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Biomedical subjects

K Okada

Publications and source records attributed to K Okada.

At least 1,009 records · Page 56Linked to original sources
PubMed1991

Endothelin converting enzyme of bovine carotid artery smooth muscles.

This is the first report clearly demonstrating the presence of endothelin (ET) converting enzyme in vascular smooth muscle. Like cultured endothelial cells, noncultured vascular smooth muscle homogenate of bovine carotid arteries, converts human big ET- 1 to ET-1 at pH 3.0, pH 5.0 and pH 7.0, and the apparent ratio of these three activities is about 6:5:1, respectively. Peptides generated during incubation of the homogenate and big ET- 1 at the three pHs were identified as ET- 1 by radioimmunoassay and high performance liquid chromatography. The two acid enzymes are in the cytosol (103,000xg sup) and are inhibited by pepstatin A, while the neutral enzyme is sensitive to EDTA or phosphoramidon; 73% of the neutral enzyme activity was membrane-bound and the remainder (27%) cytosolic.

Animals↗
PubMed1991

Molecular cloning of a cDNA of a camptothecin-resistant human DNA topoisomerase I and identification of mutation sites.

Camptothecin (CPT), a plant alkaloid with antitumor activity, is a specific inhibitor of eukaryotic DNA topoisomerase I. We have previously isolated and characterized a CPT-resistant topoisomerase I isolated from a CPT-resistant human leukemia cell line, CPT-K5. cDNA clones of topoisomerase I were isolated from the CPT-resistant and the parental CPT-sensitive cell lines, respectively. Sequencing of the clones identified two mutations in the cDNA isolated from the resistant cells, which cause amino acid changes from aspartic acid to glycine at residues 533 and 583 of the parental topoisomerase I. When the CPT-K5 topoisomerase I was expressed in E. coli as a fusion protein with Staphylococcal Protein A fragment, the activity was resistant to CPT at a dose level up to 125 microM, whereas the parental fusion protein was sensitive to CPT as low as 1 microM. The resistance index (greater than 125) of the CPT-K5 fusion topoisomerase I is similar to that of the native CPT-K5 topoisomerase I. These results indicate that either or both of the two amino acid changes identified in the mutant enzyme is responsible for the resistance to CPT.

Amino Acid Sequence↗
PubMed1991

Does a gonadotropin-releasing hormone analogue prevent cisplatin-induced spermatogenic impairment? An experimental study in the mouse.

The cytotoxic effect of cis-diamminedichloroplatinum II (cisplatin, CDDP) on spermatogenesis in BALB/C mice, and possible protection of the testes by leuprolide acetate (D-Leu-6 LHRH(1-9)-ethylamide, TAP-144, leuprolide), a synthetic gonadotropin-releasing hormone analogue, were examined. Temporary interruption of the pituitary-gonadal axis by the analogue and amelioration of the gonadal toxicity of cisplatin by reducing the cell division rate in spermatogenesis were expected. The results showed cisplatin to have a cytotoxic effect on spermatogenic cells in BALB/C mice. The administration of leuprolide had no effect on testicular weight or histological findings in the mouse testes. Pretreatment and simultaneous administration of leuprolide did not reduce the damaging effect of cisplatin on the testes in mice. This is at variance with a previously published report.

Animals↗
PubMed1991

Inter-alpha-trypsin inhibitor (ITI): a useful genetic system in paternity testing. Evidence for polymorphic occurrence of ITI*3 and existence of a new allele, ITI*4.

The genetic polymorphism of human inter-alpha-trypsin inhibitor (ITI) has been investigated in sialidase-treated samples by isoelectric focusing on polyacrylamide gels with a pH range 3.5-9.5 followed by passive blotting with enzyme immunoassay. In 400 blood donors from western Japan, 8 simplified band patterns were observed, 6 of which could be explained by the previously described 3 polymorphic alleles, ITI*1, ITI*2, and ITI*3. The others were products of a new and rare fourth allele designated ITI*4, whose expression is also consistent with autosomal codominant inheritance. The frequency of these alleles was 0.440, 0.526, 0.030 and 0.004, respectively. The theoretical exclusion rate for putative fathers in paternity cases was calculated to be 0.228. The ITI system is a useful genetic marker for forensic hemogenetics in Japanese and in Europeans.

Alleles↗
PubMed1991

mRNA expression of topoisomerase II in human tumors and normal tissues.

The cellular levels of topoisomerase II expression were compared between 10 fresh human tumors and normal tissues to predict the selective anticancer effect of its inhibitors such as adriamycin and VP-16. Topoisomerase II expression was observed in 9 of the 10 tumor tissues (90.0 per cent), 3 of which showed extremely high levels, whereas only 5 of the normal tissues (50.0 per cent) expressed any cellular topoisomerase II and the levels were not higher than those seen in the cancer cells. Six of the 9 positive tumors showed a higher level of topoisomerase II expression than the normal tissues, while the other 3 showed the same level. It can be interpreted from these results that topoisomerase II inhibitors could be effective in cancer patients due to the greater level of this enzyme in tumor cells than in normal tissues. Thus, it is suggested that a comparative analysis of topoisomerase II expression between tumors and normal tissues may be useful for predicting the selective cytotoxicity of topoisomerase II inhibitors in clinical practice.

DNA Topoisomerases, Type II↗
PubMed1991

Effect of platelet-activating factor on lipoprotein lipase and blood lipids.

We investigated the effect of platelet-activating factor (PAF) and of the PAF specific antagonist CV-6209 on plasma lipid metabolism, and particularly on post-heparin plasma lipolytic activity in male Wistar rats. Lipoprotein lipase (LPL) activity was enhanced by intravenous injection of PAF before intravenous injection of heparin when the PAF dose was low (0.2 micrograms/kg). PAF activated hepatic triacylglycerol lipase (HTGL) activity dose-dependently. Plasma triacylglycerols (TG) significantly decreased with the activation of LPL and/or HTGL. Plasma total cholesterol (TC) and phospholipid (PL) levels decreased at a low dose of PAF (0.2 micrograms/kg), but increased when higher doses were used. The PAF antagonist CV-6209 partially reversed the PAF induced effects on HTGL, TC and PL.

Animals↗
PubMed1991

Decreased beta-adrenergic receptor density in rat myocardium during hemorrhagic shock.

We investigated alterations in the number and affinity of cardiac beta-adrenergic receptors during hemorrhagic shock. Forty male Wistar rats were divided into two groups: (1) a shock group (n = 20), in which mean arterial blood pressure was decreased to 40-50 mmHg by bleeding and kept constant for 6 h; and (2) a control group (n = 20), which underwent a sham operation. We used (-)[(3)H]dihydroalprenolol for the determination of the number and affinity of beta-adrenergic receptors in myocardial membranes. An additional 25 rats were used for determination of plasma epinephrine and norepinephrine concentrations. Scatchard analysis showed a 20% reduction ( P < 0.05) in beta-adrenergic receptor density in the shock group (70.3 +/- 3.5 fmol.mg(-1) protein) compared to the control group (90.0 +/- 4.8 fmol.mg(-1) protein) but no significant change in the affinity (2.52 +/- 0.06 vs. 2.31 +/- 0.09 nmol. l(-1), control vs. shock). Plasma catecholamine concentrations were increased significantly at 1, 2, 4 and 6 h after the start of hypotension. These data suggest that increased levels of plasma catecholamines in hemorrhagic shock may be correlated a significant loss of beta-adrenergic receptors in rat myocardium.

Journal Article↗
PubMed1991

Effect of ceruletide on plasma monoamine metabolites in the rabbit.

Ceruletide, a cholecystokinin octapeptide-like substance, has been shown to have some effect on tardive dyskinesia. We, too, previously examined the effect of ceruletide on various types of involuntary movement, and found that responders tended to have high plasma homovanillic acid (HVA) levels. It is generally accepted that both central and peripheral sources make a contribution of plasma HVA. In this study, the response of plasma HVA in rabbits to ceruletide was investigated after pretreatment with debrisoquin sulfate, a drug which selectively blocks peripheral HVA production by inhibition of MAO. As a result, 8 and 50 micrograms/kg ceruletide treatment showed a tendency to decrease plasma HVA levels, but showed no significant differences; however, 140 and 200 micrograms/kg ceruletide showed a significant reduction of plasma HVA. These results are important to the understanding of the mechanism of ceruletide's effect on the brain, as well as to predict the effect of ceruletide on involuntary movements.

Animals↗
PubMed1991

Ossification of the cervical ligamentum flavum.

A case of a 61-year-old man with ossification of the cervical ligamentum flavum is reported. The ossification was located on the left side of C3-4. The symptoms improved with laminectomy and resection. Ossification of the ligamentum flavum usually occurs in the lower thoracic spine, and is rare in the cervical region. Including the present one, only eight cases have been reported to our knowledge. The clinical features and pathogenesis are discussed.

Cervical Vertebrae↗
PubMed1991

Complexation of thiomalic acid with mercury (II) and lead (II) under physiological conditions.

The complex formation of thiomalic acid (H3L) with Hg(II) and Pb(II) was investigated under physiological conditions of 37 degrees C and 0.15 mol dm-3 NaCl by potentiometric titrations using glass electrodes. From the analysis of the emf data in the two systems by use of computer program MIQUV it was concluded that the species formed in the two systems are [HgH4L2], [HgH3L]-, [HgH2L2]2-, [HgHL2]3-, [HgHL], [HgL]-, [HgL2]4-, [Hg(OH)L]2-, [Hg(OH)L2]5-, [PbH2L2]2-, [PbH2L]+, [PbHL2]3-, [PbHL], [PbL]-, [Pb(OH)L]2-, and [Pb(OH)2L]3-. The hydrolytic reactions of Hg(II), data on which were used in the analysis of the above system, were also studied by separate potentiometric titrations. Measurements of 13C NMR spectra of [HgL2]4- and [PbL]- and [PbHL2]3- in D2O solutions suggested that the ligand coordinates with both the metal ions through the sulfhydryl group and one of the two carboxylate groups in such a way that the five-membered chelate ring is formed within the complexes.

Binding Sites↗
PubMed1991

Postoperative cellular reaction on surface modified intraocular lenses in living human eyes.

Specular microscopy was performed to evaluate the postoperative cellular reaction on surface modified poly(methyl methacrylate) intraocular lenses (IOLs) (Ioptex Research, Inc., model U370) in 40 eyes of 36 patients who had extracapsular cataract extraction with implantation of the surface modified IOLs. The cellular elements observed were fibroblast-like cells, histiocytes, and giant cells. Gray amorphous depositions, part of which were sometimes recognized as interference fringes or interference colors, formed a layer in the center of the optics. These depositions were probably caused by the adsorption from aqueous humor. In subclinical cases, only a few histiocytes and giant cells were recognized in the optic center and the optic periphery was free of the cells during our observation. Within two months of surgery most of the cells had disappeared. In vivo specular microscopy showed no manufacturing defects on the implanted lenses. Our findings suggest that, although there was a postoperative cellular reaction on the surface modified IOLs, they were biocompatible.

Aged↗
PubMed1991

Plasminogen activator inhibitor in stomach and colorectal carcinomas.

The content of PAI was measured in carcinoma tissues from the stomach and colorectum divided macroscopically into three portions: the central part of the carcinoma, the marginal part of the carcinoma containing some normal mucosa, and the normal mucosa. The PAI-1 antigen was highest in the central part of the carcinoma. On the other hand, no PAI-1 antigen or activity was observed in the normal mucosa. The PAI-1 in the carcinoma tissues showed a nonlytic zone with a molecular weight of 54 kd by reverse fibrin autography, and this 54 kd band reacted with anti-PAI-1 immunoglobulin G (IgG) on an immunoblotted nitrocellulose membrane. The contents of PAI-2 in the carcinoma tissues were not significantly different from those in the normal mucosa of the stomach and colorectum, respectively. In both the stomach and colorectal carcinomas, the highest value of u-PA/total PA (sum of u-PA and t-PA) was observed in the central part of the carcinoma, followed by the marginal part of the carcinoma, and was lowest in the normal mucosa. We conclude that increased levels of PAI-1 in malignant tissue of the stomach and colorectal tract may serve to modulate extracellular proteolysis by u-PA.

Adult↗
PubMed1991

Synthesis of human big endothelin-1 by sequence-specific proteolysis of a fusion protein in Escherichia coli.

Three DNA constructs, pETB-40, 41, and 42, encoding human big endothelin-1 (ET-1) preceded by the specific recognition sequence (Ile-Glu-Gly-Arg) for the activated blood coagulation factor Xa (FXa), fused in frame to the N-terminal portion of beta Gal, were expressed in Escherichia coli. The fusion proteins, pETB-40P, 41P, or 42P, consisted of the 55-, 51-, or 42-aa N-terminal peptide of beta Gal and the 38-aa of big ET-1, and had 1, 0, or 0 Cys residues and 5, 5, or 1 Arg residues in the N-terminal peptide of beta Gal, respectively. Enzymatic cleavage of the purified fusion proteins by FXa or trypsin allowed the recovery of authentic human big ET-1. The rates of conversion of pETB-40P, 41P, and 42P to big ET-1 by FXa digestion were 5.6, 11.2, and 30.0%, respectively. pETB-40P with a deletion of one Cys residue and four Arg residues in the N-terminal part was a better substrate than the other two for FXa or trypsin in the production of big ET-1.

Amino Acid Sequence↗
PubMed1991

Effects of milrinone on pulmonary vasculature in normal dogs and in dogs with pulmonary hypertension.

OBJECTIVE: To study the effects of milrinone on pulmonary vasculature. BACKGROUND: It has been suggested that bipyridines or their derivatives may have a selective pulmonary vasodilation effect. METHODS: Preliminary study: milrinone administration to 12 normal dogs (low dose [bolus 75 micrograms/kg for 5 min followed by a continuous infusion at 0.75 micrograms/kg.min, n = 6]; high dose [bolus 150 micrograms/kg for 5 min followed by continuous infusion at 1.5 micrograms/kg.min, n = 6]). Main study: milrinone administration to 18 dogs with pulmonary hypertension due to pulmonary embolism induced by a massive injection of autologous muscle cubes. The pulmonary hypertension dogs were divided into three groups: a) group E (n = 6) received embolization only, as control; b) group L (n = 6) received low-dose milrinone; and c) group H (n = 6) received high-dose milrinone, equivalent to the preliminary study group. Hemodynamic measurements and blood samplings were obtained at baseline and at 15, 30, and 60 min after start of milrinone infusion. RESULTS: Milrinone did not change mean pulmonary artery pressure (MPAP) in normal dogs. Milrinone decreased MPAP significantly in dogs with pulmonary hypertension. Pulmonary vascular resistance index remained at an almost constant level in normal dogs, but decreased significantly in dogs with pulmonary hypertension. Mean arterial pressure was maintained at a constant level in all groups. High-dose milrinone administration decreased systemic vascular resistance index (SVRI) significantly; low-dose milrinone administration decreased SVRI slightly. CONCLUSIONS: Milrinone may have a selective pulmonary vasodilatory effect only in dogs with pulmonary hypertension. The mechanism that produced a selectivity on pulmonary vasculature in dogs with pulmonary hypertension is unknown. However, an inhibition of platelet aggregation may decrease the MPAP resulting from an increase in cAMP caused by milrinone. Further studies are needed to resolve the pulmonary vasodilatory effect of milrinone in dogs with pulmonary hypertension.

Animals↗
PubMed1991

Endothelin-converting enzyme and its in vitro and in vivo inhibition.

We investigated endothelin (ET)-converting enzyme and its localization in the vasculature. The membrane and cytosol fractions of cultured endothelial cells of bovine carotid artery contain phosphoramidon-sensitive ET-converting enzymes, and their molecular weights are about 100 and 540 kDa, respectively. The specific conversion of big ET-1 by these enzymes proceeds at pH 7.0 +/- 0.5, and it is inhibited by EDTA, o-phenanthroline, and phosphoramidon. Big ET-3 is converted by the membrane enzyme at a rate about one-tenth that of big ET-1, but it is not converted by the cytosol enzyme. Big ET-1 (but not ET-1)-induced hypertension in rats was remarkably suppressed by pretreatment with phosphoramidon, and big ET-1 (but not ET-1)-induced contraction of isolated coronary arteries, either with or without the endothelium, was substantially suppressed by phosphoramidon. These results suggest an essential role of phosphoramidon-sensitive enzyme(s) in the vascular conversion of big ET-1, and the existence of such enzymes also in nonendothelial cells. We found three converting enzymes operating at different optimal pH values in noncultured vascular smooth muscle cells; two pepstatin-sensitive, cytosolic acid proteinases and a phosphoramidon-sensitive neutral enzyme(s) in the membrane and cytosol. All of these findings strongly suggest the importance of phosphoramidon-sensitive neutral enzymes in the vascular conversion of big ET-1.

Animals↗
PubMed1991

Interaction between endothelin-induced Na+ and Ca2+ kinetics in cultured rat vascular smooth muscle cells.

The present study was undertaken to examine the interaction between endothelin-1 (ET-1)-induced Ca2+ and Na+ kinetics in cultured rat vascular smooth muscle cells (VSMCs) by measuring cytosolic free Ca2+ ([Ca2+]i) and intracellular Na+ ([Na+]i) using intracellular fluorescent dyes (fura-2 and SBFI, respectively). ET-1 increased both [Ca2+]i (basal, 58.9 nM; 10(-9) M, 119.8 nM; 10(-8) M, 265.0 nM; 10(-7) M, 419.0 nM) and [Na+]i (basal, 13.4 mM; 10(-9) M, 17.1 mM; 10(-8) M, 21.6 mM; 10(-7) M, 25.2 mM) in a dose-dependent manner in cultured rat VSMCs. The Na(+)-free solution enhanced the 10(-7) M ET-1-mobilized [Ca2+]i (419 vs. 1,192 nM) but reduced the 10(-7) M ET-1-induced increase in [Na+]i (25.2 vs. 6.1 mM). The Ca(2+)-free solution decreased the peak levels of 10(-7) M ET-1-induced mobilization of [Ca2+]i (411 vs. 350 nM) and the sustained increase in [Ca2+]i and totally diminished the 10(-7) M ET-1-induced increase in [Na+]i (25.2 vs. 12.8 mM). These results therefore indicate that ET-1 increases [Na+]i in association with an increase in cellular Na+ and Ca2+ uptake in VSMCs.

Animals↗