Search PubMed⌕ Search

Biomedical subjects

T Sakata

Publications and source records attributed to T Sakata.

At least 163 records · Page 9Linked to original sources
PubMed1998

Sustained left ansae subclaviae stimulation for a 5-hour period inhibits cesium-induced ventricular arrhythmogenesis in rabbits.

The acute stimulation of the left ansae subclaviae (LAS) augments cesium chloride (Cs)- induced early afterdepolarizations (EADs) and ventricular arrhythmias. However, the effect of sustained cardiac sympathetic nerve stimulation on Cs-induced arrhythmogenesis remains to be elucidated. Three protocols were used. In protocol A, seven rabbits received continuous LAS stimulation for 5 h (study group), and were then given bolus injections of Cs at 5-min intervals (initial dose 1.5 mmol/kg, followed by repetitive doses 1 mmol/kg). Another eight rabbits received the same dose of Cs after a 5-h observation period without LAS stimulation (control group). The effects of 2 h of LAS stimulation were also assessed in five rabbits of each group. In protocol B, a bolus injection of Cs (1 mmol/kg) was administered during atrial pacing (cycle length: 250 ms) after a 5-h period with (study group, n = 5) or without (control group, n = 5) LAS stimulation, and the amplitude of Cs-induced EADs was measured. In protocol C, a bolus injection of isoproterenol (0.05 mg/kg) was given after a 5-h period with (study group, n = 5) or without (control group, n = 5) LAS stimulation to assess the sensitivity to beta-adrenergic stimulation. In protocol A, the cumulative doses of Cs required for the induction of ventricular tachycardia (VT) and fibrillation (VF) were significantly greater in the study group than in the control group (4.4 +/- 0.1 v 2.8 +/- 0.3 mmol/kg for VT, P<0.05; 5.8 +/- 0.3 v 4.1 +/- 0.4 mmol/kg for VF, P<0.05). However, 2 h of LAS stimulation did not influence the cumulative doses of Cs required for the induction of VT and VF. In protocol B, the amplitude of Cs-induced EADs was significantly lower in the study group than in the control group. In protocol C, the increase in rate-pressure product by isoproterenol was significantly less in study than in control groups (3492 +/- 612 v 6504 +/- 829, P<0.05). These results suggest that sustained LAS stimulation exerts a protective effect against Cs-induced arrhythmogenesis in the rabbit heart, which may be partially explained by desensitization to the beta-adrenergic stimulation.

Action Potentials↗
PubMed1998

Different concentrations of two small stress proteins, alphaB crystallin and HSP27 in human urological tumor tissues.

Concentrations of two small stress proteins, alphaB crystallin and the 27-kDa heat shock protein (HSP27) were quantitated in tissues of the human normal genitourinary system and their tumors. Levels of HSP27 in renal cell carcinomas (mean +/- SE: 1450+/-262 ng/mg protein, n = 15) were significantly higher than in normal kidney (the cortex: 540+/-99 ng/ mg protein, n = 13; the medulla: 600+/-106 ng/mg protein, n = 13) while those of alphaB crystallin tended to be increased without statistical significance. These findings were similar to those previously reported for renal cell tumors chemically induced in rats. Concentrations of alphaB crystallin in prostatic carcinoma tissues (410+/-129 ng/mg protein, n = 10) were also significantly higher than in benign prostatic hyperplasia (54+/-12 ng/mg protein, n = 14), whereas alphaB crystallin levels in testicular tumors including seminomas (2.1+/-0.8 ng/mg protein, n = 11) and non-seminomas (5.2+/-2.3 ng/mg protein, n = 9) were significantly lower than in normal testicular tissues (29.7+/-6.2 ng/mg protein, n = 5). Both alphaB crystallin and HSP27 could be immunohistochemically localized in the normal kidney and renal cell carcinoma tissues.

Animals↗
PubMed1998

Kinetics of sevoflurane action on GABA- and glycine-induced currents in acutely dissociated rat hippocampal neurons.

Effects of a new kind of volatile anaesthetics, sevoflurane, on GABA- and glycine-gated chloride current (ICl) were examined in single pyramidal neurons acutely dissociated from the rat hippocampal CA1 region, using the voltage-clamp mode of the nystatin-perforated patch-clamp technique. Rapid application of sevoflurane-induced ICl by itself, with the time to peak reduced as the sevoflurane concentration was increased from 10(-3) to 3 x 10(-3) M. Although a pretreatment with 10(-3) M sevoflurane enhanced the peak amplitude of GABA (3 x 10(-6) M)-induced ICl and suppressed the peak amplitude when the GABA concentration was increased to 10(-4) M, the pretreatment decreased the time to peak of the ICl induced by any concentration of GABA (from 3 x 10(-6) to 10(-4) M). The treatment also accelerated the decay phase of the GABA-induced ICl. On the other hand, sevoflurane suppressed the peak ICl induced by 3 x 10(-5) M glycine in a concentration-dependent manner. In the presence of 3 x 10(-4) M sevoflurane, the peak amplitude of the glycine-induced ICl was decreased without changes in EC50 or Hill coefficients. Pretreatment with 10(-3) M sevoflurane did not affect the time to peak of the ICl induced by any concentration of glycine (from 3 x 10(-5) to 10(-3) M). Pretreatment with 3 x 10(-8) M strychnine markedly prolonged the time to peak of the glycine-induced ICl. These results suggest that sevoflurane modulated the amplitude of the GABA responses, depending on the balance of the accelerated activation and decay phases, and that sevoflurane suppressed the glycine-induced ICl in a non-competitive manner without noticeable effect on the kinetics. The reversible and differential modulation of GABA(A) and glycine receptors might underlie a part of the anaesthetic actions and less adverse clinical effects of sevoflurane.

Anesthetics, Inhalation↗
PubMed1998

Histamine modulates high-voltage-activated calcium channels in neurons dissociated from the rat tuberomammillary nucleus.

The effects of histamine on high-voltage-activated Ca2+ channels in the histaminergic neurons acutely dissociated from the rat tuberomammillary nucleus were investigated in the nystatin-perforated patch recording mode under voltage-clamp conditions. Histamine suppressed the high-voltage-activated Ca2+ channel currents in neurons which were positive for histidine decarboxylase with immunocytochemistry. The half-maximum inhibitory concentration and maximum inhibition were 2.6 x 10(-7) M and 16.6+/-1.90%, respectively. An H3 receptor agonist, R(-)-alpha-methylhistamine, mimicked the response to histamine, and thioperamide, an H3 receptor antagonist, inhibited the response to histamine. On the other hand, neither 2-methylhistamine, an H1 receptor agonist, nor dimaprit, an H2 receptor agonist, had a significant effect on the Ca2+ channel currents. Pretreatment with pertussis toxin blocked the inhibitory effect of histamine on Ca2+ channels, suggesting the involvement of Gi/Go proteins in the action of histamine. Omega-conotoxin-GVIA, omega-agatoxin-IVA, nicardipine, and omega-conotoxin-MVIIC blocked the high-voltage-activated Ca2+ channel currents by 15.6, 4.3, 27.1, and 31.2% of the total current, respectively, suggesting the existence of N-, P-, L-, and Q-type Ca2+ channels. A current that was insensitive to these blockers was also found. This residual current, "R-type", was completely suppressed by the addition of 200 microM Cd2+. Histamine significantly inhibited both the N- and P-type current components among these five types of Ca2+ channel currents. We concluded that histamine suppresses the N- and P-type Ca2+ channels in histaminergic neurons through an H3 receptor which is linked to a pertussis toxin-sensitive G-protein.

Animals↗
PubMed1998

Production of monoclonal antibody against histamine and its application to immunohistochemical study in the stomach.

A monoclonal antibody against histamine has been produced. A histamine-haemocyanin conjugate prepared using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a coupling agent was used for immunizing mice. Immunized mice were sacrificed to prepare monoclonal antibody using a hybridoma technique. On immunospot assay, the hybridoma culture supernatant containing a monoclonal antibody was capable of detecting 50 pmol of histamine. Using this antibody, we examined the cellular localization of histamine-like immunoreactivity in the stomach of normal or alpha-fluoromethylhistidine-treated rats and mice. Immunoreactive cells were abundant in the gastric mucosal layer. These positive cells were often located in the basal half of the fundic gland but were rare in the pyloric gland. The cells, small or medium in size, spindle or cone in shape, were intermingled with immunonegative epithelial cells. In the cytoplasm of the positive cells, granular reaction products were densely deposited. In addition, a few positive cells, identified as mast cells by Toluidine Blue staining, were distributed mainly in the submucosal and muscular layer. The antibody preabsorbed with 10 mM histamine gave no positive immunostaining. For pharmacological study, some rats were injected six times with c-fluoromethylhistidine every 8 h. In these rats, positive cells except mast cells were no longer detected. In conclusion, the monoclonal antibody produced appears to be highly specific for histamine. Its application in immunohistochemistry should provide a powerful tool for analysing the roles of histamine in enterochromaffin-like or mast cells in the stomach.

Animals↗
PubMed1998

Amino acid metabolism of bovine blastocysts derived from parthenogenetically activated or in vitro fertilized oocytes.

The uptake and synthesis of 19 amino acids by fresh or frozen-thawed bovine blastocysts produced by parthenogenesis (PT) or in vitro fertilization (IVF) were compared in the present study. Fresh blastocysts, 180 h after IVF or PT activation, and frozen-thawed blastocysts, 168 h old and cultured for 12 h post-thawing, were cultured in synthetic oviduct fluid medium (SOFM) containing polyvinyl alcohol (PVA) with both essential and non-essential amino acids (EAA and NEAA, respectively) (Medium 1: M1) or SOFM containing PVA with only EAA (Medium 2: M2). In Experiment 1, when fresh or frozen-thawed PT blastocysts were cultured in M1, the uptake of glutamate (in fresh only), aspartate and arginine, and the synthesis of glutamine and alanine were significantly enhanced. In the culture with M2, serine, asparagine, glutamate, glutamine, glycine, arginine and alanine were significantly taken up. It was found that the glutamine concentrations was significantly higher (P < 0.001) in the culture medium drops containing embryos than in the drops without embryos. In Experiment 2, when PT blastocysts were cultured in M1, the uptake of aspartate and synthesis of alanine were greater (P < 0.01) than those by IVF blastocysts. When M2 was used, a significant (P < 0.01) production of serine, asparagine, glutamate, glutamine and alanine, and the uptake of arginine by PT blastocysts were observed. In Experiment 3, when IVF blastocysts were cultured in M1, fresh blastocysts depleted more aspartate and glutamate, and produced more glutamine and alanine than frozen-thawed blastocysts. When cultured in M2, frozen-thawed blastocysts depleted more threonine (P < 0.01) than fresh blastocysts. These results indicate that the uptake and synthesis of amino acids were different in fresh or frozen-thawed bovine blastocysts derived from PT or IVF. These differences in amino acid metabolism may be related to the viability of the blastocysts.

Alanine↗
PubMed1998

Dietary fructooligosaccharides prevent osteopenia after gastrectomy in rats.

Postgastrectomy osteopenia is observed generally in humans. Fructooligosaccharides increase the absorption of calcium from the large intestine of healthy rats. Thus, we have examined whether they stimulate calcium absorption and prevent osteopenia in rats following total gastrectomy. Rats were subjected to either a sham surgical operation or Billoth II gastrectomy. Seven rats from each surgical treatment group were fed a control diet, and another seven rats of each treatment group were fed a diet containing fructooligosaccharides (75 g/kg diet) for 4 wk. For 5 d each week, feces were collected, and the calcium and phosphorus contents were measured for calculation of the absorption of these minerals. At the end of the experiment, the rats were killed and bones were collected. The net calcium absorption, calcium content and bone mineral density of the femur and tibia in gastrectomized rats fed the control diet were significantly less than those in sham-operated rats fed control diet. The net calcium absorption in rats fed the fructooligosaccharides diet was greater than that in rats fed control diet. Moreover, dietary fructooligosaccharides prevented the decrease in the calcium content and bone mineral density in gastrectomized rats. Dietary fructooligosaccharides enhanced calcium absorption and prevented the changes indicative of postgastrectomy osteopenia such as decreases in bone calcium content and bone mineral density in gastrectomized rats.

Absorption↗
PubMed1998

Stimulation of epithelial cell proliferation of isolated distal colon of rats by continuous colonic infusion of ammonia or short-chain fatty acids is nonadditive.

Dietary fibers accelerate colonic epithelial cell proliferation at least in part by modulating bacterial metabolism in the large intestine. Ammonia and short-chain fatty acids (SCFA) are major metabolites of hindgut bacteria and are believed to affect epithelial cell kinetics of the colon. However, the effect of luminal ammonia itself and the possible interaction of ammonia with SCFA on colonic epithelial cell proliferation have not yet been studied. The colon of rats was surgically isolated and continuously administered infusates with saline, ammonia, SCFA or both into the isolated colon for 7 d in a two-way factorial design. On d 7, vincrystine sulfate was administered intravenously to cause metaphase arrest. The activity of epithelial cell proliferation in the distal colon was estimated by using a stathmokinetic method and by histologic examination. The crypt size was significantly larger in rats given infusates containing SCFA than in rats given infusates without SCFA. Infusion of ammonia or SCFA significantly stimulated colonic epithelial cell proliferation compared with the saline infusion. Infusion of both ammonia and SCFA resulted in accumulated mitoses per crypt that did not differ from the other three infusions although the value tended to be lower than when SCFA alone were infused. Thus, stimulation of epithelial cell proliferation by ammonia and SCFA is not additive, and the interaction between them should be considered when the effects of dietary fibers on gut epithelial proliferation are investigated.

Ammonia↗
PubMed1998

A polymorphism of angiotensinogen gene codon 174 and coronary artery disease in Japanese subjects.

The relationship between coronary artery disease (CAD) and polymorphisms of genes encoding angiotensinogen (AGT) and angiotensin converting enzyme (ACE) was analyzed in Japanese subjects. One hundred and four patients with CAD and 170 healthy subjects were enrolled in the study. CAD was defined as having a luminal diameter stenosis > or =50% in at least one of three major coronary arteries by coronary angiography. The genotypes (determined by polymerase chain reaction) of AGT gene codon 174 were not significantly associated with CAD in the total study population. However, the frequency of T/T homozygotes of AGT codon 174 was significantly higher in CAD patients compared to controls in each of three subgroups: 1) body mass index (BMI) below the median value of 24.1 kg/m2; 2) not more than two CAD risk factors out of five (hypercholesterolemia, hypertension, diabetes mellitus, smoking, and family history of CAD); and 3) the ACE I/I genotype. The M/M genotype of AGT codon 235 was negatively associated, and the ACE D/D genotype was positively associated, with CAD in the total study population. Our results indicate that the T/T genotype of AGT codon 174 may be a risk factor for CAD in Japanese individuals with low BMI, lesser CAD risk factors, or ACE I/I genotype.

Aged↗
PubMed1998

Elucidating the mechanism of cesium-induced sustained monomorphic ventricular tachycardia in rabbits.

The mechanisms of sustained ventricular tachycardia (VT) induced by large cumulative dose of cesium chloride (Cs) remains unclear. Seven anesthetized rabbits were intravenously injected with Cs (1 mmol/kg) 3 times at 20-min intervals. The surface ECG and monophasic action potential of the left ventricular endocardium were simultaneously recorded. In another 12 rabbits, transmembrane action potentials of right ventricular muscles were recorded with glass microelectrodes. In experiments in vivo, sustained monomorphic VT was induced after the third injection of Cs, whereas the early afterdepolarization (EAD)-related nonsustained polymorphic VT was induced after the second injection. Overdrive pacing during the sustained VT resulted in postdrive acceleration. The pacing and recovery cycle lengths showed an inverse relation. In experiments in vitro, preparations were superfused with Tyrode's solution containing 7.5 mM Cs. Cs initially induced EADs. Additional exposure to Cs depolarized the membrane potential, which consequently attained threshold, producing spontaneous activities. Further exposure resulted in an induction of sustained rhythms that were accelerated by overdrive pacing. Our results indicate that the sustained rhythms at low membrane potential induced by a long exposure to Cs in vitro may underlie an electrophysiologic mechanism for the sustained VT induced after large cumulative dose of Cs in vivo.

Action Potentials↗
PubMed1998

Paradoxically shortened QT interval after a prolonged pause.

We analyzed Holter ECG recordings in 15 patients with episodes of prolonged RR intervals > 2.5 seconds. In 13 patients, the QT interval showed a linear prolongation when RR interval was < 1.5 seconds and became relatively flat at longer RR intervals. In the remaining two patients, the QT and RR intervals were correlated within physiological range of RR intervals. However, at longer RR intervals, the QT interval was unexpectedly shortened and constant. The paradoxically shortened QT interval observed in the present 2 cases may indicate an abnormal adaptation of repolarization time to an abrupt increase in the preceding RR intervals.

Adult↗
PubMed1998

Clinical suppression of bradycardia dependent premature ventricular contractions by the potassium channel opener nicorandil.

OBJECTIVE: To assess the clinical antiarrhythmic effect of nicorandil, a potassium channel opener; on premature ventricular contractions. DESIGN AND PATIENTS: The effect of oral nicorandil (15 to 60 mg daily for four weeks) on premature ventricular contractions was investigated in 20 patients (11 female, nine male, mean (SD) age 63 (17) years) who underwent 24 hour ambulatory ECG. Patients were classified into two groups based on the relation between the frequency of premature ventricular contractions and heart rate: (1) those with a positive correlation (n = 9); and (2) those with a bidirectional correlation (n = 11), characterised by an increased frequency of premature contractions at low heart rates and a decreased frequency at high heart rates. RESULTS: Nicorandil reduced the frequency of premature ventricular contractions by 75% in five patients in group 2, but was not effective in any patient in group 1. The heart rate at which the frequency of premature ventricular contractions peaked was significantly lower in the five responders in group 2 than in the six non-responders (63.2 (3.7) v 76.3 (12.4) beats/min, p < 0.05). CONCLUSIONS: Nicorandil may suppress premature ventricular contractions when they occur mainly at a low heart rate.

Adult↗
PubMed1998

Role of circadian rhythmicity in the heart rate variability preceding non-sustained ventricular tachycardia.

The difference in sympathovagal activity preceding non-sustained ventricular tachycardia (NSVT) was examined between patients with and without a circadian rhythm. Thirty-three patients' Holter monitoring data (41 NSVT episodes) were analyzed regarding the frequency domain measures (low-frequency component [LF: 0.04-0.15 Hz], high-frequency component [HF: 0.15-0.4 Hz], and the ratio of LF to HF [LF/HF]) for each 15-min average from 120 min before each episode of NSVT. The presence of a circadian rhythm was accepted when the rhythm adaptation was significant by cosinor analysis and the acrophase was located at night (22.00-06.00h) in HF (HF-positive group, n=17), and during the daytime (10.00-20.00h) in LF/HF (LF/HF-positive group, n=12). The negative groups were identified by the absence of a circadian rhythm (HF-negative group, n=16; LF/HF-negative group, n=21). The serial changes in the HF power before NSVT were significantly different between the HF-positive and -negative groups (p<0.05). The HF increased from 75-60 min before NSVT in the HF-positive group, whereas the HF decreased from 60-45 min in the HF-negative group. The serial changes in the LF/HF ratio were not significantly different between the LF/HF-positive and -negative groups. Thus, the circadian rhythmicity of vagal activity seems to have an important role in the genesis of NSVT.

Aged↗
PubMed1998

Vagal modulation of ventricular tachyarrhythmias induced by left ansae subclaviae stimulation in rabbits.

Previous evidence has shown that vagal nerve activity modulates ventricular arrhythmias in patients and in animal models. However, the effects of direct vagus nerve stimulation on ventricular tachyarrhythmias brought by direct sympathetic nerve stimulation have not been elucidated. In the present study, the effects of electrical stimulation of the left cervical vagus nerve on ventricular tachycardia (VT) which was induced by electrical stimulation of the left ansae subclaviae (LAS) in rabbits were assessed. Monophasic action potentials (MAPs) of the left ventricular endocardium were recorded simultaneously with surface ECG. In 27 rabbits tested, the stimulation of LAS induced VT in 19 rabbits. Polymorphic VT (PVT) was induced in 14 rabbits (PVT group), whereas monomorphic VT (MVT) was induced in 5 rabbits (MVT group). Vagus nerve stimulation during the sympathetically-induced PVT led to a restoration of sinus rhythm in 10 of 14 rabbits, while that during the sympathetically-induced MVT did not restore sinus rhythm in any of the 5 rabbits. Vagus nerve stimulation during the stimulation of LAS, which was of subthreshold intensity for the induction in VT, did not result in an induction of PVT in any of the 14 rabbits in the PVT group, while it induced slow MVT in 3 of 5 rabbits in the MVT group. These results indicate that vagus nerve stimulation preferentially exerts protective antiarrhythmic effects against PVT induced by sympathetic neural stimulation in this model, while it occasionally induces slow MVT under conditions in which sympathetic nerve activity in potentially elevated.

Animals↗
PubMed1998

Anatomically guided radiofrequency catheter ablation of atrial reentrant tachycardia.

Atrial reentrant tachycardia (ART) was ablated in an anatomically guided approach. Five patients with ART underwent 2 linear incisions without careful pace or activation mapping. One line was from an atrial activation site earlier than P wave onset to the nearest fixed anatomic conduction barrier, i.e., the inferior vena cava or coronary sinus ostium. The other line was made just above or closely crossed the first line vertically. Mean application time was 29 +/- 19 minutes, and the application energy was 14,001 +/- 12,322 joules. Mean follow-up after ablation was 15 +/- 10 months. Three patients underwent electrophysiologic study three months after and sustained ART was not induced. All patients were free of sustained tachycardia events without antiarrhythmic drugs during the postoperative clinical course. Although anatomically guided ablation for ART requires much time and energy, it is easily and effectively done without careful activation or pace mapping, and is indicated if ablation using activation mapping or entrainment technique fails to cure the ART.

Adult↗
PubMed1998

Hb Oita [alpha45(CE3)His-->Pro]: a new silent hemoglobin variant.

We describe a new alpha chain variant accidentally found in a 49-year-old female living in Usa City, Oita Prefecture, Japan. An abnormally low Hb A1c value of 2.5% (normal range: 4.8-6.3%) was found while she was treated with glucocorticoid for Fisher syndrome. The patient was also diagnosed as having an iron deficiency anemia, but otherwise showed a normal hemogram. An abnormal hemoglobin was not detectable by isoelectrofocusing and high performance liquid chromatographic methods, but appeared as a fast-moving alpha chain abnormality by urea-carboxymethyl cellulose column chromatography of the globin, from which the content of the abnormal hemoglobin was estimated at approximately 20%. The instability test of the hemolysate was normal. Structural studies demonstrated that the abnormal hemoglobin had an amino acid substitution of His-->Pro at alpha45. It is a new variant and was named Hb Oita or alpha45(CE3) His-->Pro. Additionally, sequence analysis showed a nucleotide change from A-->C at the second base in the 45th codon of the alpha2 gene, CAC(His)-->CCC (Pro). The beta/alpha ratio was 0.51 (normal range: 0.9-1.2). Her mother and a son did not have the abnormal hemoglobin variant; her father was deceased and no sample was available to verify the inheritance of the variant in this kindred.

Female↗
PubMed1998

Satiation and masticatory function modulated by brain histamine in rats.

Both the ventromedial hypothalamus (VMH) and the mesencephalic trigeminal sensory nucleus (Me5) are densely innervated by histaminergic neurons. The depletion of neuronal histamine (HA) from the Me5 by the bilateral microinfusion of 448 nmol/rat alpha-fluoromethylhistidine (FMH), a specific suicide inhibitor of histidine decarboxylase, reduced the eating speed and prolonged meal duration, while leaving the meal size unaffected. HA depletion from the VMH increased the size of the meal and prolonged its duration, but not the eating speed. When the HA turnover rate was measured at 15 min after the scheduled feeding following fasting for less than 24 hr, the rate increased in the region including the Me5, but not in the hypothalamus. The turnover rate reached higher levels at 60 min in both regions. Gastric intubation of an isocaloric liquid diet or an equivolume of water with the liquid diet abolished the increase in HA turnover both in the Me5 region and the hypothalamus. The present findings indicate that brain HA thus modulates satiation through both the VMH and masticatory function as well as due to the action of the Me5. The HA function activated by mastication began earlier in the Me5 and later in the hypothalamus due to a signal originating from the oral proprioceptors and initiated by chewing.

Animals↗