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Biomedical subjects

K Yokoya

Publications and source records attributed to K Yokoya.

14 recordsLinked to original sources
PubMed2003

Oryzalin-induced chromosome doubling in Rosa and its effect on plant morphology and pollen viability.

Shoot tips of the diploid rose Thérèse Bugnet were treated in vitro to oryzalin at concentrations of 5 and 15 microM. Tetraploid shoots were obtained in highest frequencies (40%) after exposure to 5 microM oryzalin for 14 days. Thin (1 mm) nodal sections were treated with 5 microM oryzalin and the highest frequency of tetraploids (66%) was obtained after exposure for only 1 day. The shorter exposure times required to induce chromosome doubling in thin nodal sections is attributed to the more efficient delivery of oryzalin to the meristem. Tetraploids were obtained from four diploid roses and hexaploids from two triploid roses. Chromosome doubling was accompanied by increases in thickness and a darker green colouration of the leaves and, in all diploid to tetraploid and one triploid to hexaploid conversion, the breadth/length ratio of leaflets was significantly increased. Internodes were longer in tetraploids than diploids but significantly shorter in hexaploids than triploids. The number of petals per flower in the tetraploid form of Thérèse Bugnet was double that of the diploid. Significant increases in pollen viability accompanied chromosome doubling of all four diploids and one of the two triploids.

Cell Division↗
PubMed2000

Considerable time from the onset of plaque rupture and/or thrombi until the onset of acute myocardial infarction in humans: coronary angiographic findings within 1 week before the onset of infarction.

BACKGROUND: It has been thought that the thrombi and bleeding in plaques that occur after plaque rupture or endothelial damage from vessels with mild stenosis suddenly occlude the lumen and cause acute myocardial infarction (AMI). However, our hypothesis is that thrombi and bleeding may not suddenly occlude the lumen. METHODS AND RESULTS: The study group consisted of 20 patients who had coronary angiograms performed within 1 week (3+/-3 days) before AMI and 20 control patients who had coronary angiograms performed 6 to 18 months (282+/-49 days) before AMI. The features of infarct-related coronary segments (IRCS) at 3 days before AMI were the presence of a significant stenosis of >50% (95% in incidence and 71+/-12% diameter stenosis) and Ambrose's type II eccentric lesions (plus multiple irregularities), an indicator of plaque rupture and/or thrombi (60% [70%]), and the features at 1 year before AMI were mild stenosis of <50% (95% incidence and 30+/-18% diameter stenosis) with rare Ambrose's type II eccentric lesions (plus multiple irregularities) (10% [10%]). The same relation was observed in each of the 4 subgroups with Q-wave infarction, non-Q-wave infarction, preceding effort angina within 1 month before AMI, and no preceding effort angina. CONCLUSIONS: The appearance of marked progression and Ambrose's type II eccentric lesion on coronary angiograms 3 days before AMI suggests the presence of a considerable time from the onset of plaque rupture and/or thrombi until the onset of AMI. These features may be predictors of AMI. The concept provides new insight into the mechanism and prevention of human AMIs.

Acute Disease↗
PubMed1999

Process of progression of coronary artery lesions from mild or moderate stenosis to moderate or severe stenosis: A study based on four serial coronary arteriograms per year.

BACKGROUND: The process of progression in coronary artery disease is unknown. METHODS AND RESULTS: The subjects were 36 patients with 36 objective vessels with clinically significant progression of coronary artery disease (>/=15% per year) in whom 4 serial coronary arteriograms (CAGs) were performed at intervals of approximately 4 months in a 1-year period. The degree of progression of percent stenosis between each of 2 serial CAGs was classified as marked (M: >/=15%), slight (S: 5% to 14%), and no progression (N: <5%). From the pattern of progression, the 36 vessels were classified as 14 type 1 vessels with marked progression (N-->N-->M in 13 vessels and S-->S-->M in 1 vessel) and 22 type 2 vessels without marked progression (S-->S-->S in 18 vessels, N-->S-->S in 4). Percent stenosis at the first, second, third, and final CAGs was 44+/-14%, 46+/-13%, 46+/-13%, and 88+/-10% (P<0.05 versus first CAG) in type 1 vessels and 44+/-11%, 50+/-9%, 59+/-9%, and 67+/-9% in type 2 vessels (P<0.05 for second, third, and final CAGs versus first CAG). Type 1 vessels featured the sudden appearance of severe stenosis due to marked progression, angina pectoris, or myocardial infarction (71%) and Ambrose type II eccentric lesions indicating plaque rupture or thrombi (57%). Type 2 vessels featured continuous slight progression of stenosis with smooth vessel walls; angina pectoris (14%) occurred when the percent stenosis reached a severe level. An increase in serum C-reactive protein was observed only in the type 2 vessel group, which suggests a relation between continuous slight progression and inflammatory change. CONCLUSIONS: Two types of stenosis progression provide a new insight into the mechanism of coronary artery disease.

Aged↗
PubMed1999

An ultrastructural study of the effects of bisphosphonate administration on osteoclastic bone resorption during relapse of experimentally moved rat molars.

This study was designed to clarify the effects of systemic administration of bisphosphonate, pamidronate, on the bone resorbing activity of osteoclasts during relapse of rat molars, after experimental movement. An elastic band was inserted between the upper first and second molars of 7-week-old rats and removed 21 days later. At 1 day before elastic band removal, bisphosphonate was administered via a tail vein. After elastic band removal, the rats were further maintained for 0, 5, or 10 days. The relapse of the first molars was studied by means of light and scanning-electron and transmission-electron microscopy. When an elastic band was removed, the mean interdental distance between the first and second molars in all rats was approximately 435 micrometer. In the control rats, it had decreased to 108 micrometer by day 5 and 57 micrometer by day 10. In these control rats, numerous osteoclasts appeared along the alveolar bone surface in the compressed side of the periodontal ligament of first molars. Administration of bisphosphonate significantly inhibited the prominent decrease in interdental distance. In these rats, it averaged 313 micrometer at day 5 and 115 micrometer at day 10. In bisphosphonate-treated rats, osteoclasts aggregated mainly in vascular canals of alveolar bone but were occasionally observed along the alveolar bone surfaces facing the periodontal ligament. Administration of bisphosphonate also induced structural changes, such as disappearance of ruffled borders and cytoplasmic polarity, in osteoclasts. A degenerated osteoclast was also observed in a bisphosphonate-treated rat. However, bisphosphonate induced no structural changes in osteoblasts, osteocytes, or periodontal ligament fibroblasts. These results suggest that a single systemic administration of bisphosphonate decreases the extent of initial relapse in experimentally moved rat molars via a mechanism involving impairment of the structure and resorptive functions of osteoclasts.

Alveolar Bone Loss↗
PubMed1999

Cellular roles in relapse processes of experimentally-moved rat molars.

This histological study was designed to clarify the relapse processes of rat molars following orthodontic tooth movement by the Waldo method. An elastic band was inserted between the upper first and second molars, and removed either 7 or 21 days later. The relapse processes of first molars were examined at 1 or 4 days after completing the 7-day-insertion and at 5 or 10 days after the end of the 21-day-insertion. At the end of the 7-day-insertion period, the mean interdental space was 158 microns, but decreased rapidly, reaching 44 microns by 1 day after removal, and 16 microns by day 4. In the periodontal ligament (PDL) compressed by elastic band insertion, partial hyalinization and/or mineralization occurred. The stretched PDL consisted of irregularly-distributed, thin principal fibres, approximately 2.4 microns in diameter. On days 1 and 4 after removal, osteoclasts, macrophage-like cells and fibroblast-like cells were localized around hyalinized tissues, but thick principal fibres, approximately 3.8 microns in diameter, were regularly distributed throughout the PDL proper. The mean interdental space after the 21-day-insertion was 536 microns, but this had decreased to 108 microns by day 5, and 71 microns by day 10. On day 5 after removal, numerous osteoclasts were evenly distributed in the compressed PDL, while thick principal fibres, approximately 3.5 microns, were present in the stretched PDL. These results suggest that, during relapse of experimentally-moved rat molars, (i) rapid remodelling of the PDL and surrounding alveolar bones is the main cause of tooth relapse and (ii) hyalinized and/or mineralized tissues occurred by compression are rapidly resorbed by osteoclasts, macrophage-like cells and fibroblast-like cells.

Alveolar Process↗
PubMed1997

Distributional changes of osteoclasts and pre-osteoclastic cells in periodontal tissues during experimental tooth movement as revealed by quantitative immunohistochemistry of H(+)-ATPase.

To investigate the mechanism of alveolar bone remodeling in response to orthodontic force application, we examined the distribution of osteoclasts and pre-osteoclastic cells using quantitative immunohistochemistry of vacuolar type H(+)-ATPase. For orthodontic force to be produced by the Waldo method, an orthodontic elastic band was inserted between the upper first and second molars of rats. The observed areas of periodontal tissues around second molars were the distal surfaces of mesial roots, as the pressure side, and the mesial surfaces of distal roots, as the tension side. Specific expression of vacuolar-type H(+)-ATPase at the ultrastructural level was detected in mononuclear and multinucleated pre-osteoclastic cells, as well as osteoclasts with ruffled borders on bone surfaces. At 6 hrs after orthodontic force application, many osteoclasts and pre-osteoclastic cells with H(+)-ATPase expression were first observed in vascular canals of the alveolar bone crest near the pressure side of the periodontal ligament, but the number of osteoclasts was not increased in the periodontal ligament. On day 1 after tooth movement, osteoclasts were increased in number in the periodontal ligament and in adjacent alveolar bones on the pressure side, but were seldom observed in corresponding areas on the tension side. The number of osteoclasts increased until day 7, but had decreased by day 14. These results suggest that, in bone remodeling during experimental tooth movement, (1) osteoclasts and pre-osteoclastic cells can be identified by H(+)-ATPase immunohistochemistry, (2) osteoclasts and pre-osteoclastic cells are rapidly induced after force application, (3) osteoclast induction first occurs in vascular canals of the alveolar bone crest on the pressure side, and then, (4) the number of osteoclasts increases in the periodontal ligament on the pressure side.

Alveolar Bone Loss↗
PubMed1990

Epidemiology of abomasal nematodes of dairy cattle in Hokkaido, northern Japan.

The prevalence and intensity of infection with abomasal nematodiasis was studied in dairy cattle of Hokkaido, northern Japan, for successive two years. During the period of March in 1985 to September in 1987, a total number of 393 abomasa of Holstein-Friesian cows was examined for nematode parasites. Nematodes were detected from 75% of the cows. The prevalence of nematode species detected was Ostertagia ostertagi 250 (63.6%), Mecistocirrus digitatus 181 (46.1%), Trichostrongylus axei 85 (21.6%) and Haemonchus sp. 1 (0.3%). The prevalence and population composition of each growth stage varied seasonally in O. ostertagi and M. digitatus. The large percentage of arrested larvae, early L4 O. ostertagi and immature L5 M. digitatus, detected during the mid-winter and the increasing percentage of matured adult populations of both species in early spring revealed the occurrence of the autumn associated arrested development (hypobiosis) phenomenon in bovine abomasum nematodes of Japan.

Abomasum↗