacestodes specific to active neurocysticercosis

Neurocysticercosis (NCC) is an important cause of neurological disease worldwide. A 10-kDa antigen of Taenia solium metacestodes (TsMs) has been shown to be specific for immunodiagnosis of NCC. Screening of a TsM complementary DNA (cDNA) library isolated a cDNA encoding this protein. The cloned cDNA contained a 258-bp complete open-reading frame that encodes an 86-amino acid polypeptide with a calculated molecular weight of 9582 Da. It showed 73% homology with a 10-kDa antigen of T. crassiceps. The recombinant protein was expressed bacterially as a fusion protein at a high level. In immunoblot with recombinant protein, 97% (184/190) of sera from patients with active NCC showed strong reactivity, whereas 14% (4/29) of those from patients with chronic calcified NCC reacted weakly. In 180 sera from other patients with parasitic infections and from normal controls, it showed 98% specificity. A single recombinant TsM antigen has a high potential for serological differentiation of active NCC.

Modulation of chemical carcinogen-induced unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) in the primary rat hepatocytes

Modulation of unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) after exposure to various chemical carcinogens was investigated in the primary rat hepatocytes. Unscheduled DNA synthesis was induced by treatment of such direct acting carcinogens as methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) or procarcinogens including benzo(a)pyrene (BaP) and 7,12-dimethylbenz(a)anthracene (DMBA). Unscheduled DNA synthesis was determined by measuring [methyl-3H]thymidine radioactivity incorporated into nuclear DNA of hepatocytes treated with carcinogens in the presence or absence of DHEA. Hydroxyurea (5x10(-3) M) was added to growth medium to selectively suppress normal replication. DHEA at concentrations ranging from 1x10(-6) M to 5x10(-4) M did not significantly inhibit unscheduled DNA synthesis induced by either MMS (1x10(-4) M) or EMS (1x10(-2) M). In contrast, DHEA significantly inhibited unscheduled DNA synthesis induced by BaP (6.5x10(-5) M) and DMBA (2x10(-5) M). DHEA-induced hepatotoxicity in rats was examined using lactate dehydrogenase (LDH) release as an indicator of cytotoxicity. DHEA exhibit no significant increase in LDH release compared with the solvent control at 18 h. These data suggest that nontoxic concentration of DHEA does not affect the DNA excision repair process, but it probably influence the enzymatic system responsible for the metabolic activation of procarcinogens and thereby decreases the amount of the effective DNA adducts formed by the ultimate reactive carcinogenic species.

Effectiveness of comprehensive services for crack-dependent mothers with newborns and young children

This article presents an outcome study of the Family Rehabilitation Program (FRP), a unique network of community-based programs in New York City that provides comprehensive services to families with drug-dependent parents, most caring for prenatally cocaine-exposed newborns. An admission sample of 173 mothers in 17 FRP sites was studied for one year; substance use was assessed by hair analysis and self-report. Mean length of retention was 10 months; half the clients were still active in the program at follow-up. Mothers completing or still active in FRP had higher rates of abstinence and substantially lower average levels of cocaine in their hair at follow-up than those exiting prematurely. The percent of families with children out of their homes did not increase significantly between admission and follow-up, and completing or remaining active in the program were associated with less out-of-home placement at follow-up.

Pancreatic exocrine-endocrine interrelationship. Clinical implications

The exocrine and endocrine pancreata are anatomically and functionally interrelated. As a result, exocrine pancreatic dysfunction often accompanies endocrine pancreatic dysfunction and vice versa. This article delineates the nature of these exocrine and endocrine pancreatic interrelationships and their clinical significance in the management of pancreatic disorders.

Program quality effects on patient outcomes during methadone maintenance: a study of 17 clinics

This study was designed to replicate Ball and Ross's benchmark research, which was the first to identify a set of program quality factors for methadone maintenance programs and relate them to patient outcomes. Ball and Ross's treatment domain variables were measured in a new and larger sample of methadone clinics, and eight candidate program quality factors were derived. Both studies found that program factors defined by more frequent counseling contacts, higher director involvement with treatment, and more director experience were associated with lower drug use by patients during treatment. Several patient and counselor characteristics also were associated with drug-use outcomes.

Alpha2-adrenoceptor antagonists evoke endothelium-dependent and -independent relaxations in the isolated rat aorta

This study was designed to determine whether the alpha2-adrenoceptor antagonists idazoxan, yohimbine, and rauwolscine cause endothelium-dependent and -independent responses in the rat aorta. Rings of rat aorta, with and without endothelium, were suspended for the measurement of isometric force in modified Krebs-Ringer bicarbonate solution (37 degrees C; aerated with 95% O2 and 5% CO2). The alpha2-adrenoceptor antagonists, in the concentration range of 10(-8)-10(-6) M, relaxed phenylephrine-contracted rings with, but not those without endothelium. alpha2-Adrenoceptor antagonists (3 x 10(-6) M for 1 min) increased the accumulation of cyclic guanosine monophosphate (cGMP) about twofold in the aortas with endothelium. The relaxation and the increased cGMP induced by alpha2-antagonists were attenuated by methylene blue (10(-6) M) and N(G)-nitro-L-arginine (L-NA, 3 x 10(-5) M), whereas propranolol (10(-6) M) did not affect the relaxation. In concentrations >10(-6) M, alpha2-adrenoceptor antagonists relaxed the rat aorta without endothelium. The endothelium-independent relaxation by alpha2-adrenoceptor antagonists was abolished by increased external K+ and reduced significantly by tetraethylammonium (TEA, 10(-2) M, a Ca2+-dependent K+ channel blocker), but not inhibited by glibenclamide (10(-5) M, an ATP-sensitive K+ channel blocker). In the rabbit aorta, only endothelium-independent relaxations were observed with alpha2-adrenoceptor antagonists in the concentration range of 10(-8)-10(-5) M, and these relaxations were not antagonized by TEA. These results suggest that alpha2-adrenoceptor antagonists relax the rat aorta through endothelium-dependent mechanism at lower concentrations and endothelium-independent mechanisms at higher concentrations. The endothelium-dependent relaxations are likely to be mediated by the endothelium-derived relaxing factor (EDRF)/NO pathway because they are associated with the accumulation of cGMP, whereas the endothelium-independent relaxations may be caused by the opening of potassium channels in the vascular smooth muscle.