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Biomedical subjects

Y Takehara

Publications and source records attributed to Y Takehara.

At least 55 records · Page 3Linked to original sources
PubMed1998

[Maximum intensity projection (MIP) and multiplanar reformation (MPR) for post-processing cholangiopancreatographic data set--clinical application and pitfalls].

Maximum intensity projection (MIP) and multiplanar reformation (MPR) are the most frequently used algorithms for MR cholangiopancreatography (MRCP). The MIP allows three dimensional overview of the pancreatic and biliary system. Because of its resemblance to ERCP images, MIP reconstruction is widely accepted by clinicians. In spite of its usefulness, MIP may be misleading without a proper reference to source images or a guidance of MPR. Opacification defects that reflect intra-ductal or intra-cystic pathologies are notably erased through the process of MIP reconstruction. Diagnosis based only on MIP images is therefore not clinically feasible. A combined use either of multisection images, or at least source images, is essential. The MPR on the other hand, enables an investigation of the details of the intra-ductal or intra-cystic pathologies. Detailing with MPR and surveying with MIP work together in interpreting MRCP data set.

Biliary Tract↗
PubMed1998

[Clinical efficacy of MRCP for diagnosis of patients with pancreatic neoplasm].

We examined the usefulness of MRCP in pancreatic cancer compared with ERCP. Moreover, it examined in the same way in focal pancreatitis, too. We compare three findings of 1) main pancreatic duct, 2) branches of the stricture part, 3) side of tail main pancreatic duct about ERCP and MRCP. As for the branches of the stricture part, MRCP was poor compared with ERCP but as for the property of the side of the tail main pancreatic duct, MRCP excelled. The study of mass forming chronic pancreatitis was a similar result and was not the one, which excels ERCP in case of qualitative diagnosis. However, we thought that it was not invasively, suitable behind the digestive operation and digestive passage fault, in case of elapse observation and moreover that MRCP is suitable for pick up the pancreatic cancer in our clinic.

Adenocarcinoma↗
PubMed1997

MR angiography of the renal artery: comparison of breath-hold two-dimensional phase-contrast cine technique with the phased-array coil and breath-hold two-dimensional time-of-flight technique with the body coil.

Breath-hold 2D phase-contrast (PC) cine MR angiography with a phased-array coil and 2D time-of-flight (TOF) MR angiography were performed in the renal arteries and their findings were compared. Breath-hold 2D thin slice PC and TOF MR angiography were performed in 10 normal volunteers for renal arteries. A PC technique with k-space segmentation was utilized with the phased-array coil. A PC technique provided visualization of the renal artery more distally than a TOF technique (4.8 +/- 0.5 cm vs. 3.7 +/- 0.8 cm). With cardiac triggering, distal renal arteries were well demonstrated in PC MR angiography. On PC images, up- or downward movements of the mid to distal renal arteries with aortic pulsatility were recognized. The quality of the images was better with the PC than with the TOF technique (3.4 vs. 2.7). The mid to distal portions of the renal arteries translationally move with aortic pulsatility. To consistently visualize and evaluate them on MR angiography, cardiac triggering might be required to reduce the effects of pulsatile motions of the renal artery in the use of a phased-array coil.

Adult↗
PubMed1997

Do reactive oxygen species underlie the mechanism of apoptosis in the tadpole tail?

Although "programmed cell death" has been postulated to underlie the mechanism for the disappearance of the tadpole tail, critical factors that trigger this phenomenon remain to be elucidated. To investigate the mechanism for the disappearance of the tail, changes in morphology, DNA status and the enzymes which metabolize reactive oxygen species were determined in the tail of Rana rugosa tadpoles. Histological examination revealed that apoptotic cell death was apparent in the tail myocytes during metamorphosis. Electrophoretic analysis of the tail DNA revealed a marked fragmentation. During the apoptotic changes, the activity of Cu/Zn-type superoxide dismutase (SOD) in the tail markedly increased with a concomitant decrease in its catalase activity. The apoptotic process was markedly enhanced by adding hydrogen peroxide (H2O2) and aminotriazole, a catalase inhibitor, to the medium. These observations suggested that apoptotic cell death in the tadpole tail might be triggered, at least in part, by a mechanism depending on active oxygen species, such as H2O2.

Amitrole↗
PubMed1997

MR angiography of aneurysm models of various shapes and neck sizes.

PURPOSE: To investigate the signal intensity of lateral and terminal saccular aneurysm models with differing neck sizes using three-dimensional time-of-flight (TOF) MR angiography with various imaging parameters. METHODS: The study included four lateral and four terminal saccular aneurysm models with pulsatile flow. The height and fundus diameter were 10 mm; the neck diameters were 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively. Each aneurysm model was examined with fast imaging with steady-state precession MR sequences with parameters of 20-140/7 (repetition time/echo time) and flip angles of 10 degrees to 30 degrees. Signal intensity was measured and compared among the models. RESULTS: Three-dimensional TOF MR angiography with the shorter repetition time and/or larger flip angle showed weaker signal intensity in the aneurysm models. Stronger signal intensity was obtained in the terminal saccular aneurysm models and/or the models with a wider neck than in the lateral saccular aneurysm models and/or the models with a narrower neck. In some aneurysm models, longer repetition times produced greater signal intensity than that of background brain models, but not in aneurysms with narrow necks. CONCLUSION: Noncontrast 3-D TOF MR angiography delineated terminal saccular aneurysms and/or aneurysms with wider necks and did not delineate lateral saccular aneurysms and/or aneurysms with narrower necks. Longer repetition times are recommended to allow the spins flowing into the aneurysms to recover.

Artifacts↗
PubMed1996

Evidence that endogenous GRP in rat stomach mediates omeprazole-induced hypergastrinemia.

To investigate the physiological role of endogenous gastrin-releasing peptide (GRP) in regulating the release of gastrin, we evaluated the response of intragastric pH, gastrin, and GRP after omeprazole treatment in rats. A significant elevation of the plasma level of GRP (P < 0.01) and a significant reduction of the antral content of GRP (P < 0.05) were observed after the administration of 100 mg/kg omeprazole. The antral content of GRP was significantly decreased 12 h after omeprazole administration and thereafter gradually returned to control levels. Peak values for intragastric pH and plasma GRP were observed 3 h after omeprazole administration and before the peak of serum gastrin. The bombesin antagonist [D-Phe6]-bombesin-(6,13)-methyl ester significantly inhibited gastrin release after omeprazole treatment (P < 0.05). These observations indicate that omeprazole-induced inhibition of acid secretion stimulates the release of GRP and suggest that the secretion of GRP induced by omeprazole may stimulate the secretion of gastrin, at least in the early phase.

Animals↗
PubMed1996

Oxygen-dependent-regulation of Ehrlich ascites tumor cell respiration by nitric oxide.

Effects of nitric oxide (NO) on oxygen uptake of Ehrlich ascites tumor cells (EATC) were examined in a study of the biological actions of NO on respiration and energy metabolism at the cellular level. Endogenous respiration of EATC was inhibited reversibly by NO in a dose dependent manner. Oxyhemoglobin, an NO trapping agent, restored the respiration promptly. The inhibitory action of NO also depended on oxygen-concentration, and the duration of suppression was prolonged remarkably at low oxygen tension. Similar inhibition was also observed in the presence of glucose. In this case, both lactate production and glucose consumption were promoted by NOC 18, an NO generating agent, and the activation was enhanced by lowering the oxygen-concentration. Furthermore, the membrane potential of EATC was depolarized transiently by adding NO, and the degree of depolarization was decreased in the presence of glucose. These results suggest that at physiologically low oxygen tension in ascites fluid, NO acts not only as a cytotoxic respiratory inhibitor but also as a regulatory factor in the energy metabolism of EATC.

Animals↗
PubMed1996

Oxygen-dependent reversible inhibition of mitochondrial respiration by nitric oxide.

Effects of nitric oxide (NO) and NO generating agents, on the electron transport system of mitochondria were examined in a study of the mechanism and physiological importance of NO in energy metabolism. In the presence of various substrates, uncoupled respiration was inhibited by NO in manner which was both dose- and oxygen tension-dependent. Simultaneously measuring changes in cytochrome absorption spectra and respiration showed that the site of action of NO is cytochrome oxidase. Similar inhibition was also brought about by 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18), an NO donor. Electron paramagnetic resonance (EPR) analysis revealed that inhibition of uncoupled respiration occurred only during the presence of NO in the reaction mixture. The inhibitory effect of NO was increased significantly by lowering the concentration of mitochondrial protein. No appreciable inhibition of respiration was observed in the presence of 3-morpholinosydnonimine (SIN-1), a peroxynitrite anion (ONOO-) generating reagent, but inhibition did occur in the presence of superoxide dismutase (SOD). These results indicate that NO reversibly interacts with mitochondria at complex IV thereby inhibiting respiration particularly under physiologically low oxygen tension and that de novo generated ONOO may have no significant effect under the present experimental conditions.

Animals↗
PubMed1996

Inhibition of neutrophil-superoxide generation by alpha-tocopherol and coenzyme Q.

Effects of various derivatives of alpha-tocopherol (VE) and coenzyme Q (CoQ) on superoxide (O2.-) generation of neutrophils and protein kinase C (PKC) activity were examined. VE and CoQ8 inhibited O2.- generation of neutrophils stimulated by a protein kinase C mediated process monitored by cytochrome c reduction and spin trapping methods. The inhibitory action was observed not only with alpha-tocopherol, but also with beta-, gamma-, delta-tocopherols and with tocol which is a chemical similar to VE but lacking methyl groups on the chromanol ring structure and which is not a radical scavenger. By contrast, no inhibition was observed with 2-carboxy-2, 5, 7, 8-tetramethyl-6-chromanol (CTMC, trolox) or 2, 2, 5, 7, 8,-pentamethyl-6-chromanol (PMC) which are water soluble VE derivatives having radical scavenging activity. Compounds having a similar isoprenoid chain, such as CoQ, also have inhibitory activity on PKC-dependent O2.- generation of neutrophils. The inhibitory activity of CoQ derivatives is dependent on the length of the unsaturated isoprenoid chain. CoQ derivatives having 16, 24 and 32 carbon isoprenoid chains corresponding to CoQ4, 6, and 8 inhibited O2.- generation but 4 and 40 carbon isoprenoid chains corresponding to CoQ2 and 10 had no inhibitory activity on O2.- generation. Alpha-tocopherol and CoQ inhibited PKC activity but the ID50 for O2.- generation and PKC activity was different for each compound. However, no direct relationship between VE content and O2.- generation of neutrophils was observed. These results suggest that isoprenoids of VE and CoQ participate in the inhibition of the NADPH oxidase activation system through modulation of the neutrophil membrane probably by the inhibition of PKC.

Animals↗
PubMed1996

MR pancreatography: technique and applications.

Magnetic resonance cholangiopancreatography (MRCP) is a diagnostic method that uses three-dimensional data sets for projection images, as well as arbitrary cross-sectional images, of the pancreatic ducts. The method is simple, not uncomfortable, and requires no contrast media. Magnetic resonance cholangiopancreatography (MRCP) was initially developed as a substitute for ERCP for diagnosis of pancreatic disorders such as neoplasm and chronic pancreatitis, but the method offers advantages other than safety and flexibility. MRCP may be the diagnostic method of choice when ERCP is contraindicated or fails. Imaging after injection of secretin may add functional information to MRCP that may reflect one aspect of pancreatic exocrine physiology. Adequate diagnostic evaluation of acute pancreatitis, pancreatic trauma, and mucinous ductal ectasia may also be feasible. Innovations such as fast sequences with breath-holding, receiver multicoils, high-power gradient systems, and postprocessing will further refine the technique. Optimized MRCP could limit indications for diagnostic endoscopic pancreatography substantially.

Fourier Analysis↗
PubMed1996

Nitric oxide, a physiological modulator of mitochondrial function.

The effect of nitric oxide (NO) on the energy transfer reactions of mitochondria was examined under different oxygen tensions. Mitochondrial functions, such as respiration, ATP synthesis and regulation of membrane potential, were inhibited by NO in a concentration-dependent manner. In the presence of various substrates, NO also inhibited uncoupled respiration in an oxygen concentration-dependent manner. The inhibited function recovered completely at certain times after adding NO. When added to mitochondrial suspensions, NO disappeared rapidly from the medium and more rapidly at high oxygen tensions than at low oxygen tensions as determined by the formation of methemoglobin and EPR methods. From these results it is concluded that NO might play an important role in the regulation of mitochondrial functions particularly under low oxygen concentrations.

Animals↗
PubMed1995

Inhibition of neutrophil superoxide generation by hypericin, an antiretroviral agent.

We previously reported that phorbol 12-myristate 13-acetate (PMA)-induced superoxide (O2.-) generation of neutrophils was inhibited by hypericin, a photosensitizing pigment found in St. Johnswort (herb Hypericin triquetrifolium Turra), via a mechanism involving protein kinase C (PKC). To obtain further insights into the mechanism of inhibition, the effects of hypericin on stimulation-dependent O2.- generation and related enzymes of neutrophils were investigated. Hypericin inhibited O2.- generation of neutrophils induced by PKC-dependent and -independent stimuli in a light- and concentration-dependent manner. Oxygen was required for the light-dependent inhibition by hypericin. NADPH oxidase activity in a cell-free system and TNF-alpha-induced tyrosyl phosphorylation of neutrophil proteins were also inhibited by hypericin in a concentration- and light-dependent manner. However, tyrosine kinase of p60src, an enzyme not bound to a membrane, was not inhibited either in the light or in the dark. Oxygen uptake of neutrophils by photosensitization with hypericin resulted in the formation of singlet oxygen (1O2), O2.-, and hydroxyl radical (.OH) and enhanced lipid peroxidation. The formation of 1O2 was inhibited by azide, a quencher of 1O2, but not by desferrioxamine (DSF), a ferric ion chelator. By contrast, both generation of .OH and lipid peroxidation were inhibited by DSF but not by azide. Furthermore, PMA-induced O2.- generation inhibited by hypericin partially recovered in the presence of azide but not DSF. These results suggested that the light-dependent inhibition of O2.- generation by hypericin might be due to inhibition of tyrosine kinase, PKC, and NADPH oxidase via an oxygen-dependent mechanism, possibly through both Type I and II photosensitization mechanisms.

Anthracenes↗
PubMed1995

Oxygen-dependent regulation of mitochondrial energy metabolism by nitric oxide.

To elucidate the role of nitric oxide (NO) in the regulation of mitochondrial function, the effect of NO on energy transfer reactions was examined under different oxygen tensions. Mitochondrial respiration was remarkably inhibited by NO resulting in the inhibition of ATP synthesis in a concentration-dependent manner. In the presence of succinate, respiration, respiratory control by ADP, and ATP synthesis recovered completely at certain times after adding NO. The inhibitory action of NO continued significantly longer under physiologically low oxygen concentrations (such as the cytosolic level) than at high concentrations. In the presence of various substrates, such as pyruvate malate, succinate, and ascorbate tetramethyl paraphenylenediamine, NO also inhibited the uncoupled respiration in an oxygen- and concentration-dependent manner. The inhibition of respiration by NO was stoichiometrically suppressed by oxyhemoglobin. When added to a mitochondrial suspension, NO rapidly disappeared from the medium particularly at high oxygen tension. However, the rate of NO disappearance was significantly lower under low oxygen tension. Thus, under cytosolic oxygen concentration, NO might play an important role in the regulation of mitochondrial energy metabolism.

Adenosine Triphosphate↗
PubMed1995

Effect of the antiretroviral agent hypericin on rat liver mitochondria.

The photosensitizing effect of hypericin (HY), an antiretroviral agent, on the functions of isolated rat liver mitochondria has been investigated. The respiratory control ratio (RCR), ADP/O and membrane potential of mitochondria were decreased by HY in a light-dependent manner. Uncoupled respiration of mitochondria in the presence of succinate was also inhibited by HY in a light-dependent manner. The ID50 of hypericin for these inhibitions was approximately 0.5 microM. These inhibitory effects of HY were not observed when photosensitization was conducted under anaerobic conditions and were not affected by desferrioxamine (DSF) or superoxide dismutase (SOD). Upon photosensitization of HY, mitochondria consumed oxygen in the absence of respiratory substrate with concomitant formation of thiobarbituric acid reactive substance (TBARS). The amount of oxygen consumed was 100-times greater than that of TBARS formed. The oxygen uptake was partially inhibited by NaN3, and formation of TBARS was inhibited by DSF. Upon photosensitization of HY in the presence of mitochondrial membranes, the electron spin resonance (ESR) signal of 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO/.OH) was increased by a mechanism which was suppressed by DSF. An ESR signal for singlet oxygen bound to 2,5-dimethylfuran, 2,2,6,6-tetramethyl-4-piperidone (TEMP) was also detected under light in the presence of mitochondria. This signal of the TEMP-N-oxyl radical (TEMPO) was decreased by azide, which physically quenches singlet oxygen, but was increased by DSF. These results indicate that HY might inhibit mitochondrial functions by a type II photodynamic mechanism but that lipid peroxidation of biological membranes through an active oxygen-mediated photodynamic mechanism is not involved.

Animals↗
PubMed1995

Acute hemodynamic effects of intravenous bolus injection of ionic and nonionic magnetic resonance contrast media.

RATIONALE AND OBJECTIVES: With the development of fast magnetic resonance (MR) imaging, bolus injection of contrast media is often required. We evaluated the acute hemodynamic effects of intravenous (i.v.) bolus injection of two MR contrast media: ionic gadopentetate dimeglumine and nonionic gadoteridol. METHODS: Twenty normal rats were anesthetized, and the left ventricular pressure (LVP), right atrial pressure (RAP), peripheral arterial pressure (PAP), positive rate pressure development (dP/dt) of the left ventricle, and heart rate were continuously monitored up to 10 min after bolus injections of 0.1, 0.3, and 0.5 mmol/kg of either media. RESULTS: Bolus injections of gadopentetate dimeglumine induced temporal reduction of the blood pressure (the peak LVP was -25.0% at 0.5 mmol/kg and -13.2% at 0.3 mmol/kg). At the injected doses of 0.5 and 0.3 mmol/kg, the systolic PAP, mean PAP, and dP/dt were reduced. The lowest peak systolic LVP was observed at around 20 sec after injection. Those suppressed values returned to the control values within 120 sec. Injection of high doses of gadoteridol caused a temporal increase in the peak systolic LVP (9.2% at 0.5 mmol/kg and 7.4% at 0.3 mmol/kg), systolic PAP, and dP/dt. Approximately 15 sec after injection, the highest peak systolic LVP was observed, and within 30 sec the value normalized. With both ionic and nonionic contrast media, a dose of 0.1 mmol/kg did not cause significant changes in hemodynamics. CONCLUSION: In normal rats, bolus i.v. injection of high-dose gadopentetate dimeglumine has negative hemodynamic effects; gadoteridol produces mild positive effects.

Analysis of Variance↗
PubMed1995

Benign renal tumors detected among healthy adults by abdominal ultrasonography.

Renal ultrasonography was performed on 17,941 healthy adults without any signs suggestive of urinary tract malignancies. Diffusely hyperechoic renal masses indicative of angiomyolipoma were found in 41 (0.23%) of them and those with echogenic image suggestive of renal cell carcinoma in 45 (0.25%). Final diagnosis of the former group included 24 angiomyolipoma, 1 renal cell carcinoma, 9 calculus and 7 normal variants. The latter group included 19 renal cell carcinomas, 1 leiomyoma, 1 cavernous hemangioma and 24 normal variants or cysts. In total, 24 (0.13%) angiomyolipomas, 20 (0.11%) renal cell carcinomas, 1 leiomyoma, and 1 cavernous hemangioma were discovered. The results indicate that asymptomatic benign renal tumors mainly consisting of angiomyolipoma are not uncommon.

Adult↗