Search PubMed⌕ Search

Biomedical subjects

M Yokoyama

Publications and source records attributed to M Yokoyama.

At least 19 recordsLinked to original sources
PubMed1992

Involvement of MAP kinase activators in angiotensin II-induced activation of MAP kinases in cultured vascular smooth muscle cells.

In cultured vascular smooth muscle cells (VSMC) angiotensin II (ang II) induces tyrosine and serine/threonine phosphorylation and activation of two mitogen-activated protein (MAP) kinases. When extracts of ang II-stimulated VSMC were fractionated by Mono Q anion-exchange column chromatography, three peaks of the activities which in vitro activate inactive MAP kinases were detected. These MAP kinase activator activities were not detected in extracts of unstimulated VSMC. In vitro activation of MAP kinases by the MAP kinase activators was accompanied by tyrosine and serine/threonine phosphorylation of MAP kinases. These results suggest that the MAP kinase activators are involved in the ang II-induced phosphorylation and activation of MAP kinases in VSMC.

Angiotensin II↗
PubMed1992

Expression of Fos-like immunoreactivity by yohimbine and clonidine in the rat brain.

To elucidate the role of alpha 2-adrenoceptors in transcriptional control in the rat brain, we localized the Fos-like immunoreactivity (Fos-LI) induced by alpha 2-adrenoceptor agonists and by an antagonist. Injections of yohimbine (5 mg/kg, i.p.) into rats led to the induction of Fos-LI in areas with a dense alpha 2-adrenoceptor binding such as the locus coeruleus, the bed nucleus of stria terminalis, the central nucleus of amygdaloid complex, the paraventricular nucleus, the nucleus tractus solitarius, and ventrolateral medulla oblongata. Clonidine (500 micrograms/kg, i.p.) suppressed the Fos expression by yohimbine in these nuclei, and clonidine (100 micrograms/kg, i.p.) or guanabenz (4 mg/kg, i.p.) induced Fos-LI in oxytocin neurons in the paraventricular and supraoptic nuclei in the hypothalamus. Thus, the alpha 2-adrenoceptor is involved in transcriptional control via Fos expression in neurons related to autonomic and other functions.

Animals↗
PubMed1992

Studies on the hepatotoxicity induced by bis (tributyltin) oxide.

The toxic effects of bis (tributyltin) oxide (TBTO) on the rat liver were studied with an electron microscope and the accumulation sites of tin were determined with an X-ray microanalyzer. The activities of serum enzymes and the concentration of serum bilirubin were also analyzed. Male Wistar rats received an intramuscular injection of 0.5 ml/kg of TBTO. Marked swelling of the mitochondria appeared in the hepatocytes 4 h after injection of TBTO. Cytoplasmic vacuoles, which contained degenerated mitochondria, gradually increased in number in these hepatocytes. This in turn may have caused a decrease in the volume of hepatic cell cords and an enlargement of sinusoids in the entire hepatic lobule. However, fine structures of intrahepatic bile ducts were not altered. By X-ray microanalysis, tin peaks were preferentially obtained from swollen mitochondria of the hepatocytes. By polarographic analysis of the respiratory responses of mitochondria, it was demonstrated that rates of state 4 respiration and respiratory control ratio were significantly disturbed in TBTO-treated rats in comparison with those of controls. The activities of AST (aspartate aminotransferase) and ALT (alanine aminotransferase) were significantly increased after TBTO treatment, but those of ALP (alkaline phosphatase), LAP (leucine aminopeptidase) and total bilirubin were not changed. These results indicated that parenterally administered TBTO accumulated in the liver cell mitochondria and disturbed oxidative phosphorylation. Mitochondrial dysfunction might induce severe damage of the hepatocytes. Four days after injection of TBTO, hepatic structures and chemical indices were almost restored by the regeneration of hepatocytes.

Alanine Transaminase↗
PubMed1992

Stimulation of protein-tyrosine phosphorylation by endothelin-1 in cultured vascular smooth muscle cells.

In cultured rat aortic smooth cells, endothelin-1 induced tyrosine phosphorylation of at least five proteins with molecular masses of about 79, 77, 73, 45 and 40 kDa in dose- and time-dependent manners. Platelet-derived growth factor also induced tyrosine phosphorylation of the same set of proteins in addition to other proteins including platelet-derived growth factor receptors. This growth factor markedly stimulated DNA synthesis and an increase in cell number in this cell type, but endothelin-1 failed to stimulate these responses under the same conditions. These results demonstrate for the first time that endothelin-1 induces tyrosine phosphorylation of some proteins but suggest that these reactions are not enough to stimulate proliferation of vascular smooth muscle cells.

Animals↗
PubMed1992

Association of N-glycosylation of apolipoprotein B-100 with plasma cholesterol levels in Watanabe heritable hyperlipidemic rabbits.

We have previously demonstrated the heterogeneity of N-linked sugar chains of apolipoprotein (apo) B-100 in Watanabe heritable hyperlipidemic (WHHL) rabbit and fasting Japanese White rabbits (Arteriosclerosis, 10 (1990) 386-393). To investigate further the role of N-linked sugar chains of apo B-100 in lipid metabolism, we examined the correlation between the N-glycosylation of apo B-100 and serum cholesterol levels in WHHL rabbits. The N-linked sugar chains of apo B-100 were liberated by hydrazinolysis, followed by NaB3H4 reduction and were fractionated by paper electrophoresis and BioGel P-4 column chromatography. These were found to consist of one neutral (N) and two acidic fractions (A1 and A2). N contained a high mannose type oligosaccharide consisting of Man5.GlcNAc2 to Man9.GlcNAc2, while A1 and A2 contained monosialylated and disialylated complex type oligosaccharides, respectively. The molar ratio varied among the 5 WHHL rabbits. There was an inverse correlation between the ratio of acidic oligosaccharide fractions (A1 + A2) and serum cholesterol levels (r = -0.971, P less than 0.01) in the 5 WHHL rabbits. These results indicate that the N-glycosylation of apo B-100 is closely related to cholesterol metabolism in WHHL rabbits.

Animals↗
PubMed1992

The role of the rat submandibular gland in the excretion of bis (tributyltin) oxide: electron microscopy, X-ray microanalysis and atomic absorption analysis.

The role of the submandibular glands in the excretion of parenterally administered bis (tributyltin) oxide (TBTO) was studied. Fine structural alterations of the submandibular glands were observed with an electron microscope. Accumulation sites of TBTO were determined with an X-ray microanalyzer and tin concentrations in saliva and blood were measured by atomic absorption spectrophotometry.

Animals↗
PubMed1992

Detection of human papillomavirus genome and analysis of expression of c-myc and Ha-ras oncogenes in invasive cervical carcinomas.

Invasive carcinomas of the uterine cervix of 38 patients were examined for the presence of human papillomavirus (HPV) genomes and for the state of the c-myc and Ha-ras oncogenes. A combination of Southern blot hybridization and polymerase chain reaction revealed the presence of the genome of HPV type 16 in 17 tumors (45%), that of HPV type 18 in 3 tumors (8%), and that of unknown types in 16 others (42%), while no viral DNA sequences were detected in 2 tumors. Of the 38 tumors, c-myc amplification was found in only 1 tumor, while there was no Ha-ras amplification. Overexpression of the c-myc gene was observed in 15 (44%) of the 34 tumors analyzed, while there was no overexpression of Ha-ras. Of the 23 squamous cell carcinomas analyzed, relapse-free rates at 24 months were 55% in tumors with c-myc overexpression and 100% in case of tumors with no c-myc overexpression, respectively. The results suggest the possibility that activation of the c-myc oncogene is involved in tumor progression.

Base Sequence↗
PubMed1992

Analysis of the human tyrosine hydroxylase promoter-chloramphenicol acetyltransferase chimeric gene expression in transgenic mice.

To investigate cis-elements responsible for catecholaminergic (CAnergic) neuron-specific expression of the tyrosine hydroxylase (TH) gene, we produced lines of transgenic mice carrying 5.0-kb, 2.5-kb and 0.2-kb fragments from the 5'-flanking region of the human TH gene fused to a reporter gene, chloramphenicol acetyltransferase (CAT), and designated them as TC 50, TC 25, and TC 02, respectively, and reporter gene expression in transgenic mice was analyzed by CAT assay by immunocytochemistry with anti-CAT antibody. High-level CAT expression was observed in the brain and adrenal gland using the 5.0-kb promoter of the TC 50 mice, but ectopic expression was consistently observed in several somatic tissues, e.g. thymus, colon, and testis. In brain, expression was achieved in CAnergic neurons with the largest construct (5.0 kb), but not with 2.5 kb or 0.2 kb of 5' flanking sequence. However, TC 50 mice also expressed CAT immunoreactivity in non-CAnergic neurons. In the TC 25 line CAT immunoreactivity was detected only in some non-CAnergic neurons. In the TC 02 line no CAT immunoreactivity was detected in any of the tissues examined. These results indicate that the 5.0-kb DNA fragment of the TH gene upstream region contains activity to express CAT in CAnergic neurons and surprisingly, lacks some regulatory elements attenuating ectopic expression, and that the 2.5-kb and 0.2-kb fragment are not sufficient for the proper expression. We discuss the presence of the tissue-specific regulatory elements in the structure portion of the TH gene and/or 3'-flanking region.

Animals↗
PubMed1992

Biphasic effects of smoking on human serum dopamine-beta-hydroxylase activity.

To investigate the chronic effects of smoking on sympathetic nerve activity, serum dopamine-beta-hydroxylase (DBH) activity was determined in 119 male non-smokers and 183 age-matched male smokers. The smokers were classified into 3 groups: 51 light smokers (1-19 cigarettes/day), 76 moderate smokers (20 cigarettes/day), and 56 heavy smokers (more than 20 cigarettes/day). The light smokers had the highest mean DBH activity, and the heavy smokers had the lowest mean DBH activity in the 4 groups. These results suggest that light smoking stimulates the sympathetic nervous system, but that heavy smoking depresses the system. These biphasic changes in DBH activity are similar to the pharmacological effects of nicotine on the peripheral sympathetic nervous system.

Adult↗
PubMed1992

Regional differences of phospholipase A2 activity in the rabbit oviductal epithelium.

To evaluate the biosynthesis of prostaglandins in the oviducts, phospholipase A2 (EC 3.1.1.4) activities were first measured in the epithelial cells obtained from rabbit oviducts. At least four kinds of phospholipase A2 (PLA2) activities with respect to calcium dependency and pH requirement were observed. There were two calcium-dependent, pH optima of 7.5 and 8.5 activities, and two calcium-independent, pH optima of 4.0 and 8.0 activities. One of those activities, a calcium-dependent and alkaline active PLA2 activity of the epithelial cells was then compared between the ampullary portion and the isthmic portion of the oviducts. The activity was significantly higher in the ampullary epithelium than in the isthmic epithelium (223.2 +/- 57.2 or 103.8 +/- 32.3 pmol/min/mg, p < 0.05). These results support the idea that the production of prostaglandins, which is dependent upon the activity of the arachidonate cascades, was higher in the ampullary portion of oviduct than that in the isthmic portion. The PLA2 activity of the ampullary epithelium may thus play an important role in the regulation of smooth muscle contractility and ciliary movement.

Animals↗
PubMed1992

Blood pressure changes following extracorporeal shock wave lithotripsy for urolithiasis.

Hypertension after extracorporeal shock wave lithotripsy (ESWL) has been a controversial subject. Changes in blood pressure were studied in 262 patients (mean age 47.8 years) 18.6 months after ESWL. According to World Health Organization criteria the number of patients who showed a decrease exceeded those who showed an increase in blood pressure. The patients who have been on antihypertensive therapy showed a significantly greater decrease in blood pressure than those without medication. Of 192 normotensive patients diastolic pressure increased 1.2 mm. Hg and 2 (1.0%) had hypertension 18.4 months after ESWL. Annualized increase in diastolic pressure and new onset of hypertension were calculated to be 0.78 mm. Hg and 0.65%, respectively. Significant elevation of diastolic pressure was noted in the patients who received a larger number of shock waves. Blood pressure should be carefully followed after ESWL especially in patients who have been treated by a greater number of shock waves.

Adult↗
PubMed1992

Determination of left ventricular volume using a conductance catheter in the diseased human heart.

To validate the accuracy of human left ventricular (LV) volume measured by the conductance catheter method, conductance volume was compared with LV volume measured by biplane angiography in 19 patients with ischaemic heart disease. Angiographic LV volumes were calculated frame by frame and matched with instantaneous conductance volumes. Calibration was determined by both gain constant, 1/alpha, and parallel conductance, alpha V c. The gain constant, 1/alpha, was the ratio of stroke volume measured by the thermodilution method to that measured by the conductance catheter. The parallel conductance, alpha Vc, was estimated by the saline injection method. There was a good correlation between the corrected conductance volume (Vcc) and the angiographic volume (V angio) such that Vcc = 0.94 V angio + 5.3 ml, r = 0.94, P < 0.001. There were no differences in the correlation coefficients between normal and depressed hearts. Compared with the angiographic data, LV end-diastolic volume, end-systolic volume and ejection fraction were determined accurately by the conductance catheter. We conclude that the conductance catheter method, corrected for gain constant and parallel conductance, can accurately and continuously estimate the LV volume throughout the cardiac cycle in the diseased human heart.

Aged↗
PubMed1992

Comparison between preload recruitable stroke work and the end-systolic pressure-volume relationship in man.

We compared linearity, inotropic sensitivity (using dobutamine) and afterload dependency (using captopril) of contractile indices derived from the end-systolic pressure-volume relationship (ESPVR) and preload recruitable stroke work (PRSW) in man. We investigated 60 patients, 39 with normal (EF > or = 50%, group 1) and 21 with decreased ventricular function (EF < 50%, group 2). Variably loaded P-V loops were constructed by conductance catheters with vena caval occlusions. The slopes of the ESPVR (Emax) and PRSW (Mw) were assessed by linear regression analysis. The correlation coefficients of the ESPVR (r = 0.964) and PRSW (r = 0.976) were both very high, but the Z-value of the ESPVR was lower than for PRSW. During the control period, normalized Emax and Mw were significantly higher in group 1 than group 2 (Emax: 4.6 +/- 2.3 vs 2.8 +/- 0.8 mm Hg ml-1 m-2, Mw: 109 +/- 31 vs 86 +/- 28 10(3) dyn cm-2. After dobutamine, Emax and Mw increased significantly both in group 1 (128% and 124% vs control respectively) and in group 2 (132% and 130% respectively). After captopril, the ESPVR tended to shift to the right with a decrease in afterload; PRSW was unchanged. We conclude that PRSW may be a more linear and reliable index for evaluation of contractility in man.

Administration, Oral↗
PubMed1992

Assessment of myocardial oxygen consumption (Vo2) and systolic pressure-volume area (PVA) in human hearts.

Several studies have recently reported that the relationship between myocardial oxygen consumption per beat (Vo2) and left ventricular (LV) systolic pressure-volume area (PVA), which represents total mechanical energy generated by contraction, is linear and independent of loading conditions in excised, supported, and intact hearts. We assessed the Vo2-PVA relationship in nine patients with heart disease. LV volume and pressure were measured simultaneously by conductance catheter and tip-micromanometer. Vo2 was calculated from the difference between arterial and coronary sinus oxygen content, and coronary sinus blood flow measured by the thermodilution method. We obtained the linear relationship between Vo2 and PVA by dextran infusions (median r = 0.917). The slope of the Vo2-PVA relationship was (1.82 +/- 0.66) x 10(-5) mlO2 mmHg-1 ml-1 and the contractile efficiency, the reciprocal of the slope of the Vo2-PVA relationship, was 40 +/- 13%. The Vo2 intercept, which reflects Vo2 for non-mechanical work, was 0.0284 +/- 0.0286 ml O2 beat-1. These results suggest that PVA is a good predictor of myocardial oxygen consumption and a powerful tool to evaluate the coupling of LV mechanical performance to energy use in human hearts.

Angina Pectoris↗
PubMed1992

Endothelin-1 stimulates tyrosine phosphorylation and the activities of two mitogen-activated protein kinases in cultured vascular smooth muscle cells.

OBJECTIVE: Endothelin-1 (ET-1) has been reported to stimulate the expression of the proto-oncogenes c-fos and c-myc, and to cause DNA synthesis in vascular smooth muscle cells (VSMC). The purpose of this study was to clarify the signalling pathway from ET receptors to the nucleus. DESIGN: Mitogen-activated protein (MAP) kinase, which is activated by various growth factors via phosphorylation of tyrosine and threonine residues, plays important roles as an intermediate in the signalling pathways from growth factor receptors to the ribosomes and nucleus. We examined the effect of ET-1 on the phosphorylation and activation of MAP kinase in cultured VSMC. METHODS: Extracts of ET-1-stimulated VSMC were analysed by one- and two-dimensional gel electrophoresis and anion-exchange column chromatography. Tyrosine-phosphorylated proteins and MAP kinases were detected by immunoblot analyses with anti-phosphotyrosine and anti-MAP kinase antibodies, respectively. The MAP kinase activity was measured using myelin basic protein as a substrate. The MAP kinases were isolated from 32P-labelled VSMC and subjected to phosphoamino acid analysis. RESULTS: ET-1 induced tyrosine phosphorylation of at least five proteins of about 79, 77, 73, 45 and 40 kDa in VSMC. The mobilities of the tyrosine-phosphorylated 45- and 40-kDa proteins were identical with those of the two proteins that were recognized by anti-MAP kinase antibody upon one- and two-dimensional gel electrophoresis. ET-1 stimulated MAP kinase activity in a time-course similar to that of the tyrosine phosphorylation of the 45- and 40-kDa proteins. The ET-1-stimulated MAP kinase activity was resolved almost equally into two peaks upon Mono Q column chromatography (kinase 1 and kinase 2). Kinase 1 and kinase 2 were co-eluted with the tyrosine-phosphorylated 40- and 45-kDa proteins, respectively. The apparent molecular masses of kinase 1 and kinase 2 estimated by MAP kinase assay in polyacrylamide gel were identical with those of tyrosine-phosphorylated 40- and 45-kDa proteins, respectively. Upon phosphoamino acid analysis, ET-1 stimulated phosphorylation of MAP kinases not only on tyrosine but also on threonine residues. CONCLUSIONS: ET-1 induces tyrosine and threonine phosphorylation and the activation of two species of MAP kinases of 40 and 45 kDa in VSMC.

Animals↗
PubMed1992

Impaired vasodilatory response to atrial natriuretic peptide during atherosclerosis progression.

This study was undertaken to examine the alterations in vascular relaxation responsiveness to endothelium-dependent or -independent vasodilators, including atrial natriuretic peptide (ANP) and acetylcholine, in aortas of Watanabe heritable hyperlipidemic (WHHL) rabbits during the progression of the atherosclerotic plaque. WHHL rabbits were divided into two groups according to age: group 1, 6-11 months, and group 2, 12-18 months. The isolated thoracic aortas obtained from both normal (control) and WHHL rabbits were suspended in a bath containing oxygenated Krebs' buffer for recording of isometric force. The endothelium-dependent relaxation evoked by acetylcholine was reduced in group 1 WHHL rabbits and decreased progressively in proportion to the degree of atherosclerosis progression when compared with age-matched control rabbits. ANP-induced relaxation was not significantly decreased in group 1 WHHL rabbits. However, ANP-induced relaxation was markedly impaired in group 2 WHHL rabbits. Thoracic aortas with severe atherosclerosis were less sensitive to ANP, with a significant increase in the median effective dose, although maximum relaxation induced by ANP was not reduced. Accumulation of cyclic GMP induced by ANP and acetylcholine was markedly reduced in atherosclerotic arteries obtained from group 2 WHHL rabbits compared with control rabbits. Vascular relaxation elicited by nitroglycerin or isoproterenol was not significantly impaired in atherosclerotic arteries from either group 1 or group 2 WHHL rabbits. From these results, we suggest that ANP-induced cyclic GMP formation and vascular relaxation via particulate guanylate cyclase in vascular smooth muscle cells are impaired in severely atherosclerotic arteries.

Acetylcholine↗