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Biomedical subjects

M Tomikawa

Publications and source records attributed to M Tomikawa.

At least 19 recordsLinked to original sources
PubMed1991

Effect of ticlopidine and other antithrombotics on the venous thrombosis induced by endothelial damage of jugular vein in rats.

A venous thrombosis model was produced by vessel wall damage generated by freezing a small segment of the rat jugular vein. The process of thrombus formation was investigated by electron microscopic study. Ultrastructural studies demonstrated that the initiation of thrombus formation could be deendothelialization caused by freezing of vessel. When blood flow was reestablished, platelets adhered to subendothelium within 1 min. Then platelets aggregated on the adhering platelets, and fibrin net was formed. Finally, thrombi composed predominantly of fibrin and red blood cells with platelet aggregates and leukocytes were generated. An anti-platelet agent, ticlopidine, revealed a potent antithrombotic effect in this model. Because ticlopidine decreased the number of platelet aggregates, reduced the size of aggregates, and inhibited platelet degranulation, it is conceivable that platelet aggregation in early phase of thrombus formation plays a crucial role even in venous thrombosis model. A synthetic thrombin inhibitor, argatroban, also showed a potent antithrombotic effect, but a thrombolytic agent, urokinase, was less effective. In conclusion, this model is both platelet- and coagulation-dependent.

Animals↗
PubMed1990

Dissolution of emboli in rats with experimental cerebral thromboembolism by recombinant human tissue plasminogen activator (TD-2061).

Tissue plasminogen activator (t-PA) is frequently administered clinically as thrombolytic therapy. We injected recombinant t-PA into rats with cerebral 125I-labeled blood clot emboli to evaluate the dissolutive effect of recombinant human single-chain t-PA (rt-PA; TD-2061) on such emboli and to examine the possibility of improving neurological damage in patients with cerebral thrombosis. When rt-PA was given intravenously at a dose of 350,000 IU/kg 2 minutes before embolization, radioactivity in the affected cerebral hemisphere decreased to 20% of that in the vehicle control 2 hours after embolization. A significant decrease in radioactivity in the cerebral hemisphere was also found on the administration of 700,000 IU/kg of rt-PA 30 or 60 minutes after embolization, but not when rt-PA was administered 2 minutes after embolization. Marked inhibition of abnormal behavior such as hemiplegia was seen on treatment with rt-PA 2 minutes before embolization, but not at all when rt-PA treatment was given 30 or 60 minutes after embolization. The findings suggest that rt-PA can dissolve blood clot emboli in cerebral vessels and that prompt thrombolytic therapy is important to minimize neurological dysfunction in cases of cerebral thromboembolism.

Animals↗
PubMed1990

Arterial injury-induced smooth muscle cell proliferation in rats is accompanied by increase in polyamine synthesis and level.

Proliferation of smooth muscle cells (SMC), enhancement of polyamine biosynthesis and increase in polyamine level in response to deendothelialization in the rat aorta were studied. [3H]Thymidine incorporation into SMC in aortas denuded with a balloon catheter began 25 h after injury, and maximal incorporation occurred 33-37 h after injury. Afterwards, [3H]thymidine incorporation declined, approaching the baseline level, but was slightly higher than that of sham-operated controls until 14 days after injury. Intimal thickening started 7 days after injury, and peaked at 21 days. Prior to these proliferative changes in aortic SMC, a rapid and transient increase in ornithine decarboxylase (ODC) activity was observed within 8 h after injury. There was no significant difference in ODC activity between injured and intact aortas after 4 days. The levels of polyamines, putrescine, spermidine, and spermine increased and were maximal at 48 h after injury, 8.1, 3.4 and 1.4 times the control levels, respectively. Increased levels of polyamines, in particular spermidine, continued until 7 days after injury. These results suggest that the enhancement of polyamine synthesis and the increased polyamine content of the aorta play important roles in the proliferation of SMC and in the development of intimal thickening, particularly in the initial proliferative response of medial SMC after deendothelialization.

Animals↗
PubMed1989

Specific induction of 68 KD protein synthesis in rabbit smooth muscle cells by growth stimuli in platelets: comparison of intimal and medial SMC.

We examined the influence of growth stimuli in heat-treated platelet extract on specific protein synthesis in the early phase of the cell cycle prior to the initiation of DNA synthesis in cultured rabbit aortic smooth muscle cells (SMC). The extract preferentially stimulated the synthesis of a cytoplasmic protein with a molecular weight of 68000 (p68) and an isoelectric point of around 6.3. Stimulation of p68 synthesis occurred within 1 h after the addition of heat-treated platelet extract to growth-arrested and quiescent SMC, continued until 4 h after stimulation, and then returned to the baseline level. Actinomycin D preferentially inhibited p68 synthesis. In SMC prepared from atheromatous plaques from the aorta of hyperlipidemic rabbits (I-SMC), the amount of DNA synthesis and of p68 synthesis by heat-treated platelet extract were less than those of SMC prepared from normal media (M-SMC), suggesting that the decreased capacity for cell proliferation of I-SMC in response to heat-treated platelet extract was due to the down-regulation of signal transduction in the early G0/G1 phase of the cell cycle.

Animals↗
PubMed1989

Studies on intimal smooth muscle cells in rabbits: decreased growth response to the tumor promoter.

The growth behavior of intimal smooth muscle cells (SMC) prepared from atheromatous plaques of the thoracic aorta in hyperlipidemic rabbits was studied in a culture system. Specimens of intimal and normal medial SMC were examined in terms of their proliferative response to various growth factors, polypeptide hormones or 12-O-teradecanoylphorbol-13-acetate (TPA). Intimal SMC showed lower rates of growth and DNA synthesis when the cells were exposed to TPA, but there was no difference in growth response between intimal and medial SMC to the other growth-promoting stimuli such as fibroblast growth factor (FGF), epidermal growth factor (EGF), insulin or serotonin. 3H-phorbol-12,13-dibutyrate (3H-PDBu) binding assays showed the number of binding sites to phorbol esters in intimal SMC to be decreased by 65% as compared with that in medial SMC. These results suggested that intimal SMC have different growing characteristics, which seemed to be acquired during the process of intimal thickening.

Animals↗
PubMed1988

Effect of probucol on macrophages, leading to regression of xanthomas and atheromatous vascular lesions.

To explain the strong effect of probucol on xanthomas, the drug's effect on lipid storage in macrophages in the presence of denatured low-density lipoprotein (LDL) was studied. Two macrophage cell lines, UE-12 and THP-1, were used. Those cells stored lipids and became foam cells when they were incubated with acetylated LDL (acetyl-LDL). When probucol was added into the medium either in ethanolic solution or in the form bound to LDL, the storage of cholesterol and other lipids and the development of macrophages into foam cells were greatly suppressed. Two functions of probucol should be considered: (1) It inhibited the uptake of acetyl-LDL by macrophages; and (2) it enhanced the release of cholesterol from these cells. Cells were first incubated with probucol. After the cells were washed with fresh medium, the radiolabeled acetyl-LDL was added to the medium and the degradation of acetyl-LDL was measured. Increasing the concentration of probucol led to a decrease in degradation of acetyl-LDL by macrophages. Probucol also suppressed the uptake of albumin. Macrophages were incubated with acetyl-LDL, washed once, then incubated with or without probucol and high-density lipoprotein (HDL). Addition of HDL caused a rapid decrease in cholesterol content in the cells, and this phenomenon was enhanced by probucol for both kinds of cells. The secretion of apolipoprotein E was also stimulated by the addition of probucol. These 2 sets of experimental results suggest that probucol prevents lipid storage in macrophages by both suppressing the uptake and stimulating the release of cholesterol and other lipids into or from the macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriosclerosis↗
PubMed1988

Morphology and increased growth rate of atherosclerotic intimal smooth-muscle cells.

Atherosclerotic intimal smooth-muscle cells (SMCs) in vitro showed higher growth activity than did medial SMCs obtained from either atherosclerotic or normal aortas. Using an electron microscope, it was proved in primary cultures by an explant method that intimal SMCs had rich organelles and fewer filaments in their cytoplasms. They were regarded as synthetic phenotype. In contrast, most medial SMCs had rich filaments and fewer organelles. They were regarded as contractile phenotype. When atherosclerotic intimal and normal medial SMCs were plated on type I collagen gel, cytoplasmic cyclic adenosine monophosphate concentration increased and DNA synthesis was suppressed. Intimal SMCs cultured on the gel showed contractile phenotype. Dibutyryl cyclic adenosine monophosphate added to culture media decreased DNA synthesis and altered cellular phenotype to a contractile state. Intimal SMCs were more resistant to injury by hyperlipidemic low-density liproprotein and homocysteine. Lysosomal enzyme activity was enhanced in intimal SMCs.

Animals↗
PubMed1986

Mode of action of probucol in reducing serum cholesterol in mice.

The mode of action of probucol in reducing serum cholesterol was studied in normal and cholesterol-fed mice. Probucol did not affect intestinal absorption of radioactive cholesterol in normal and cholesterol-fed mice. In normal mice, probucol treatment resulted in inhibition of incorporation of [14C]-acetate into cholesterol in the liver, while it stimulated the incorporation in the small intestines. Incorporation of [14C]-mevalonate into cholesterol was not affected by the treatment. These results were consistent with the finding that the HMG-CoA reductase activity was decreased in the liver, but increased in the intestinal tissues of the treated mice. In cholesterol-fed mice, probucol treatment had no effect on cholesterol synthesis in the liver, while it increased the intestinal cholesterol synthesis. The over-all effect of this drug on cholesterol synthesis was not significant, although it tended to be inhibitory in normal mice and stimulatory in cholesterol-fed mice. On the other hand, probucol treatment resulted in acceleration of the clearance of [14C]-cholesterol-derived radioactivity from the circulation and resulted also in a significant increase in fecal excretion of the radioactivity, cholesterol and bile acids without changes in lipid composition of the bile. Cholesterol content in and radioactivity distribution among the tissues were not affected by probucol. Hepatic cholesterol 7 alpha-hydroxylase activity was increased by probucol. These findings indicate that probucol lowers serum cholesterol mainly by increasing catabolic excretion of cholesterol into bile.

Animals↗
PubMed1986

Effect of probucol, pantethine and their combinations on serum lipoprotein metabolism and on the incidence of atheromatous lesions in the rabbit.

Effect of probucol, pantethine and their combinations on serum lipoprotein metabolism and on the incidence of atheromatous lesions in aorta and coronary artery was studied in cholesterol-fed rabbits. Probucol treatment (0.5% in diet) resulted in reducing HDL cholesterol and serum apo A-I levels significantly, while pantethine treatment (0.25%-0.75% in diet) tended to increase HDL cholesterol and serum apo A-I levels. Combined treatment with these two drugs showed a significant prevention in the reduction of HDL cholesterol and serum apo A-I levels by probucol alone. Probucol or pantethine treatment reduced effectively (V) LDL cholesterol and serum apo B levels, and these effects were accelerated additively when the two drugs were given concurrently. Atheromatous lesions in aorta and coronary artery in cholesterol-fed rabbits were prevented by the treatment with probucol (0.5% in diet) or pantethine (0.75% in diet) for 24 weeks. The combined treatment with these two drugs showed more marked prevention than either drug alone. From these findings, it is concluded that the combined treatment of probucol with pantethine is effective for improvement of serum lipoprotein disorders and for prevention of the incidence of atheromatous lesions in aorta and coronary artery in cholesterol-fed rabbits.

Animals↗
PubMed1985

Action of malotilate on reduced serum cholesterol level in rats with carbon tetrachloride-induced liver damage.

The mode of action of malotilate in normalizing serum cholesterol in hypocholesterolemic rats with fatty liver was examined by determination of biosynthesis, catabolism and excretion of cholesterol. Fatty liver was produced by subcutaneous injection of CCl4 at the dose of 1 ml/kg into male rats (SLC-SD) twice a week for 3 weeks. Daily administration of malotilate (100 mg/kg) in rats with hypocholesterolemia resulted in a rapid normalization of lowered serum cholesterol. Such a recovery of cholesterol level in serum coincided in time with normalization of the decreased cholesterol level of each lipoprotein fraction, VLDL-triglycerides secretion and the decreased apolipoprotein A1 value. Histopathological improvement in liver was also confirmed by a decrease in the size of fat droplets stored within the hepatocytes. The malotilate treatment gave a tendency to facilitate hepatic cholesterol synthesis in rats with fatty liver. Malotilate at a concentration of 0.5-2 micrograms/ml also stimulated cholesterol biosynthesis in cultured normal hepatocytes. The drug had the action to accelerate the catabolic excretion of 3H-labeled cholesterol into feces. These results suggest that the mode of action by which serum cholesterol is normalized in rats with fatty liver is probably due to a stimulative effect of malotilate on hepatic cholesterol synthesis and cholesterol secretion from the liver.

Animals↗
PubMed1978

[Fibrinogen: structure, function and interaction with proteins and cells].

The dimerous three-chained protein fibrinogen has at its disposal different functional zones which are included in the process of polymerisation and which possess importance for the specific reaction of fibrinogen with certain cells. The present paper is particularly engaged with the activation of fibrinogen by thrombin and with the mechanism of the arrangement of the activated units of fibrinogen concerning the fibrin fibre. Finding concerning the interaction of the platelets with fibrinogen connected to sepharose plead for the fact that a change of conformation in the molecule of fibrinogen precedes the specific platelet reaction.

Blood Platelets↗
PubMed1975

Patho-physiological studies on lactic acid-induced pulmonary thrombosis in rat. I. Effect of heparin, acetylsalicylic acid, urokinase and tranexamic acid.

The role of platelet aggregation and coagulo-fibrinolytic systems in thrombogenesis of lactic acid-induced pulmonary thrombosis in rat were studied using an anti-coagulant, platelet aggregation inhibitor, fibrinolytic or anti-fibrinolytic agents. In normal rat, heparin (2.5 mg/kg), acetylsalicylic acid (30 mg/kg) and tranexamic acid (100 mg/kg) suppressed specifically coagulation, platelet aggregation induced by collagen or thrombin and fibrinolysis respectively. Urokinase (10,000 units/kg) activated powerfully fibrinolytic system in addition to suppressing slightly platelet aggregation. The pretreatment with heparin, acetylsalicylic acid or urokinase markedly prevented the formation of thrombus initiated by the infusion of lactic acid at the doses used. Additive effect was also obtained by combined administration of these agents. On the other hand, it was interesting to note that tranexamic acid (100 mg/kg) did not affect the thrombus formation at all despite a potent anti-fibrinolytic effect of this agent. These results indicate that both platelet aggregation and enhancement of coagulation activity are important factors responsible for the formation of thrombi in DIC, while the fibrinolytic activity in blood seems not to be involved in it. On the basis of the findings, mechanism for triggering activation of coagulation and platelet aggregation is also discussed here.

Animals↗