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N Sasaki

Publications and source records attributed to N Sasaki.

At least 163 records · Page 9Linked to original sources
PubMed1999

Early stage-stress relaxation in compact bone.

The early stage of stress relaxation, up to 10 s after strain application, in compact bone was investigated in order to find the limit of the applicability of the empirical equation (Sasaki et al., 1993. Journal of Biomechanics 26, 1369-1376), E(t) = E0{A1exp[-(t/tau1)beta]+A2exp(-t/tau)}, A1+A2 = 1, 0<beta< or =1, where E0 is the relaxation modulus value at t = 0, A1 and A2 are portions of the first term (the KWW relaxation) and the second term (the Debye relaxation), respectively, and tau1 and tau2 are relaxation times of respective relaxation processes. The relaxation modulus was generally well fitted to the empirical equation, although magnification revealed that in the short-time response region there was an inconsistency between the empirical equation and the measured data. The residual deviation increases with the decrease in time of the initial datum point which was used for the regression analysis. This tendency was concluded to be due to material properties. These results indicate the existence of a new relaxation in the short time response region (t<2-3 s) of the stress relaxation process that cannot be described by the empirical equation.

Animals↗
PubMed1999

Time-resolved X-ray diffraction from tendon collagen during creep using synchrotron radiation.

In order to understand the molecular mechanism of relaxation phenomena in collagenous tissue, time-resolved, small-angle X-ray diffraction measurements were performed on bovine Achilles tendon collagen under creep. A tension-induced increase in the 67 nm period (D-period) was observed, and the strain in the D-period, epsilon D, was found to be almost proportional to the external force per unit cross-sectional area (average stress) of the specimen. With an increase in epsilon D, a change in the ratio of intensities of the third-order reflection peak of the D-period to that of the second-order peak was also observed. The increase in epsilon D was decomposed into three elementary processes of D-period deformation, which are presented on the basis of the Hodge-Petruska model: (1) molecular elongation, (2) increase in gap region, and (3) relative slippage of lateral adjoining molecules. Up to 8 MPa of average stress, the contribution to epsilon D originated mostly from only mode (1). At more than 10 MPa of average stress, modes (2) and (3) also contributed to fibril elongation. For epsilon D by molecular elongation (mode (1)), the time dependence of the D-period change in the immediate response region is a sharply shaped step function, while the contribution to epsilon D by molecular rearranging modes gives a slight creep nature at the immediate response region in the time dependence of epsilon D. Because this creep nature is observed at the immediate response, it is related qualitatively to the KWW function in a stress-relaxation modulus of collagenous tissue observed in an immediate response region (Sasaki et al. (1993). Journal of Biomechanics 26, 1369-1376). The elementary process of KWW-type relaxation is concluded to be related to the tension-induced molecular rearrangement within a D-period.

Achilles Tendon↗
PubMed1999

Mechanism of inhibition of the Na current by tocainide in guinea-pig isolated ventricular cells.

Tocainide blocked the Na current (I(Na)) in ventricular myocytes in either a tonic or a phasic block manner, having a higher affinity for the inactivated state (K(di) = 18 microM) than for the rested state (Kd(rest) = 606 microM). The degree of phasic block was enhanced and the onset of phasic block was faster with an increase in pulse duration as well as at less-negative holding potential (HP). The recovery-time constant from the phasic block of I(Na) induced by tocainide was independent of either the HP or the removal of fast inactivation. After removal of fast inactivation, tocainide showed the pulse-duration dependency of phasic block but not the voltage dependency. These results suggest that tocainide could bind to the inactivated-state receptor through the hydrophilic pathway and leave the receptor through the hydrophobic pathway, producing the tonic and phasic block of I(Na).

Animals↗
PubMed1999

Comparison of sedative effects of medetomidine-midazolam, acepromazine-butorphanol and midazolam-butorphanol in dogs.

Sedative effects of medetomidine at 20 micrograms/kg and midazolam at 0.3 mg/kg (MM), acepromazine at 0.05 mg/kg and butorphanol at 0.2 mg/kg (AB), and midazolam at 0.1 mg/kg and butorphanol at 0.2 mg/kg (MB) were compared in dogs. All dogs given MM were laterally recumbent within 11 min of the administration of the drugs, and this combination also induced deep sedation accompanied by analgesia and muscle relaxation, and strongly depressed arousal reactions to external stimuli. However, undesirable effects such as bradycardia and decreased respiration were also observed in dogs given MM. Six of seven dogs given AB were laterally recumbent within 16 min of the administration of the drugs, and this combination induced relatively deep sedation but only a mild depression of arousal reactions to external stimuli. MB induced mild or moderate sedation with relatively large differences in effects among individuals. The recovery from sedation in each group was smooth and total recovery times were not significantly different.

Acepromazine↗
PubMed1999

Effects of permanent tracheostomy on respiratory reflexes to lung inflation and capsaicin in sevoflurane-anaesthetized dogs.

The aim of this study was to evaluate the effects of permanent tracheostomy on baseline breathing, reflex responses to lung hyperinflation (1.5 kPa) and right atrial capsaicin injection (5 micrograms/kg) before and at 3 and 5 weeks after tracheostomy in sevoflurane-anaesthetized spontaneously breathing dogs (n = 6). In all observation periods, apnoeic responses, represented by an increase in expiration time after lung inflation and right atrial capsaicin injection, were consistently observed to be a result of the Hering-Breuer inflation reflex and the pulmonary C-fibre chemoreflex. Investigation at 3 and 5 weeks after tracheostomy revealed no significant evidence of changing baseline breathing pattern or reflex responses to lung inflation and capsaicin in any ventilatory variable (inspiration time, expiration time, tidal volume, expired ventilation, and end-tidal PCO2) from levels recorded before surgery. These results indicate that permanent tracheostomy, at least up to 5 weeks, does not affect the baseline breathing pattern, the Hering-Breuer inflation reflex or the pulmonary C-fibre chemoreflex. Further, our investigation provides a useful canine model in respiratory physiology.

Anesthetics, Inhalation↗
PubMed1999

Comparison of cardiopulmonary effects of medetomidine-midazolam, acepromazine-butorphanol and midazolam-butorphanol in dogs.

Cardiopulmonary effects of intramuscular administration of medetomidine-midazolam at 20 micrograms/kg and 0.3 mg/kg, respectively (MM), acepromazine-butorphanol at 0.05 and 0.2 mg/kg, respectively (AB), and midazolam-butorphanol at 0.1 and 0.2 mg/kg, respectively (MB), were compared in dogs. MM produced relatively large cardiovascular changes such as bradycardia, hypertension, a decrease in cardiac output and vasoconstriction. AB produced moderate cardiovascular changes. Hypotension was observed within 5 min after administration and the mean arterial blood pressure decreased by 30% at 20 min after administration. MB produced decreases in arterial blood pressure and cardiac output, but these changes were small and, of the combinations evaluated in this study, MB had the mildest cardiovascular effects.

Acepromazine↗
PubMed1999

Changes in cell volume induced by ion channel flux in guinea-pig cardiac myocytes.

1. The cell width of guinea-pig ventricular myocytes was measured using an optic device during patch-clamp experiments and the relationship between the ion channel flux and changes in cell volume was examined. 2. On superfusing myocytes with 50, 70, 150 and 200% osmotic solutions, the relative cell width changed to 121.1 (n = 4), 110.8 (n = 27), 87.1 (n = 6) and 82.6% (n = 6) of control, respectively. Changes in cell length were less than 2% in these test solutions. 3. The application of 300 nmol/L isoprenaline to myocytes swollen in the 70% hypotonic solution induced a decrease in cell width from 111.2 to 106.2% (n = 13). The application of isoprenaline in the isotonic solution also induced a decrease in cell width to 96.5% in eight of 13 cells. A membrane depolarization of 2-4 mV accompanied the isoprenaline-induced decrease in volume. In the remaining five cells, neither an obvious isoprenaline-induced decrease in volume nor membrane depolarization was observed. Under ruptured whole-cell voltage clamp conditions, the activation of inward isoprenaline-induced Cl- current decreased cell width. 4. Cell width was seen to either decrease or increase when a large outward or inward K+ current, respectively, was induced by shifting the holding potential or by applying 200 mumol/L pinacidil. Under gramicidin-perforated whole-cell clamp conditions, the cell width did not change, even when a large inward K+ current was induced. 5. When the test solution was applied to half of an elongated myocyte by using a micropipette, the cell width increased or decreased in the part exposed to the hypotonic or hypertonic test solutions, respectively. In contrast, in the other half of the elongated myocyte, the cell width responded in the opposite direction. 6. It is concluded that a continuous ionic flux through ion channels is capable of inducing changes in cell volume by generating a localized osmotic gradient across the cardiac sarcolemma.

Animals↗
PubMed1999

Use of scintigraphy with 99mtechnetium galactosyl human serum albumin for staging of primary biliary cirrhosis and assessment of prognosis.

BACKGROUND: Conventional models for prediction of survival in patients with primary biliary cirrhosis (PBC) are based on the results of blood tests and on the clinical condition, which may be affected by treatment. We evaluated the usefulness of hepatic receptor imaging with [99mtechnetium]-diethylenetriaminepentaacetic acid galactosyl human serum albumin (GSA) for the staging and prognosis of PBC without the need for reference to laboratory test results. METHODS: The subjects were 45 patients with PBC, 10 healthy subjects, 62 patients with chronic hepatitis and 144 patients with cirrhosis. Computer acquisition of gamma-camera data was started just before the injection of 185 MBq [99mTc]-GSA and was stopped 20 min later. Time-activity curves were generated from regions of interest (ROI) for the heart and liver. A receptor index was calculated by dividing the radioactivity of the liver ROI by that of the liver-plus-heart ROI 15 min after the injection. An index of blood clearance was calculated by dividing the radioactivity of the heart ROI 15 min after the injection by that of the heart ROI 3 min after the injection. RESULTS: The median receptor index was higher in patients with PBC than in those with cirrhosis. Among patients with PBC, the receptor index was lower in those with stage IV disease than in those in stages I, II or III. The index of blood clearance was lower in patients with PBC than in those with cirrhosis. Among patients with PBC, the index of blood clearance was higher in those with stage IV disease than in those in stages I, II or III. The receptor index was correlated significantly both to the risk score of the Mayo model and to the prognostic index of the Japanese model. The index of blood clearance was also correlated significantly to this score and prognostic index. CONCLUSIONS: Hepatic receptor imaging with [99mTc]-GSA is useful for the evaluation of hepatic functional reserve, staging of PBC and assessment of prognosis.

Asialoglycoprotein Receptor↗
PubMed1999

Plasma oestrone and oestradiol concentrations throughout gestation in cattle: relationship to stage of gestation and fetal number.

The objectives of the study were to characterise the peripheral plasma oestrone (E1) and oestradiol-17beta (E2) concentrations throughout gestation in the cow and to correlate this with the stage of gestation and fetal number. Cows (n = 10) were equally divided into two groups after non-surgical embryo transfer of in-vitro matured and in-vitro fertilised (IVM - IVF) embryos; Group 1 received a single embryo, Group 2 received twin embryos. Blood was collected about every third day from day 0 (day 0 was defined as first day of standing oestrus), then daily for the last 10 days of gestation and sampling was stopped one day post partum. Plasma E1 concentration exceeded that of E2 throughout gestation in both groups of cows. The time trend concentrations of plasma E1 were significantly affected by the stage of gestation (P < 0.01) and fetal number (P < 0.01) in the last two trimesters of gestation. The time trend concentrations of plasma E2 were significantly affected by the stage of gestation (P<0.01) but not foetal number (P = 0.09). In both groups there was marked preparturient increase in E1 and E2 concentrations. Plasma E2 profile between days 10 prepartum to parturition paralleled E1 in cows carrying a single foetus but was disparate during the same period in the twin-bearing cows. To conclude, our results indicate that although plasma E1 concentration was greater than E2 throughout gestation, both were related to the stage of gestation and that fetal number was correlated with circulating E1 levels in the last two trimesters of gestation.

Animals↗
PubMed1999

Effects of AH-1058, a new antiarrhythmic drug, on experimental arrhythmias and cardiac membrane currents.

AH-1058 is a newly synthesized antiarrhythmic agent. We investigated the antiarrhythmic and electrophysiological effects of AH-1058 in experimental arrhythmia models and isolated cardiomyocytes. In the ouabain-induced arrhythmia model of the guinea pig, pretreatment with AH-1058 (0.1-0.3 mg/kg, i.v.) delayed the appearance of premature ventricular complex (PVC) and ventricular fibrillation (VF) induced by intravenous infusion of ouabain. However, disopyramide (10 mg/kg, i.v.) delayed only that of PVC, and verapamil (1 mg/kg, i.v.) failed to affect the ouabain-induced ventricular arrhythmias. In the reperfusion-induced arrhythmia model of the rat, in which 5-min coronary occlusion and 10-min reperfusion were produced, AH-1058 (0.1-0.3 mg/kg, i.v.) inhibited the incidence of both ventricular tachycardia (VT) and VF, whereas disopyramide (5 mg/kg, i.v.) inhibited only reperfusion-induced VF. On the other hand, a higher dose of AH-1058 (1 mg/kg, i.v.) did not affect the aconitine-induced arrhythmias in rats, which were inhibited by disopyramide (5 mg/kg, i.v.). We also confirmed oral activity of AH-1058 in the reperfusion-induced arrhythmia model of the rat. AH-1058, at doses of 2-4 mg/kg, dose-dependently inhibited VT and VF. Electrophysiological experiments with patch-clamp techniques revealed that AH-1058 potently suppressed the L-type Ca2+ currents in isolated cardiomyocytes of the guinea pig. These results suggest that AH-1058 is a potent antiarrhythmic drug having a Ca2+ channel-blocking action. The antiarrhythmic profile of AH-1058 is different from that of disopyramide and verapamil.

Aconitine↗
PubMed1999

Protein expression of cell cycle regulator, p27Kip1, correlates with histopathological grade of non-Hodgkin's lymphoma.

The protein p27Kip1 is one of the cyclin-dependent kinase inhibitors that are known to play important roles in the regulation of cell-cycle progression. Low levels of p27 expression in malignant cells are associated with poor prognosis in patients with breast, lung, colorectal and gastric cancers. To determine the relation of cyclin-dependent kinase inhibitors to histopathological grades of B-cell non-Hodgkin's lymphomas, the expression of p27, cyclin D1 and cyclin E in lymph node tissues was investigated in 56 patients with B-cell non-Hodgkin's lymphomas by western blotting and immunohistochemical techniques. High levels of p27 expression were observed in most lymph node tissue samples (93%) obtained from patients with low grade B-cell non-Hodgkin's lymphomas, while expression was low in lymph node tissue taken from all patients with intermediate and high grade B-cell non-Hodgkin's lymphomas. The difference in p27 expression in lymphoma tissues was significant among the different histopathological grades of B-cell non-Hodgkin's lymphomas (P<0.01). The analysis of the survival time of patients showed that the reduction of p27 expression correlated with poor prognosis. Cyclin D1, showed a high level of expression in mantle cell lymphomas and high grade B-cell non-Hodgkin's lymphomas. Cyclin E showed limited expression in 18 of 31 lymphoma tissues. Both cyclin D1 and E protein expression were not significantly different among the grades of B-cell non-Hodgkin's lymphomas. These results demonstrate that the level of p27 expression in lymphoma tissue is an important parameter in the classification of B-cell non-Hodgkin's lymphomas and in the prediction of prognosis.

Blotting, Western↗
PubMed1999

Influence of increased abdominal pressure on steady-state cardiac performance.

The effect of steady-state increases in abdominal pressure (Pab) on cardiac performance was studied in seven acutely instrumented swine with pneumoperitoneum (PP). The animal was placed on volume-preset ventilation, and PP was created by air insufflation. Cardiac output (CO), right atrial (Pra), left atrial (Pla), pericardial (Ppe), and abdominal inferior vena cava pressures (Pivc) were measured while Pab was increased from baseline to 7.5, 15, and 30 mmHg (PP7.5, PP15, and PP30, respectively). Cardiac function curves of the right and left ventricle (RV and LV, respectively) were compared between baseline and PP30. CO presented biphasic changes, with an inital slight increase at PP7.5 followed by a fall at PP30. A significant discrepancy was observed between Pra and Pivc at PP15 and PP30, consistent with development of a "vascular waterfall." Transmural Pla (Pla - Ppe) showed parallel changes with CO, whereas transmural Pra (Pra - Ppe) exhibited a sustained increase. The RV cardiac-function curve was more depressed than was that of the LV at PP30; this suggests an increased RV afterload produced by the elevated airway pressure. These results support the hypothesis that our previously proposed concept of abdominal vascular zone conditions (M. Takata, R. A. Wise, and J. L. Robotham. J. Appl. Physiol. 69: 1961-1972, 1990) is also applicable to steady-state hemodynamic analyses. The abdominal zones appear to play an important role in determining CO, with increases in Pab, by modulating systemic venous return and the LV preload. Simultaneous measurements of Pra and Pivc may provide useful information in the hemodynamic care of patients with elevated Pab.

Abdomen↗
PubMed1999

Daily aerobic exercise improves reactive hyperemia in patients with essential hypertension.

The effects of long-term aerobic exercise on endothelial function in patients with essential hypertension remain unclear. To determine whether endothelial function relating to forearm hemodynamics in these patients differs from normotensive subjects and whether endothelial function can be modified by continued physical exercise, we randomized patients with essential hypertension into a group that engaged in 30 minutes of brisk walking 5 to 7 times weekly for 12 weeks (n=20) or a group that underwent no activity modifications (control group, n=7). Forearm blood flow was measured using strain-gauge plethysmography during reactive hyperemia to test for endothelium-dependent vasodilation and after sublingual nitroglycerin administration to test endothelium-independent vasodilation. Forearm blood flow in hypertensive patients during reactive hyperemia was significantly less than that in normotensive subjects (n=17). Increases in forearm blood flow after nitroglycerin were similar between hypertensive and normotensive subjects. Exercise lowered mean blood pressure from 115.7+/-5.3 to 110.2+/-5.1 mm Hg (P<0.01) and forearm vascular resistance from 25.6+/-3.2 to 23. 2+/-2.8 mm Hg/mL per minute per 100 mL tissue (P<0.01); no change occurred in controls. Basal forearm blood flow, body weight, and heart rate did not differ with exercise. After 12 weeks of exercise, maximal forearm blood flow response during reactive hyperemia increased significantly, from 38.4+/-4.6 to 47.1+/-4.9 mL/min per 100 mL tissue (P<0.05); this increase was not seen in controls. Changes in forearm blood flow after sublingual nitroglycerin administration were similar before and after 12 weeks of exercise. Intra-arterial infusion of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine abolished the enhancement of reactive hyperemia induced by 12 weeks of exercise. These findings suggest that through increased release of nitric oxide, continued physical exercise alleviates impairment of reactive hyperemia in patients with essential hypertension.

Analysis of Variance↗
PubMed1999

Effects of volatile anesthetics on the activity of laryngeal 'drive' receptors in anesthetized dogs.

Effects of halothane, isoflurane and sevoflurane on laryngeal drive receptor activity were studied in the afferent activity of the superior laryngeal nerve in anesthetized spontaneously breathing dogs. Of 40 single units recorded, most of them (65%) responded to the volatile anesthetics applied to the isolated larynx at a concentration of 5%. The exposure to the anesthetics resulted in either an inspiratory increase (15%), both inspiratory and expiratory decrease (54%), or both inspiratory increase and expiratory decrease (31%) responses. The average discharge frequency of the receptors tended to be decreased on inhalation of the anesthetics, where significant decreases were observed in both respiratory phases for halothane and at expiration for isoflurane, but in neither respiratory phase for sevoflurane. These results support an advantage of sevoflurane over halothane and isoflurane for induction of anesthesia to minimize the influence of the activity of laryngeal drive receptors on the breathing pattern and airway stability.

Anesthetics, Inhalation↗
PubMed1999

Measurement for breath concentration of hydrogen and methane in horses.

This study concerns the establishment of a simple testing method for breath concentration of hydrogen and methane in horses. Twenty-eight healthy thoroughbreds and 24 Arabians were used. Breath samples were collected using one-minute closed circulatory respiration through an aluminum bag filled with 10 liters of pure oxygen, which was mounted on the subjects by means of a face mask. Breath samples obtained, were analyzed by gas chromatography. A significant correlation in both hydrogen and methane levels was observed for samples collected at separate times. These findings confirmed the usefulness of our approach for testing breath concentrations of hydrogen and methane in horses.

Abdomen, Acute↗
PubMed1999

Measurement of telomerase activity in dog tumors.

Telomeres are specific structures present at the end of liner chromosomes. DNA polymerase can not synthesize the end of liner DNA and, as a result, the telomeres become progressively shortened by successive cell divisions. To overcome the end replication problem, telomerase adds new telomeric sequences to the end of chromosomal DNA. The enzyme activity is undetectable in most normal human adult somatic cells, in which shortening of the telomere is thought to limit the somatic-cell life span. In contrast to normal somatic cells, many human tumors possess telomerase activity. The present study looked at whether telomerase activity might serve as a marker for canine tumors. Telomerase activity was measured using the telomeric repeat amplification protocol assay. Normal dog somatic tissues showed little or no telomerase activity, while normal testis exhibited a high level of telomerase activity. We measured telomerase activity in tumor samples from 45 dogs; 21 mammary gland tumors, 16 tumors developed in the skin and oral cavity, 7 vascular tumors and 1 Sertoli cell tumor. Greater than 95% of the tumor samples contained telomerase activity (3-924 U/2 micrograms protein). The results obtained in this study indicated that telomerase should be a useful diagnostic marker for a variety of dog tumors, and it may serve as a target for antitumor chemotherapy.

Adenocarcinoma↗