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Biomedical subjects

S Miwa

Publications and source records attributed to S Miwa.

At least 199 records · Page 11Linked to original sources
PubMed1990

Effects of choline administration on in vivo release and biosynthesis of acetylcholine in the rat striatum as studied by in vivo brain microdialysis.

The purpose of the present study is to clarify the effects of the administration of choline on the in vivo release and biosynthesis of acetylcholine (ACh) in the brain. For this purpose, the changes in the extracellular concentration of choline and ACh in the rat striatum following intracerebroventricular administration of choline were determined using brain microdialysis. We also determined changes in the tissue content of choline and ACh. When the striatum was dialyzed with Ringer solution containing 10 microM physostigmine, ACh levels in dialysates rapidly and dose dependently increased following administration of various doses of choline and reached a maximum within 20 min. In contrast, choline levels in dialysates increased after a lag period of 20 min following the administration. When the striatum was dialyzed with physostigmine-free Ringer solution, ACh could not be detected in dialysates both before and even after choline administration. After addition of hemicholinium-3 to the perfusion fluid, the choline-induced increase in ACh levels in dialysates was abolished. Following administration of choline, the tissue content of choline and ACh increased within 20 min. These results suggest that administered choline is rapidly taken up into the intracellular compartment of the cholinergic neurons, where it enhances both the release and the biosynthesis of ACh.

Acetylcholine↗
PubMed1990

Enhancement of in vivo tyrosine hydroxylation in the rat adrenal gland under hypoxic conditions.

We examined the effects of hypoxia (8% O2) on in vivo tyrosine hydroxylation, a rate-limiting step for catecholamine synthesis, in the rat adrenal gland. The hydroxylation rate was determined by measuring the rate of accumulation of 3,4-dihydroxyphenylalanine (DOPA) after decarboxylase inhibition. One hour after hypoxic exposure, DOPA accumulation decreased to 60% of control values, but within 2 h it doubled. At 2 h, the apparent Km values for tyrosine and for biopterin cofactor of tyrosine hydroxylase (TH) in the soluble fraction were unchanged, whereas the Vmax value increased by 30%. The content of total or reduced biopterin was unchanged, but the content of tyrosine increased by 80%. Tyrosine administration had little effect on DOPA accumulation under room air conditions but enhanced DOPA accumulation under hypoxia. After denervation of the adrenal gland, the hypoxia-induced increase in DOPA accumulation and in the Vmax value was abolished, whereas the hypoxia-induced increase in tyrosine content was persistent. These results suggest that in vivo tyrosine hydroxylation is enhanced under hypoxia, although availability of oxygen is reduced. The enhancement is the result of both an increase in tyrosine content coupled with increased sensitivity of TH to changes in tyrosine tissue content and of an increase in dependence of TH on tyrosine levels. The increase in the sensitivity of TH and in the Vmax value is neurally induced, whereas the increase in tyrosine content is regulated by a different mechanism.

Adrenal Glands↗
PubMed1990

Enhancement of dopamine release in vivo from the rat striatum by dialytic perfusion of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin.

We have previously reported that intracerebroventricular administration of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (6R-BH4), a cofactor for tyrosine hydroxylase, enhances biosynthesis of 3,4-dihydroxyphenylethylamine (dopamine) in the rat brain. In the present study, we have more precisely examined the effects of 6R-BH4 on dopamine release in vivo from the rat striatum using brain microdialysis. The amount of dopamine collected in striatal dialysates was determined using HPLC with electrochemical detection after purification with an alumina batch method. When the striatum was dialyzed with Ringer solution containing various concentrations of 6R-BH4 (0.25, 0.5, and 1.0 mM), dopamine levels in striatal dialysates increased in a concentration-dependent manner. Biopterin had little effect on dopamine levels in dialysates. The 6R-BH4-induced increase in dopamine levels in dialysates was abolished after pretreatment with tetrodotoxin (50 microM) added to the perfusion fluid, but after pretreatment with nomifensine (100 mg/kg, intraperitoneal injection), an inhibitor of dopamine uptake mechanism, a larger increase was observed. After inhibition of tyrosine hydroxylase by pretreatment with alpha-methyl-p-tyrosine (250 mg/kg, intraperitoneal injection), most of the increase persisted. These results suggest that 6R-BH4 has a dopamine-releasing action, which is not dependent on biosynthesis of dopamine.

Animals↗
PubMed1990

Effects of hypoxia on the catecholamine release, Ca2+ uptake, and cytosolic free Ca2+ concentration in cultured bovine adrenal chromaffin cells.

The purpose of the present study is to clarify the effects of hypoxia on catecholamine release and its mechanism of action. For this purpose, using cultured bovine adrenal chromaffin cells, we examined the effects of hypoxia on high (55 mM) K(+)-induced increases in catecholamine release, in cytosolic free Ca2+ concentration ([Ca2+]i), and in 45Ca2+ uptake. Experiments were carried out in media preequilibrated with a gas mixture of either 21% O2/79% N2 (control) or 100% N2 (hypoxia). High K(+)-induced catecholamine release was inhibited by hypoxia to approximately 40% of the control value, but on reoxygenation the release returned to control levels. Hypoxia had little effect on ATP concentrations in the cells. In the hypoxic medium, [Ca2+]i (measured using fura-2) gradually increased and reached a plateau of approximately 1.0 microM at 30 min, whereas the level was constant in the control medium (approximately 200 nM). High K(+)-induced increases in [Ca2+]i were inhibited by hypoxia to approximately 30% of the control value. In the cells permeabilized by digitonin, catecholamine release induced by Ca2+ was unaffected by hypoxia. Hypoxia had little effect on basal 45Ca2+ uptake into the cells, but high K(+)-induced 45Ca2+ uptake was inhibited by hypoxia. These results suggest that hypoxia inhibits high K(+)-induced catecholamine release and that this inhibition is mainly the result of the inhibition of high K(+)-induced increases in [Ca2+]i subsequent to the inhibition of Ca2+ influx through voltage-dependent Ca2+ channels.

Adenosine Triphosphate↗
PubMed1990

Pyruvate kinase deficiency.

PK deficiency is the most common and well characterized erythroenzymopathy in the Embden-Meyerhof glycolytic pathway associated with hereditary hemolytic anemia. History of discovery, clinical features, biochemical studies, as well as recent studies on molecular level were reviewed, with a stress on our own studies. As reference materials, Tables 2 and 3 are attached.

Anemia, Hemolytic↗
PubMed1990

[A Japanese family with hereditary HbH disease--a case report and its gene analysis].

Hereditary HbH disease was found in a Japanese family. The propositus showed hypochromic microcytic anemia and chronic hemolysis. HbH inclusion bodies were detected in red cells, and an abnormal band corresponding HbH was found in an isoelectric focusing of the hemolysate. Gene analysis of the propositus revealed double heterozygosity for alpha + and alpha zero thalassemias. Four of six his siblings shared the alpha zero thalassemia and one the alpha + thalassemia. Another one was normal. The alpha + thalassemia was of 3.7 kb-deletion type and alpha zero was close to Southeast Asian type. This is the fourth Japanese family with hereditary HbH disease.

Adult↗
PubMed1989

Human adenylate kinase deficiency associated with hemolytic anemia. A single base substitution affecting solubility and catalytic activity of the cytosolic adenylate kinase.

Adenylate kinase deficiency in the erythrocyte is a rare genetic disorder associated with hemolytic anemia. To determine the molecular basis of this disorder, we first cloned the normal gene encoding human cytosolic adenylate kinase (AK1) and determined the structure. The gene was 12 kilobase pairs long and was split into 7 exons. The structures of 5'- and 3'-flanking regions were determined by primer extension and RNA blot analysis. The results showed that two species of mRNA with 0.9 and 2.5 kilobases, which differed at the 3'-end portion, were generated by the AK1 gene. Alu sequences were found in the largest intron (intron 5) and in the noncoding region of exon 7. Next, both alleles of the AK1 gene were cloned from DNA of a patient bearing the adenylate kinase deficiency and their nucleotide sequences determined. A transition (C----T) was found in exon 6 on an allele, which resulted in an Arg to Trp (CGG----TGG) substitution at the 128th residue of AK1. Since chicken AK1 is highly homologous to human AK1 with respect to the amino acid sequence, we introduced an Arg to Trp substitution to chicken AK1 at the same position by oligodeoxynucleotide-directed mutagenesis. The mutant chicken AK1 expressed in Escherichia coli showed a reduced catalytic activity as well as a decreased solubility and a change in affinity to phosphocellulose. Thus it was considered that the observed C----T transition was a cause of the decreased AK1 activity of the patient's erythrocyte. Analysis on phosphocellulose chromatography of erythrocyte AK1 of the patient and parents revealed that the patient's mutant allele was derived from the mother.

Adenylate Kinase↗
PubMed1989

Erythrocyte enzyme activities in myelodysplastic syndromes: elevated pyruvate kinase activity.

The erythrocyte enzyme activities in twenty-six cases of myelodysplastic syndromes were determined. There were remarkably abnormal levels in seven cases; namely, four cases showed increased hexokinase activity, three cases showed increased pyruvate kinase activity, and two cases showed increased adenosine deaminase activity. Among these, one case with elevated pyruvate kinase activity showed the novel expression of M2-type pyruvate kinase activity, in addition to the R-type pyruvate kinase activity normally found in erythrocytes. Southern blotting of peripheral leucocyte DNA revealed only an amplified PK-LR genome, which derived from the chromosomal abnormality of a 1;7 translocation. The mechanism responsible for switching M2-type to R-type during erythroid maturation was considered to be partially disrupted in this case.

Blotting, Southern↗
PubMed1989

Effects of hypoxia on noradrenaline release and neuronal reuptake in isolated rabbit thoracic aortic strips.

To clarify the effects of hypoxia on stimulus-evoked noradrenaline release and on neuronal reuptake of the released noradrenaline, we examined the effects of hypoxia on contraction responses of rabbit thoracic aortic strips to transmural electrical stimulation and on the stimulation-evoked overflow of total [3H] and [3H]noradrenaline from the strips prelabelled with [3H]noradrenaline. This was done in the presence or absence of an inhibitor of neuronal uptake (cocaine). In a medium equilibrated with a gas mixture of 95% O2/5% CO2 (control), cocaine doubled the stimulation-evoked overflow of total [3H] and [3H]noradrenaline; there was a concomitant increase (130%) in contractions to electrical stimulation. At 0% O2 (95% N2/5% CO2, hypoxia), cocaine had no significant effects on either the stimulation-evoked overflow of total [3H] and [3H]noradrenaline or contractions. In the absence of the drug, hypoxia decreased the stimulation-evoked overflow of total [3H] and [3H]noradrenaline to 47% and 43%, respectively, of the control values, whereas these values were 31% and 28%, respectively, after exposure to cocaine. The inhibition by hypoxia of contraction responses to electrical stimulation was greater in the presence of cocaine than in its absence. These results show that hypoxia inhibits both noradrenaline release evoked by a given stimulus and neuronal uptake.

Animals↗
PubMed1989

Effects of bovine TSH on the tissue thyroxine level and metamorphosis in prometamorphic flounder larvae.

Bovine thyroid-stimulating hormone (TSH) was microinjected (0.2 microliter/fish) into prometamorphic flounder larvae and the effects on metamorphosis as well as the tissue thyroxine (T4) and triiodothyronine (T3) levels were studied. After a single injection of TSH (5 mIU/g), the tissue T4 concentration increased markedly after 5 hr, reached a peak after 10 hr, and decreased subsequently. T4 concentration after 24 hr was still higher than in saline-injected fish but returned to the control level 48 hr after the injection. On the other hand, tissue T3 concentration was kept lower than the detectable level (0.2 ng/g) throughout the experimental period of 72 hr after a single injection of TSH (5 mIU/g). TSH treatment also accelerated the process of metamorphic climax, such as shortening of the second fin ray and eye migration. These results suggest that an increased secretion of TSH from the pituitary stimulates the thyroid, resulting in a surge of the tissue T4 concentration which induces the climax of the flounder larvae.

Aging↗
PubMed1989

Determinants of late potentials in myocardial infarction.

To clarify factors which have an influence on late potentials (LPs), signal averaged electrocardiogram, echocardiogram, cardiac catheterization and Holter monitoring were studied in 86 patients with previous myocardial infarction (MI). Group 1 consisted of 27 patients with LPs (LP duration greater than or equal to 20 msec) and Group 2 consisted of 59 patients without them. Twelve percent of anterior MI and 35% of inferior MI had LPs. Left ventricular (LV) diastolic dimension was larger and % fractional shortening was lower in group 1 than those in group 2. LV end-diastolic volume index and LV end-systolic volume index were larger and LV ejection fraction was lower in group 1 than those in group 2. Aneurysm was noted in 37% in group 1 and 17% in group 2 (p less than 0.05), and mean number of involved coronary vessels was 2.3 +/- 0.8 in group 1 and 1.7 +/- 0.8 in group 2 (p less than 0.05). No significant difference was found in other clinical and hemodynamic parameters. The incidence of patients with 100 or more ventricular premature contractions per hours and that with ventricular tachycardia (VT) were significantly higher in group 1 than in group 2 (26% vs 7%, p less than 0.05, 33% vs 7%, p less than 0.01, respectively). Multiple regression analysis and the method of quantification demonstrated that ventricular arrhythmia was most strongly associated with LP duration.

Action Potentials↗
PubMed1989

The effects of class IA antiarrhythmic drug on the common type of atrial flutter in combination with pacing therapy.

In 11 patients with common type of atrial flutter (common AF), rapid atrial pacing from the high right atrium was performed before and/or after class Ia antiarrhythmic drug administration, confirming transient entrainment by decreasing the pacing cycle length by 10 ms. In 10 patients before the drug administration, common AF was not interrupted although the pacing cycle length was decreased to 200 ms in 5 patients, accelerated atrial flutter or atrial fibrillation was induced in 4 patients, and common AF was converted into sinus rhythm in only 1 patient. After the drug administration common AF was converted into sinus rhythm in 5 out of 6 patients. The class Ia antiarrhythmic drug prolonged the common AF cycle length (255 +/- 12 ms vs. 298 +/- 37 ms, p less than 0.005) and widened the entrainment zone (64 +/- 7 ms vs. 90 +/- 20 ms, p less than 0.05). The widening of the entrainment zone and the prolongation of the common AF cycle length facilitate the successful conversion of common AF at a longer pacing cycle length, which would not precipitate atrial fibrillation or accelerated atrial flutter. The combination therapy of rapid atrial pacing and the class Ia antiarrhythmic drug is thought to be useful in the therapy of common AF.

Adult↗
PubMed1989

Molecular basis of red cell enzymopathies associated with hereditary nonspherocytic hemolytic anemia.

In the past few years, very rapid advances have been made in the field of red cell enzymopathies associated with hereditary nonspherocytic hemolytic anemia, particularly in molecular basis. Nucleotide sequence and amino acid sequence of normal human red cell enzymes have been clarified in phosphofructokinase, aldolase, triosephosphate isomerase, phosphoglycerate kinase, pyruvate kinase, diphosphoglycerate mutase, glucose 6-phosphate dehydrogenase, adenylate kinase and adenosine deaminase. Furthermore, in aldolase-, triosephosphate isomerase-, diphosphoglycerate mutase-, glucose 6-phosphate dehydrogenase-, and adenylate kinase deficiency, single nucleotide changes which cause single amino acid substitutions and finally hemolysis, have been found.

5'-Nucleotidase↗