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Biomedical subjects

T Ohyama

Publications and source records attributed to T Ohyama.

321 records · Page 18Linked to original sources
PubMed1977

Effects of phthalate esters on the latent ATPase and swelling of mitochondria.

Phthalate esters have shown to stimulate the latent ATPase [EC 3.6.1.3] activity and induce mitochondrial swelling. Among the tested phthalate esters, di-n-butyl phthalate (DBP) exhibited the greatest activity, and the activity decreased progressively as the alkyl chain was lengthened or shortened. The DBP-stimulated ATPase was oligomycin-sensitive. The degree of stimulation of the ATPase was proportional to the extent of mitochondrial swelling induced by DBP in 0.1 M Tris-HCl (pH 7.2) containing 0.25 M sucrose. However, the swelling was dependent on the tonicity of the solution or the concentration of chloride ions, while the stimulation of ATPase was independent of these factors. Swelling was strongly induced by DBP at slightly acidic rather than neutral or alkaline pH. The pH-activity curve of DBP-stimulated ATPase was in inverse correlation with that of swelling, which showed a rather flat maximum at pH 8.0. When bovine serum albumin (BSA) was added to a solution containing mitochondria before addition of DBP, swelling was no longer caused by DBP, though the latent ATPase was stimulated to the same extent in the absence of added BSA.

Adenosine Triphosphatases↗
PubMed1976

Effects of phthalate esters on the respiration of rat liver mitochondria.

The effects of phthalate esters on the oxidation of succinate, glutamate, beta-hydroxybutyrate and NADH by rat liver mitochondria were examined and it was found that di-n-butyl phthalate (DBP) strongly inhibited the succinate oxidation by intact and sonicated rat mitochondria, but did not inhibit the State 4 respiration with NAD-linked substrates such as glutamate and beta-hydroxybutyrate. However, oxygen uptake accelerated by the presence of ADP and substrate (State 3) was inhibited and the rate of oxygen uptake decreased to that without ADP (State 4). It was concluded that phthalate esters were electron and energy transport inhibitors but not uncouplers. Phthalate esters also inhibited NADH oxidation by sonicated mitochondria. The degree of inhibition depended on the carbon number of alkyl groups of phthalate esters, and DBP was the most potent inhibitor of respiration. The activity of purified beef liver glutamate dehydrogenase [EC 1.4.1.3] was slightly inhibited by phthalate esters.

Adenosine Diphosphate↗
PubMed1975

Formate dehydrogenase. Subunit and mechanism of inhibition by cyanide and azide.

Formate dehydrogenase (EC 1.2.1.2) prepared from peas (Pisum sativum) was a two-subunit enzyme. The enzyme accelerated the formation of an NAD+-cyanide compound having an adsorption band at 330 nm. The enzyme was able to bind one NAD+ molecule per each subunit but only 1 mole of NAD+-cyanide compound was formed per two subunits. The complex of NAD+, cyanide, and the enzyme was very stable and had no catalytic activity. Azide inhibited the formate dehydrogenase reaction in two different ways. By incubation of the enzyme with azide in the presence of NAD+, half of its catalytic activity was lost. The remaining activity was also inhibited by azide but this inhibition was removed competively by formate. Contrary to the case of cyanide the inhibition by azide could be removed by dialysis and no spectral species due to the addition compound of NAD+ and azide could be observed. The data from double recipricol plots of the initial velocity and the formate concentration led to a conclusion that formate dehydrogenase has two sites with about equal catalytic activity. The Km for formate was different for the two catalytic sites (1.67 and 6.25 mM) but the difference was not noticeable in the case of the Km for NAD+.

Aldehyde Oxidoreductases↗
PubMedDate not supplied

Predominant role of local immunosuppressive effect in enhanced efficacy of liposomal FK506 in organ transplantation.

Liposomal FK506 is a new formulation of FK506 that increases FK506 levels in the liver and decreases them in the kidney in comparison to conventional IV formulation. In the present study, the efficacy of liposomal FK506 was evaluated in canine kidney and liver transplantation models. Liposomal FK506 increased the immunosuppressive efficacy of FK506 in the liver transplantation model, but decreased it in the kidney transplantation model. These results suggest that local immunosuppressive effects with increased intragraft FK506 level would play an important role in enhancing the immunosuppressive efficacy of liposomal FK506 in liver transplantation.

Animals↗
PubMedDate not supplied

The role of dopamine in the timing of Pavlovian conditioned keypecking in ring doves.

The effect of dopaminergic drugs on the timing of conditioned keypecking in ring doves was studied in two experiments. Subjects were given pairings of a keylight with food and the temporal distribution of keypecks was obtained during unreinforced probe trials. Experiment 1 demonstrated that injections of pimozide before each session immediately decreased response rates but shifted timing distributions gradually to the right over several days of treatment. Experiment 2 showed similar results using a longer interstimulus interval (ISI). No shifts were observed when the drug was injected after training sessions, or when a delay, identical to each subject's average latency to eat during the drug condition, was inserted between keylight offset and food presentation. Consequently, the shifts in timing were mediated neither by mere accumulation of the drug nor a delay from keylight offset to food presentation resulting from the drug's ability to slow motor processes. The results suggest that pimozide modulates response rate through its effect on motor processes or incentive value, and response timing through a conditioned response (CR) to injection-related cues established via their repeated pairings with the drug.

Amphetamine↗
PubMedDate not supplied

Rumors of disease in the global village: outbreak verification.

Emerging infectious diseases and the growth of information technology have produced new demands and possibilities for disease surveillance and response. Increasing numbers of outbreak reports must be assessed rapidly so that control efforts can be initiated and unsubstantiated reports can be identified to protect countries from unnecessary economic damage. The World Health Organization has set up a process for timely outbreak verification to convert large amounts of data into accurate information for suitable action. We describe the context and processes of outbreak verification and information dissemination.

Communicable Disease Control↗
PubMedDate not supplied

Effects of cyclic loading on the strength of all-ceramic materials.

PURPOSE: To investigate the effects of fatigue on the strength of materials used in all-ceramic crowns, the biaxial flexural strength of all-ceramic restorative materials was measured with precracked and laminated specimens after cyclic loading. MATERIALS AND METHODS: Two types of all-ceramic systems were used to prepare specimens: a glass-infiltrated alumina core system (In-Ceram) and a leucite-reinforced feldspathic porcelain system (IPS-Empress). Monolayer and laminated disks with a diameter of about 11.75 mm and a thickness of 1.20 +/- 0.05 mm were prepared. The biaxial flexural strength of the specimens that were polished and/or created with a precrack was measured. Their strength was also measured following cyclic loading. A cyclic load that was 60% of the mean breaking load of the specimens (before cyclic loading) was applied to specimens for 10(5) cycles in 37 degrees C water. RESULTS: Although 20% to 30% of the polished specimen samples fractured during cyclic loading, the biaxial flexural strength of specimens that survived the cyclic loading was nearly the same as that of specimens not subjected to the cyclic loading. The strength of the alumina system decreased with the introduction of precracks, and nearly all specimens fractured during cyclic loading. The strength of the leucite system, however, did not decrease with the presence of precracks, and no fractures were observed on these specimens during cyclic loading. CONCLUSION: These results suggest that although the alumina system has high flexural strength, it is more sensitive to flaws and susceptible to fatigue fracture. The effect of fatigue on the leucite system appears to be low.

Aluminum Oxide↗
PubMedDate not supplied

Gizzard nematodiasis in Japanese mountain hawk eagle (Spizaetus nipalensis).

In this paper, we report spontaneous gizzard nematodiasis in an adult Japanese mountain hawk eagle (Spizaetus nipalensis). Grossly, the gizzard had a black mucoid substance attached to the surface mucous membrane, and the heart was dilated. Histologically, immature larvae with yellow pigments invaded crypts of the mucous membrane. More developed larvae invaded the lamina propria and muscular layers and serosa of the gizzard, with pressure atrophy and cellular reaction (infiltration of heterophils and macrophages and proliferation of fibrous connective tissue). Moderate bronchopneumonia due to larvae invasion was also seen in the lung. The morphology suggests that the parasites may be nematodes, but the species of nematode could not be confirmed. The bird may have died from malabsorption and respiratory damage as a result of the gizzard and lung lesions.

Animals↗
PubMedDate not supplied

Proliferation of lung macrophages in acute fatal viral infections in chickens.

Marked proliferation of macrophages engulfing yellow pigments and fragmented erythrocytes were seen in the air capillaries and blood capillaries of the lungs of chickens affected with acute fatal viral hydropericardium syndrome, highly pathogenic infectious bursal disease, and highly pathogenic avian influenza. Proliferation of lung macrophages was associated with systemic proliferation of macrophages. Acute destruction of erythrocytes in these infections may have induced systemic hyperplasia of macrophages. The acute and severe proliferation of lung macrophages may cause acute respiratory dysfunction and be one of the factors inducing mortality in infected chickens. This syndrome may be categorized as "virus-associated hemophagocytic syndrome."

Acute Disease↗
PubMedDate not supplied

Stress analysis of metal-free polymer crowns using the three-dimensional finite element method.

PURPOSE: The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior metal-free crowns made of new composite materials. MATERIALS AND METHODS: A three-dimensional finite element model representing a mandibular first molar was constructed. Variations of the model had crowns of two types of composite, a glass ceramic, and porcelain fused to metal. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45-degree angle, and horizontally). RESULTS: The stress distributions in both types of composite crown were similar to that of the glass-ceramic crown. In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.9 to 18.3 MPa) concentrated around the loading points. In the masticatory force-stimulation test, the specimens experienced maximum tensile stresses of 20.3 to 26.6 MPa under a horizontal load and 10.9 to 11.0 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of composite and glass-ceramic crowns, and in the cervical area of the metal coping in the porcelain-fused-to-metal crowns. CONCLUSION: It would appear that the strength of occlusal contact points is important to the integrity of posterior metal-free crowns made of new composite materials and that bite forces applied from the horizontal direction are a critical factor determining success and failure.

Aluminum Silicates↗
PubMedDate not supplied

Rigidity of three different types of mandibular major connector through vibratory observations.

PURPOSE: The purpose of this study was to investigate the vibration characteristics of three different designs of mandibular major connectors in vitro by observing modal animation, decay rate, and maximum amplitude. MATERIALS AND METHODS: Three removable partial denture frameworks--lingual bar, Kennedy bar, and lingual plate--were studied. They were excited by a shaker, and the frequency response functions were recorded on a Fast Fourier Transformational analyzer to identify their modal shapes. Natural frequency and animation of motion at each natural mode of vibration of the three frameworks were observed. In addition, transient response simulations were recorded, and decay rates and maximum amplitude of the resultant transient response waves were computed. RESULTS: The mean decay rate calculated from all the measurement points of the lingual bar, Kennedy bar, and lingual plate was 3.10 s-1 (standard deviation [SD] 0.07), 2.42 s-1 (SD 0.04), and 2.01 s-1 (SD 0.03), respectively. Significant differences in decay rate were found among all pairs (P < .001). Maximum amplitude of the direct and indirect retainers at the nonimpacted side also differed (P = .008). CONCLUSION: All three designs demonstrated no elastic deformation at each natural mode of vibration. In terms of vibration analysis, the lingual bar demonstrated the maximum decay rate and the minimum maximum amplitude of the direct and indirect retainers, both on impacted and nonimpacted sides, indicating that the lingual bar will dissipate the energy through vibration faster than the other designs. Hence, the possibility of creating harmful effects to the oral tissue is lesser.

Analysis of Variance↗