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Biomedical subjects

H Shimokawa

Publications and source records attributed to H Shimokawa.

At least 127 records · Page 7Linked to original sources
PubMed1996

Microgravity induces prostaglandin E2 and interleukin-6 production in normal rat osteoblasts: role in bone demineralization.

It has been suggested that microgravity alters bone metabolism. Evidence for this phenomenon includes the negative calcium balance and decreased bone density in astronauts, as well as, inhibition of bone formation in rats flown for 2 to 3 weeks. However, the specific mechanisms that modulate these changes in microgravity are unknown. The purpose of this study was to clarify the mechanism of microgravity-induced bone demineralization using normal rat osteoblasts obtained from femur marrow cultures. The osteoblasts were cultured for 5 days during a Shuttle-Spacelab flight (STS-65). After collection of the culture medium, the cellular DNA and RNA were fixed on board. Enzyme-immunoassay of the culture medium for prostaglandin E2 (PGE2) indicated that microgravity induced a 4.5- to 136-fold increase in flight samples as compared to the ground control cultures. This increase of PGE2 production was consistent with a 3.3- to 9.5-fold elevation of inducible prostaglandin G/H synthase-2 (PGHS-2) mRNA, quantitated by reverse transcription-polymerase chain reaction (RT-PCR). The mRNA induction for the constitutive isozyme PGHS-1 was less than that for PGHS-2. The interleukin-6 (IL-6) mRNA was also increased (6.4- to 9.3-fold) in microgravity as compared to the ground controls. Since PGE2 and IL-6 are both known to play a role in osteoclast formation and bone resorption, these data provide molecular mechanisms that contribute to our understanding of microgravity-induced alterations in the bone resorption process.

Animals↗
PubMed1996

Chronic treatment with interleukin-1 beta induces coronary intimal lesions and vasospastic responses in pigs in vivo. The role of platelet-derived growth factor.

Studies in vitro have suggested that inflammatory cytokines may play an important role in the pathogenesis of atherosclerosis. However, little is known about their effects in vivo. Thus, the present study was designed to determine in vivo what histological and functional changes may be induced by chronic treatment with IL-1 beta, one of the major inflammatory cytokines, and also to clarify what mechanisms are involved in those changes. Under aseptic conditions, proximal segments of the left porcine coronary arteries were gently wrapped with cotton mesh absorbing Sepharose beads either with or without recombinant human IL-1 beta. From 1 to 4 wk after the operation, coronary vasospastic responses to intracoronary serotonin or histamine were noted at the IL-1 beta-treated site but not at the control site. Histologically, intimal thickening was greater at the IL-1 beta-treated site than at the control site. Those functional and histological changes induced by the chronic treatment with IL-1 beta were significantly inhibited by the simultaneous treatment with a neutralizing antibody to either IL-1 beta or PDGF. These results indicate that chronic treatment with Il-1 beta induces coronary intimal lesions and vasospastic responses in porcine coronary arteries in vivo and also suggest that these changes are substantially mediated by PDGF.

Animals↗
PubMed1996

In vivo and in vitro association of retinoic acid with form-deprivation myopia in the chick.

The purpose of this study is to clarify the role of retinoic acid (RA) in the mechanism of form-deprivation myopia (FDM) in the chick. FDM was induced in two-day old chicks by placement of a translucent plastic goggle over one eye, with the contralateral eye used as a control. After 12 days, the chicks were euthanized. RNA was extracted from scleras in the posterior segments, transcribed into cDNA, and amplified by PCR with primers specific for retinoic acid receptor (RAR) beta. G3PDH was used as a reference gene for normalization. The effects of RA, with or without TGF-beta, on the proliferation of scleral chondrocytes and scleral fibroblasts from 17-day chick embryos were studied by use of a colorimetric assay, and the alkaline phosphatase activities of those cells also studied. Furthermore, RAR beta expression in response to RA in cultured scleral cells was studied. As a result, RT-PCR products of the expected sizes were obtained from scleras from the myopic and control eyes. Expression of RAR beta in the myopic scleras was significantly higher than that in the controls. The proliferation of scleral chondrocytes and scleral fibroblasts was inhibited by treatment with RA in a dose-dependent manner (in 10% FBS). In the presence of TGF-beta (in 0.5% FBS), RA treatment stimulated the proliferation of scleral chondrocytes but inhibited the proliferation of scleral fibroblasts. RA induced alkaline phosphatase activities in both the scleral chondrocytes and scleral fibroblasts. RAR beta expression was induced by RA in cultured scleral cells. These results demonstrate that RA appears to play a role in the mechanism of FDM in the chick. However, it is also possible that the changes in the expression of RAR beta were secondary events related to other mechanisms responsible for ocular enlargement.

Alkaline Phosphatase↗
PubMed1996

Basal release of endothelium-derived nitric oxide at site of spasm in patients with variant angina.

OBJECTIVES: The aim of this study was to investigate the basal release of nitric oxide at spastic sites in patients with variant angina. BACKGROUND: We previously reported that endothelium-dependent dilator responses to acetylcholine, substance P and bradykinin are preserved at the site of coronary artery spasm. However, it is not known whether the basal release of endothelium-derived nitric oxide is altered at the spastic site. METHODS: The effects of intracoronary N(G)-monomethyl-L-arginine (L-NMMA, an inhibitor of nitric oxide synthesis) at cumulative doses of 50, 100 and 200 micromol on basal coronary artery tone were investigated in eight patients with variant angina and normal coronary angiograms and in eight control subjects. The lumen diameters of large epicardial coronary arteries were assessed by quantitative coronary arteriography. RESULTS: Coronary spasm was provoked by the intracoronary administration of acetylcholine in all patients with variant angina. L-NMMA did not alter the arterial pressure and heart rate but significantly decreased the coronary artery diameter at spastic and nonspastic sites. Constrictive responses to L-NMMA were significantly greater (p < 0.01) at the spastic site (constriction by 200 micromol, 22+/-7%, mean +/- SD) than at the nonspastic site (10+/-7%). Constrictive responses to L-NMMA at the nonspastic site in patients with variant angina were comparable to those in the control subjects. CONCLUSIONS: These findings support the hypothesis that the basal release of nitric oxide may not be decreased at the spastic site in patients with variant angina.

Aged↗
PubMed1996

Tyrosine kinase inhibitor suppresses the (re) stenotic changes of the coronary artery after balloon injury in pigs.

OBJECTIVE: Restenosis after percutaneous transluminal coronary angioplasty (PTCA) still remains a serious late complication. Many growth factors induced in restenotic lesions may be responsible for restenosis after PTCA. Most of the receptors for such growth factors possess tyrosine kinase activity. This study was designed to determine whether or not a specific tyrosine kinase inhibitor, ST 638, can prevent (re)stenotic changes of the coronary artery after balloon injury. METHODS: A segment of the porcine coronary artery was aseptically wrapped with cotton mesh absorbing either ST 638 or vehicle, followed by balloon injury. Two weeks after the procedure, coronary stenosis and vasoconstricting responses were examined by coronary arteriography and (re)stenotic changes of the coronary artery were histologically examined. Antiphosphotyrosine immunoblotting was also performed to examine the inhibitory effects of ST 638. RESULTS: Coronary arteriography showed the development of mild stenotic lesions at the balloon-injured sites, where hyperconstrictive responses were repeatedly induced by intracoronary serotonin and histamine. Histologically, neointimal formation was noted at the balloon-injured site, where the total vessel area also tended to decrease (geometric remodeling). The treatment with ST 638 suppressed all the hyperconstrictive responses, the neointimal formation, and the geometric remodeling induced by balloon injury. Immunoblotting for phosphotyrosine proteins demonstrated the elevation of proteins at the balloon-injured site, which was suppressed by ST 638. CONCLUSIONS: These results indicate that tyrosine kinases are activated at the balloon-injured site and the inhibition of such kinase activities is effective in reducing both the (re)stenotic changes (neointimal formation and geometric remodeling) and the hyperconstrictive responses of the coronary artery after balloon injury.

Angioplasty, Balloon, Coronary↗
PubMed1996

Coronary vascular ATP-sensitive potassium channels are activated to a greater extent in spontaneously hypertensive rats than in Wistar-Kyoto rats.

OBJECTIVE: To determine whether opening of coronary vascular adenosine 5'-triphosphate (ATP)-sensitive potassium (KATP) channels is involved in the maintenance of resting coronary flow in hypertrophied hearts. METHODS: We examined the effects of glibenclamide, a selective inhibitor of KATP channels, on basal coronary vascular tone in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Using a Langendorff system, the hearts from WKY rats and SHRs were isolated and perfused with oxygenated Krebs-Henseleit solution at a constant perfusion pressure of 60 and 100 mmHg respectively. RESULTS: Basal coronary flow and myocardial oxygen consumption (MV02) were similar in SHRs and WKY rats. The percentage decreases in coronary flow with glibenclamide at graded doses were greater (P < 0.01) in SHRs than in WKY rats (n = 8), whereas the percentage decreases in MV02 with glibenclamide were similar in the two groups. The decreases in coronary flow caused by U46619 (a thromboxane A2-mimetic agent) were similar in SHRs and WKY rats (n = 4). The increase in coronary flow caused by pinacidil (a KATP opener) was greater in SHRs than in WKY rats; glibenclamide prevented the pinacidil-induced increase in coronary flow in both SHRs and WKY rats. There was a significant positive correlation between the glibenclamide-induced decrease in coronary flow and the degree of left ventricular hypertrophy (r = 0.54, P < 0.05). CONCLUSION: Our results suggest that the basal opening state of coronary vascular KATP channels is activated to a greater extent in SHRs than WKY rats, which may contribute to the maintenance of basal myocardial perfusion in hypertrophied hearts.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

Endothelial Gi protein expression is markedly low in human coronary microvessels.

Gi protein functionally mediates endothelium-dependent relaxations in large epicardial coronary arteries but not in small coronary arteries, which suggests a different involvement of Gi protein in the endothelium-dependent relaxations between large and small coronary arteries. We previously showed that endothelial Gi protein is present in human epicardial coronary artery. In the present study, we examined the expression of endothelial Gi protein in human coronary microvessels. Immunohistochemical staining with a specific antibody against human Gi protein was performed in intramyocardial coronary microvessels and vasa vasorum from 34 autopsy cases. The immunoreactive levels of the endothelial Gi protein were semiquantitated into four grades (none, 0; slight, +1; moderate, +2; high, +3), and the mean value of the ratings of all endothelial cells was then used as an index of the endothelial Gi protein expression of the vessel. The immunoreactive levels of the endothelial Gi protein were extremely low in intramyocardial coronary microvessels and in vasa vasorum, irrespective of the age of the patients, the presence or absence of coronary risk factors, or the influence of medical treatments. These results may therefore explain in part why endothelium-dependent relaxations in coronary microvessels are not functionally mediated by Gi protein.

Adolescent↗
PubMed1996

The importance of the hyperpolarizing mechanism increases as the vessel size decreases in endothelium-dependent relaxations in rat mesenteric circulation.

Endothelium-dependent relaxations are achieved by a combination of endothelium-derived prostacyclin (PGI2), nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). However, it remains to be fully clarified whether the relative contribution of these three mechanisms to endothelium-dependent relaxations varies as a function of the vessel size. This study was designed to clarify this point. Acetylcholine (ACh)-induced endothelium-dependent relaxations were examined in isolated blood vessels taken from the aorta and the proximal and distal mesenteric arteries of the rat. The contributions of PGI2, NO, and EDHF were evaluated by the inhibitory effects of indomethacin, N omega-nitro-L-arginine methyl ester (L-NAME) in the presence of indomethacin, and KCl in the presence of indomethacin and L-NAME, respectively. The membrane potentials were recorded with microelectrodes. The expression of endothelial No synthase (eNOS) was examined by both immunostaining and immunoblotting. The contribution of PGI2 was negligible in three different-sized blood vessels. The contribution of NO was most prominent in the aorta, whereas that of EDHF was most prominent in the distal mesenteric arteries. The resting membrane potential was significantly deeper and the ACh-induced hyperpolarization was greater in the distal mesenteric arteries than those in the aorta. The expression of eNOS was the highest in the aorta and the lowest in the distal mesenteric arteries. These results indicate that the importance of EDHF increases as the vessel size decreases in endothelium-dependent relaxations in the rat mesenteric circulation.

Acetylcholine↗
PubMed1996

Identification of the cell type origin of odontoma-like cell masses in microphthalmic (mi/mi) mice by in situ hybridization.

Tooth abnormalities occur in microphthalmic (mi/mi) mice. The elongated odontogenic epithelium is interrupted by unresorbed bone at the basal end of the mi/mi incisor, with the epithelium gathered into cell clusters. These clusters develop to odontoma-like masses. To identify the origin of the cell types of these odontoma-like masses, the localization of osteonectin (Osn), osteocalcin (Osc), osteopontin (Osp), matrix Gla protein (MGP) and amelogenin (Am) mRNA in the process of tooth development in mi/mi and +/+ mice was investigated by means of in situ hybridization. Decalcified mandibles of neonatal, 5-, 10-, 14-day-old mice were examined. Osn and Osc mRNA, which localized in osteoblasts and odontoblasts, were also detected in the cells of odontoma-like masses in mi/mi mice. The cells expressing these mRNA were short, columnar and odontoblast-like. Am mRNA was detected in ameloblasts. In mi/mi mice, Am mRNA was also detected in ameloblastic cell clusters, which were formed by the tall columnar cells in the odontoma-like masses. No apparent Osp mRNA expression was detected in the masses. These results indicated that even in odontogenic abnormal cells resulting from physical obstruction in mi/mi mice, the genes that are involved in normal tooth development were still expressed.

Animals↗
PubMed1996

PKC inhibitors prevent endothelial dysfunction after myocardial ischemia-reperfusion in rats.

The intracellular mechanism for endothelial dysfunction after myocardial ischemia-reperfusion remains to be elucidated. It has been reported that activation of protein kinase C (PKC) occurs after myocardial ischemia-reperfusion and that the activation impairs endothelium-dependent relaxation. Thus we examined the role of PKC activation in the ischemia-reperfusion-induced endothelial dysfunction. Isolated rat hearts perfused with a constant flow were subjected to global ischemia for 15 min followed by reperfusion for 20 min. Coronary vascular responses to the endothelium-dependent vasodilators acetylcholine (ACh) and bradykinin (BK) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were examined before and after the ischemia-reperfusion. Endothelium-dependent relaxations to ACh and BK were impaired after the ischemia-reperfusion, whereas endothelium-independent relaxations to SNP were unaffected. Pretreatment with a PKC inhibitor, staurosporine, H7, or calphostin C, prevented the impairments. Phorbol 12-myristate 13-acetate, a PKC-activating phorbol ester, attenuated the relaxations to ACh and BK but not those to SNP. These results suggest that PKC activation may be involved in part in the ischemia-reperfusion-induced endothelial dysfunction.

Animals↗
PubMed1996

ATP-sensitive K+ channel opener pinacidil augments beta 1-adrenoceptor-induced coronary vasodilation in dogs.

The opening of ATP-sensitive K+ (K+ATP) channels contributes to the mechanism of metabolic coronary vasodilation. The aim of the present study was to determine whether K+ATP channel opener pinacidil augments coronary vasodilation induced by beta-adrenoceptor stimulation. In anesthetized dogs, coronary vasodilation in response to intracoronary infusion of a beta 1-adrenoceptor agonist denopamine, selective beta 2-adrenoceptor stimulation with isoproterenol after bisoprolol or nitroglycerin was studied before and during simultaneous intracoronary infusion of pinacidil at a dose of 1 microgram/min, which had no effect on basal hemodynamics. Pinacidil augmented the denopamine-induced increase in coronary blood flow (CBF) from 38 +/- 9 to 66 +/- 16% (P < 0.05) but did not affect the denopamine-induced by isoproterenol or nitroglycerin. Thus pinacidil selectively augmented beta 1-adrenoceptor-mediated coronary vasodilation. These observations suggest that the K+ATP channel opener pinacidil may increase myocardial perfusion during metabolic stress associated with beta 1-adrenoceptor stimulation.

Adenosine Triphosphate↗
PubMed1996

Vanadate causes synthesis of endothelium-derived NO via pertussis toxin-sensitive G protein in pigs.

The effects of sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, on the endothelial nitric oxide (NO) pathway were studied in vitro. Vanadate caused endothelium-dependent relaxations in isolated porcine coronary arteries, which were abolished by N omega-nitro-L-arginine methyl ester. The relaxations were also abolished by pertussis toxin, an inhibitor of certain G proteins. Tyrosine kinase inhibitors, genistein and alpha-cyano-3-ethoxy-4-hydroxy-5-phenyl-methylcinnamamide (ST-638), significantly attenuated the vanadate-induced relaxations. Vanadate also caused pertussis toxin-sensitive, endothelium-dependent relaxations in isolated porcine renal and femoral arteries and jugular veins. Immunoblots, using an antibody to phosphotyrosines and to c-Src in native porcine aortic endothelial cells, respectively, showed that vanadate induced an elevation of phosphotyrosine proteins and a decrease in the amount of the active form of c-Src family kinases; both changes were markedly suppressed by cotreatment with ST-638. These results indicate that in porcine blood vessels, vanadate causes a synthesis of endothelium-derived NO for which endothelial tyrosine kinases and pertussis toxin-sensitive G protein are considered to be closely involved.

Animals↗
PubMed1996

Gene expression and localization of amelogenin in the rat incisor.

Gene expression and localization of amelogenin were studied in the developing rat incisor by the methods of in situ hybridization and immunohistochemistry. ISH revealed the first expression of amelogenin mRNA in the inner enamel epithelium of the cervical loop. The signals were clearly observed in pre-ameloblasts in the region bordering on predentin formation and became more intense toward the cells on the initial enamel matrix secretion. The maximal signals were found in the cytoplasm of secretory ameloblasts. From the terminal secretion zone, the signals then became gradually weaker toward the incisal edge but were still evident in the cytoplasm of shortening, transitional ameloblasts and those at the early maturation stage. No signals were found in the cells of the stratum intermedium and stellate reticulum throughout amelogenesis. Immunohistochemistry by means of an antibody against amelogenin C-telopeptide consisting of 12 amino acids revealed immunoreaction in the secretory ameloblasts reacting to the ISH. When a polyclonal antibody against amelogenin was used, immunoreaction was found in the distal ends of ruffle-ended ameloblasts (RA) in the maturation zone. Those results indicated that amelogenin is synthesized by ameloblastic cells from the inner enamel epithelium to the early maturation stage and is then resorbed by the RA.

Ameloblasts↗
PubMed1996

Effect of cilostazol, a novel anti-platelet drug, on restenosis after percutaneous transluminal coronary angioplasty.

The possible preventive effect of cilostazol, a novel anti-platelet drug, on restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) was examined. One hundred and two consecutive patients, who underwent successful PTCA, were followed for 3 to 6 months. To prevent restenosis, 46 patients (60 PTCA sites) were treated with cilostazol alone (200 mg/day) (cilostazol group) and the remaining 56 (61 PTCA sites) were treated with other anti-platelet drugs and/or warfarin potassium (control group). Restenosis was defined as a more than 50% loss of the initial gain of the coronary diameter achieved by PTCA. Cilostazol did not significantly reduce the patient or lesion restenosis rate; the patient restenosis rate was 32% in the control group and 22% in the cilostazol group (P = 0.24), and the lesion restenosis rate was 30% in the control group and 23% in the cilostazol group (P = 0.44). However, the lesion non-progression rate, which was defined as the incidence of lesions with either no change or regression of coronary stenosis at the PTCA site, was significantly greater with cilostazol (37%) than in the control group (16%) (p < 0.05). Although cilostazol failed to show a significant reduction in restenosis after PTCA, the present results suggest that a further trial with a larger number of patients is needed to confirm its usefulness.

Aged↗
PubMed1996

Granulocyte activation in restenosis after percutaneous transluminal coronary angioplasty.

To examine whether or not granulocyte activation is involved in restenosis after percutaneous transluminal coronary angioplasty (PTCA), we prospectively followed the time course of the plasma level of granulocyte elastase, which is an index of granulocyte activation, before and after successful angioplasty in 43 consecutive patients. Restenosis was defined as a more than 50% loss of the initial gain in the coronary diameter achieved by PTCA with more than a 50% resultant stenosis in the follow-up coronary arteriography performed 3 months after PTCA. There was no difference in the level of granulocyte elastase between the 2 groups with (n = 15) and without (n = 28) restenosis before, the day after and 1 month after PTCA. However, 3 months after PTCA, the level of granulocyte elastase was significantly higher in the group with restenosis than in that without restenosis (171 +/- 13 vs 147 +/- 6 mg/l, P < 0.05). The level of granulocyte elastase at 3 months after PTCA also correlated significantly with the percent luminal stenosis at the angioplasty site (P < 0.05). These results suggest that granulocyte activation may be involved in restenosis after PTCA.

Adult↗
PubMed1996

Disappearance of coronary artery-ventricular fistulas after a radical operation for tetralogy of Fallot.

A 42-year-old Japanese man was diagnosed as tetralogy of Fallot (TOF). Coronary arteriography demonstrated coronary artery-ventricular fistulas (left coronary artery to left ventricle, right coronary artery to right ventricle). A radical operation for TOF was performed, including a patch closure of the ventricular septal defect, right ventricular muscle resection and a patch enlargement of the right ventricular outflow tract. After the operation, coronary arteriography showed a marked decrease in the shunt flow through the coronary artery-ventricular fistulas. Six months later, the patient was diagnosed as postoperative constrictive pericarditis, while the fistulas had almost completely disappeared. After pericardiectomy, when all hemodynamic variables were normal, the fistulas did not reappear. This is the first report of TOF complicated with multiple coronary artery-ventricular fistulas which completely disappeared after a radical operation. It is conceivable that in our case coronary artery-ventricular fistulas partially compensated for reduced arterial O2 saturation and disappeared after surgical correction with an improvement in hemodynamic variables.

Adult↗