PubMed Health⌕ Search

Biomedical subjects

K Tsunekawa

Publications and source records attributed to K Tsunekawa.

At least 19 recordsLinked to original sources
PubMed2005

Spin-torque diode effect in magnetic tunnel junctions.

There is currently much interest in the development of 'spintronic' devices, in which harnessing the spins of electrons (rather than just their charges) is anticipated to provide new functionalities that go beyond those possible with conventional electronic devices. One widely studied example of an effect that has its roots in the electron's spin degree of freedom is the torque exerted by a spin-polarized electric current on the spin moment of a nanometre-scale magnet. This torque causes the magnetic moment to rotate at potentially useful frequencies. Here we report a very different phenomenon that is also based on the interplay between spin dynamics and spin-dependent transport, and which arises from unusual diode behaviour. We show that the application of a small radio-frequency alternating current to a nanometre-scale magnetic tunnel junction can generate a measurable direct-current (d.c.) voltage across the device when the frequency is resonant with the spin oscillations that arise from the spin-torque effect: at resonance (which can be tuned by an external magnetic field), the structure exhibits different resistance states depending on the direction of the current. This behaviour is markedly different from that of a conventional semiconductor diode, and could form the basis of a nanometre-scale radio-frequency detector in telecommunication circuits.

Journal Article↗
PubMed1993

[Efficacy of FEM (5-fluorouracil, epirubicin, mitomycin C) therapy for resected advanced gastric cancer. Ehime Gastric Cancer Study Meeting].

Between April 1990 and March 1991, postoperative adjuvant chemotherapy for resected gastric cancer employing 5-fluorouracil, epirubicin and mitomycin C (FEM) was performed. Forty-two patients subjected to the therapy were considered to have positive serosal invasion and underwent curative operation. FEM therapy consisted of intraoperative intraperitoneal administration of mitomycin C (0.3-0.4 mg/kg) combined with 8 cycles of intravenous bolus injection of epirubicin (20 mg/body) every 2-3 weeks which was started 2 weeks after the operation. Daily oral administration of 5-fluorouracil (150-200 mg/body) was started 2 weeks after the operation and continued for more than 6 months. Thirty-four of the 42 cases were assessable. Major adverse effects were nausea, vomiting, and general fatigue. There were no cardiovascular symptoms. The cumulative two-year survival rate was 74.2%, and follow-up was still under way at this writing.

Aged↗
PubMed1992

[The effect of prostacyclin (PGI) on denervated tissues--especially, about denervation supersensitivity].

It is well known that contractive agents of smooth muscle have denervation supersensitivity. But, the existence of denervation supersensitivity in relaxed ones does not become so clear. We investigated these supersensitivity, especially prostacyclin (PGI2). We made the denervated artery by lumbar sympathetic ganglionectomy in mongrel dogs. Namely, saphenous and dorsal pedal arteries were denervated by this ganglionectomy. And we studied the changes of these arterial tensions by magnus apparatus. Dose-response (D-R) curves of denervated arteries for KCl and noradrenaline (NE) shifted to left against control arteries. Next, we studied effects of PGI2. At first, we measured ED50 of KCl and NE contraction. And, we produced the half contraction on each artery by using ED50 of KCl and NE. Lastly, PGI2 was added on the half contractive arteries to study relaxed changes. D-R curves of denervated arteries for PGI2 shifted to left, too. These denervated arteries acquired the supersensitivity for PGI2. Clinically, if we use relaxants after organ transplantation, these drugs may be very effective for the perfusion of the grafts.

Animals↗
PubMed1991

Participation of the parasympathetic nervous system in the development of activity-stress ulcers.

The present study investigates the effects of truncal vagotomy and drug treatment, comprising atropine methylbromide and chlorisondamine, on the development of activity-stress ulcers in rats. To induce gastric lesions, female rats were housed individually in activity-wheel cages and subjected to a food-restricted schedule of only 1 hr food availability per day. Bilateral truncal vagotomy significantly prevented gastric ulceration, while those rats with vagotomy showed more running activity than sham-operated rats. Daily treatment with either methylatropine (3 and 6 mg/kg, s.c.) or chlorisondamine (2 and 4 mg/kg, i.p.) also significantly decreased the severity of lesions without a significant reduction in running activity. This evidence suggests that the development of activity-stress ulcers is mainly due to the hyperactivity of the peripheral parasympathetic nervous system.

Animals↗
PubMed1991

Afferent innervation of the gallbladder in the cat, studied by the horseradish peroxidase method.

Following injection of horseradish peroxidase (HRP) into the wall of the gallbladder of cats, HRP-positive cells were found bilaterally in dorsal root ganglia T2-L3 (T2-L2, and T3-L2/L3 also observed in a few cats) and nodose ganglia. In about 33% of animals labelled cells were also distributed in cervical dorsal root ganglia C5-C7. Labelled cells were more frequently localized on the right side than the left. There was no apparent change in numbers of labelled cells in the nodose ganglion (NG) on either side following greater and lesser splanchnicotomy or section of the right phrenic nerve or removal of the celiac ganglion. After severing both the greater and lesser splanchnic nerves unilaterally, numbers of labelled afferent cells from the gallbladder in dorsal root ganglia (DRGs) significantly decreased on the ipsilateral side but there was no change in the pattern of distribution contralaterally. After section of the right phrenic nerve, labelled cells were not found in ipsilateral cervical ganglia. That some afferent fibers from the gallbladder travel via the phrenic nerves, particularly on the right side, may be a supplementary mechanism in the generation of referred pain in gallbladder disease. The splanchnic nerves are the main, but not the only pathway for afferent fibers from the gallbladder.

Afferent Pathways↗
PubMed1991

Polymorphisms of serum proteins in Japanese patients with vascular diseases. I. Factor XIIIB, plasminogen and complement types in primary varicose veins.

The polymorphisms of the B subunit of coagulation factor XIII (F13B), plasminogen (PLG), complement C6, C7, factor B (BF) and factor I (IF) were studied among 21 unrelated Japanese patients with primary varicose veins (PVV) by isoelectric focusing followed by immunoblotting. The allele frequencies for F13B*2 and IF*A in PVV patients were significantly higher (F13B*2, p = 0.0047; IF*A, p = 0.0006) than those in healthy controls (n = 60). Significant associations of F13B 2 allotype [p = 0.0220, relative risk (RR) = 13.9] and IF A allotype (p = 0.0006, RR = 10.0) with PVV were observed; however, no significant association of PLG, C6, C7 or BF allotype with the disease was found.

Adult↗
PubMed1990

Deformation response of red blood cells in oscillatory shear flow.

The characteristics of red cell deformation were studied, focusing on deformation response of the cells subjected to oscillatory shear stress. Red blood cells were fractionated into subpopulations of different densities, i.e., low-density and high-density cells. The deformation response of the fractionated cells was evaluated with a rheoscope varying their intracellular viscosity and oscillation frequency of the applied shear stress, and determinants of the deformation response were compared with those of whole cell deformation under stationary shear stress. When the fractionated cells were exposed to sinusoidally oscillated shear stress, the cells underwent oscillatory deformation. The degree of deformation of the low-density cells correspond to the magnitude of the applied shear stress up to an oscillation frequency of 2.7 Hz. Meanwhile, such an oscillatory deformation as to correspond to the applied shear stress was observed up to 1.7 Hz for the high-density cells. It was suggested that intracellular viscosity was an important factor to determine the deformation response of red cells to oscillatory shear stress.

Cell Survival↗
PubMed1990

Sympathetic supply to the arteries of canine hindlimbs.

Sympathetic supply to the saphenous and dorsal pedal arteries of canine hindlimbs was determined using the glyoxylic acid method for monoamines for the fluorescence histochemical demonstration. Adrenergic nerve fibers of the dorsal pedal artery had almost completely disappeared after L6, L7 sympathectomy. The fibers of the saphenous artery had disappeared by about 90% by L3-L5 sympathectomy. It is concluded that all the postganglionic fibers distributed to the dorsal pedal artery originate in L6 and L7 ganglia and 90% of those distributed to the saphenous artery originate in L3-L5 ganglia.

Animals↗
PubMed1990

Drug interaction between phenytoin and allopurinol.

The combination of phenytoin (DPH) and allopurinol is used for the treatment of a neurological disease. However, interactions between DHP and allopurinol and the mechanism are little known. The repeated dosing of allopurinol at higher doses (20 and 50 mg/kg) significantly retarded the elimination of DPH from the circulation and dramatically decreased the urinary excretion of p-hydroxyphenytoin (HPPH), a major metabolite of DPH. However, a single administration of allopurinol (10 or 50 mg/kg) did not give rise to these effects. Allopurinol did not affect the hepatic extraction of DPH and renal plasma flow rate. Allopurinol (50 mg/kg/d) dosed repeatedly could not inhibit the hepatic drug metabolizing enzyme activities. The in vitro hydroxylation of DPH was inhibited only slightly and the kinetic plots gave apparently non-competitive inhibition. The less inhibitory effect of allopurinol on the in vitro hydroxylation did not agree with the in vivo data. These results indicate that the inhibitory effect of allopurinol is not mediated by cytochrome P-450 dependent monooxygenase reactions.

Administration, Oral↗
PubMed1990

Regulatory role of enteric mu and kappa opioid receptors in the release of acetylcholine and norepinephrine from guinea pig ileum.

We examined the role of opioid receptor subtypes in the contraction and release of acetylcholine (ACh) and norepinephrine in longitudinal muscle-myenteric plexus preparations of the guinea pig ileum. [D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) (10(-8) to 10(-5) M) inhibited the contraction and the release of ACh evoked by 0.2 and 1 Hz of electrical stimulation (ES), whereas the response to 5 Hz was enhanced by low concentrations of DAMGO (10(-9) to 10(-8) M) and inhibited by high concentrations (10(-7) to 10(-5) M); naloxone antagonized these effects. In preparations treated with yohimbine, DAMGO inhibited the ES (5 Hz)-evoked contraction and ACh release, but failed to enhance either effect. Dynorphin-A inhibited the contraction and ACh release evoked by 0.2, 1 and 5 Hz of ES, and the effect of dynorphin-A was mimicked by U-69593 [5 alpha,7 alpha,8 beta-(-)-N-methyl-N-[7- (pyrrolinyl)-1-ozaspiro(4,5)dec-8-yl]-benzene] and antagonized by MR 2266 [(-)-alpha-5,9-diethyl-2-(3-furylmethyl)-2'-hydroxy-6,7-benzomorphan]. The release of norepinephrine evoked by 5 Hz of ES was inhibited by DAMGO (10(-10) to 10(-6) M), but not by U-69593, and the effect of DAMGO was antagonized by naloxone. Thus, it would appear that mu-opioid receptors are present on both cholinergic and adrenergic neurons, whereas kappa-opioid receptors are present on cholinergic neurons. The affinity of DAMGO was 30 times higher for the mu-opioid receptors on the adrenergic than on the cholinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1987

[A case of primary intracranial malignant lymphoma associated with gastric carcinoma].

A case of synchronous multiple primary neoplasms, an intracranial malignant lymphoma and a gastric carcinoma, is presented. A 63-year-old man was admitted to our hospital with complaints of dizziness and a floating sensation on gait. A CT scan after admission, revealed a well-defined, nodular high density area in the left frontal lobe, which was markedly enhanced by the contrast medium. In order to rule out a metastatic brain tumor, examinations were performed as a consequence, and, the gastric carcinoma was found. A partial removal of the brain tumor and a gastrectomy were performed in two stages. Pathologically, the diagnosis of the brain tumor indicated a malignant lymphoma of large cell type, and that of the gastric carcinoma was an adenocarcinoma. The patient received postoperative irradiation and chemotherapy and was discharged in a good condition. He died of pneumonia 21 months after the operation. Necropsy revealed a marked atrophy of the brain without recurrence of the malignant lymphoma and no recurrence of a gastric cancer.

Adenocarcinoma↗
PubMed1982

Choriocarcinomatous change with immunocytochemically HCG-positive cells in the gastric carcinoma of the males.

Gastric choriocarcinoma is a rare tumor and attracts interest because of its controversial pathogenesis. The present study reports a choriocarcinomatous change with immunocytochemically hCG-positive cells in the gastric carcinoma. The patients were males, one was 41 years old and the other 42 years old. The tumor of both cases consists of adenocarcinoma and choriocarcinoma. A sequential process of morphological transition of the adenocarcinoma to the choriocarcinoma can be traced. Indirect immunoperoxidase stain (PAP method) for human chorionic gonadotropin (hCG) demonstrates the localization of hCG in the syncytiotrophoblasts. Small number of cytotrophoblasts are weakly positive. None of the components of adenocarcinoma of both cases is positive for hCG. Human placental lactogen is not demonstrated in both cases. Stain for pregnancy specific beta-1 glycoprotein is weakly positive in the adenocarcinoma of one case but not in the choriocarcinoma. In one case, the concentration of hCG was 19.9 mIU/ml in the preoperative serum and decreased to 1.2 mIU/ml after gastrectomy. HCG production by gastric carcinoma was discussed with regard to possible pathogenesis of gastric choriocarcinoma.

Adenocarcinoma↗
PubMed1980

A serious problem of the heated thermocouple flowmeter.

In the measurement of regional blood flow with heated thermocouple flowmeter, we frequently observed puzzling phenomenon that the measured values were augmented while the flow was actually diminished and vice versa (Inversion). "Inversion" was directly attrebutable to the structure of the thermocouple probe. A countermeasure against "Inversion" was found to lie in the arrangement of the hot junction in the center of the heater, and in practical application, it must be checked by stopping the flow at each measurement. Overcoming this technical liability should pave the way for a marked improvement in the reliability of this method which, despite possessing many excellent characteristics for determining regional blood flow, is not widely used.

Animals↗
PubMed1979

Quantitative histological study of spinal afferent innervation on the ventral surface of the cat stomach by horseradish peroxidase (HRP) method.

Retrograde axonal transport of horseradish peroxidase (HRP) was applied to the ventral surface of the cat stomach. We investigated the number, size and distribution of HRP-positive cells in spinal ganglia. The unexpected finding was the wide distribution of these cells from T3 down to L3. This would result in a diffuse pattern of referred pain.

Afferent Pathways↗