Biomedical subjects

N Koyama

Publications and source records attributed to N Koyama.

At least 19 recordsLinked to original sources

PubMed1992

Regulatory effects of platelet-derived growth factor-AA homodimer on migration of vascular smooth muscle cells.

Migration of medial smooth muscle cells (SMC) into the intima is important in intimal thickening of atherosclerotic tissues. To study the functions of three isoforms of platelet-derived growth factor (PDGF) in atherosclerosis, we investigated their effects on SMC migration by Boyden's chamber method. Although PDGF-AB and PDGF-BB enhanced SMC migration dose-dependently, PDGF-AA did not enhance SMC migration, but instead inhibited SMC migration induced by PDGF-AB or PDGF-BB. PDGF-AA also inhibited SMC migration induced by two other migration factors, fibronectin and SMC-derived migration factor. PDGF-AA is considered to be coexpressed with transforming growth factor (TGF)-beta 1 in atherosclerotic tissues. Treatment of SMC with TGF-beta 1 reduced an autocrine migration activity from SMC. Studies using anti-PDGF antibody revealed that an increased secretion of PDGF-AA by TGF-beta 1 caused the reduced migration activity. cAMP increase by forskolin and dibutyryl cAMP suppressed SMC migration, whereas cAMP decrease by pertussis toxin had no effects on PDGF-AA-suppressed migration. In contrast, staurosporine, an inhibitor of protein kinase C, enhanced SMC migration and neutralized the inhibitory effect of PDGF-AA. These findings suggest that PDGF-AA regulates SMC migration in intimal thickening in atheroma formation and that protein kinase C may play an important role in the inhibitory mechanism of PDGF-AA.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1992

Angiotensin II directly induces follicle rupture and oocyte maturation in the rabbit.

To investigate the possible direct involvement of angiotensin II (Ang II) in ovulation and oocyte maturation, Ang II at 100 or 10 micrograms was administered at 2-h intervals in the in-vitro perfused rabbit ovaries. The addition of Ang II in the perfusate induced ovulation in vitro in the absence of gonadotropin, while ovulation did not occur in any contralateral control ovaries. However, the ovulatory efficiency in the Ang II-treated ovaries was significantly lower than in hCG-treated ovaries. Ang II significantly stimulated the meiotic maturation of ovulated ova and follicular oocytes. Concomitant addition of the specific receptor antagonist of Ang II, saralasin, 30 min before the onset of Ang II administration blocked Ang II-induced ovulation in a complete manner. Although saralasin did not inhibit completely hCG-induced ovulation and oocyte maturation, these results suggest that Ang II produced in the ovary may act locally in the process of ovulation.

Angiotensin II↗

PubMed1992

A CHO strain producing high-level human IL-6 with the 3' deletion construct.

A Chinese Hamster Ovary (CHO) strain producing high-level human interleukin 6 (IL-6) was obtained, by introduction of the IL-6 cDNA from which the 3' AU-rich region was deleted. The IL-6 mRNA of this strain was stable. The productivity was more than 15 times higher than the previously obtained clone, which has intact IL-6 cDNA in the same expression vector. This strain produced IL-6 at a high level of 30 micrograms ml-1 in batch culture, or a continuous 20 micrograms per 10(6) cells per day in microcarrier cultivation.

Animals↗

PubMed1992

Direct effect of gonadotropin-releasing hormone agonists on the rabbit ovarian follicle.

OBJECTIVE: To determine if gonadotropin-releasing hormone agonist (GnRH-a)-induced oocyte maturation and degeneration can be attributed to the direct actions on the follicle. DESIGN: Mature rabbit follicle culture. INTERVENTIONS: The mature follicles were cultured with human chorionic gonadotropin (hCG) (100 ng/mL), buserelin acetate (10(-9) to 10(-6) M), leuprolide acetate (10(-9) to 10(-6) M), or buserelin acetate (10(-7) M) with a GnRH antagonist (10(-8) to 10(-6) M) for 14 hours. MAIN OUTCOME MEASURES: The percentage of oocytes achieving germinal vesicle breakdown, the oocyte degeneration rate, prostaglandins (PG) production by mature follicles, and the frequency of fertilization and embryonic development. RESULTS: Gonadotropin-releasing hormone agonist induced the meiotic maturation of follicle-enclosed oocytes in a dose-dependent manner while concomitantly increasing oocyte degeneration. The simultaneous addition of GnRH antagonist inhibited significantly GnRH-a-induced oocyte maturation and PG production by the mature follicles. Furthermore, a GnRH antagonist reversed the oocyte degeneration rate that had been increased by GnRH-a. The rates of normal fertilization and early embryonic development were significantly reduced in the oocytes matured by GnRH-a as compared with those matured by hCG. CONCLUSIONS: Gonadotropin-releasing hormone agonist acts directly on mature rabbit follicles to trigger the oocytes to undergo meiotic maturation, but oocytes matured in vitro by GnRH-a are not necessarily cytoplasmically mature.

Animals↗

PubMed1992

Effects of prolactin on ovarian plasmin generation in the process of ovulation.

The present study was undertaken to assess the effects of prolactin (PRL) on gonadotropin-induced plasmin generation in the in vitro-perfused rabbit ovary. The ovarian plasmin activity was determined by measuring plasmin bound to its major inhibitor, alpha 2-plasmin inhibitor (alpha 2 PI-Plm). In the first experiment, exposure to hCG enhanced ovarian alpha 2 PI-Plm generation from 1.2 +/- 0.3 ng/min/ovary in unstimulated ovaries to 2.9 +/- 0.3 ng within 2 h. The concentration of alpha 2 PI-Plm reached a maximum at 4 h and then declined. A second peak occurred 8 h after hCG administration; however, the ovarian alpha 2 PI-Plm generation without hCG was very low throughout the entire perfusion period. In the subsequent experiment, the addition of PRL(10-10(3) ng/ml) to the perfusate inhibited hCG-induced ovulation in a dose-dependent manner. Exposure to PRL at 10(3) ng/ml significantly (p less than 0.05) inhibited hCG-induced alpha 2 PI-Plm generation in ovaries throughout the entire perfusion period. Furthermore, PRL inhibited hCG-stimulated alpha 2 PI-Plm generation at 4 h after hCG administration in the perfused rabbit ovaries in a dose-dependent manner. In conclusion, PRL directly inhibits hCG-induced ovulation in rabbit ovary, at least in part, by a mechanism depending upon inhibition of the plasmin-generating system in the preovulatory follicles.

Animals↗

PubMed1992

Protein kinase C mediates gonadotropin-releasing hormone agonist-induced meiotic maturation of follicle-enclosed rabbit oocytes.

The present study was undertaken to determine the effects of a protein kinase C inhibitor, staurosporine, on gonadotropin-releasing hormone agonist (GnRHa)-induced oocyte maturation and follicular prostaglandin (PG) production, and the response to direct activators of protein kinase C using rabbit mature follicle culture. Treatment of mature follicles with GnRHa (buserelin and leuprolide acetate) neither stimulated nor inhibited cAMP accumulation in both the follicle and oocyte. Exposure to staurosporine at 10(-6) M 60 or 15 min before GnRHa (buserelin) administration reduced significantly the meiotic maturation of follicle-enclosed oocytes induced by GnRHa at 10(-7) M. However, staurosporine addition coincident with the agonist or thereafter did not inhibit meiotic maturation. Staurosporine suppressed GnRHa-induced meiotic maturation in a dose-dependent manner, whereas hCG-stimulated oocyte maturation was not inhibited. Similarly, staurosporine administered 60 min before exposure to GnRHa suppressed GnRHa-stimulated PG production by mature follicles. The active phorbol esters, 10(-6) M 12-0-tetra-decanoyl phorbol 13-acetate (TPA) and 10(-6) M 4 beta-phorbol 12,13-didecanoate (4 beta-PDD) stimulated meiotic maturation whereas the biological inactive isomer, 4 alpha-PDD, did not. The kinetics of germinal versicle breakdown of follicle-enclosed oocytes in the presence of active phorbol esters paralleled that of GnRHa-treated oocytes. Furthermore, the concomitant addition of staurosporine at 10(-6) M to the culture medium inhibited significantly (p less than 0.05) TPA-induced meiotic maturation. These data demonstrate that GnRHa stimulated both the meiotic maturation of follicle-enclosed oocytes and follicular PG formation via a mechanism other than the cAMP-mediated process.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗

PubMed1992

Human macrophages modulate the phenotype of cultured rabbit aortic smooth muscle cells through secretion of platelet-derived growth factor.

Phenotypic change of aortic smooth muscle cells (SMC) is a key step for their abnormal proliferation in atheromatous lesions. In this study modulation of the growth properties of SMC by macrophages was investigated to clarify the mechanism regulating the SMC phenotype. Cultured rabbit SMC preincubated with either macrophages derived from human peripheral monocytes, or conditioned medium from macrophages grew faster than control SMC in the absence of either macrophages or conditioned medium. SMC preincubated with purified platelet-derived growth factor (PDGF) also grew faster than control SMC in the absence of PDGF, and their rapid growth was maintained for at least two passages. SMC preincubated with conditioned medium of macrophages plus anti-PDGF antibody did not grow faster than control SMC. Furthermore SMC preincubated with PDGF acquired the ability to secrete some mitogen, which differed from PDGF. These results suggest that macrophages modulate the phenotype of SMC by a mechanism mediated by PDGF. As a result the SMC grow faster and at the same time secrete some mitogen probably distinct from PDGF in an autocrine manner.

Animals↗

PubMed1992

Pulmonary surfactant apoprotein-A in neonates with different respiratory disorders.

A serial determination of pulmonary surfactant apoprotein-A (SP-A) was made on tracheal aspirates from seven intubated infants with different types of respiratory failure in the first week of life. A two-site immunoassay with monoclonal antibodies was adopted to determine the SP-A concentration. The concentrations of albumin in the same samples were also assayed, and these data were expressed as the ratio of SP-A to albumin (SP-A/albumin ratio), and evaluated against clinical data such as the arterial-alveolar oxygen tension ratio (a/APO2) or ventilatory index. In infants with respiratory distress syndrome, the SP-A/albumin ratio was initially low, and increased gradually in the first few days of life with the improvement of a/APO2 and ventilatory index. The complication of pulmonary hemorrhage due to patent ductus arteriosus (PDA) resulted in a temporary decrease in the ratio. The infant with transient tachypnea of the newborn showed higher concentration from the first day of life and, in the course of PDA without pulmonary hemorrhage, the ratio did not decrease. The cases of congenital pneumonia showed the SP-A/albumin ratio remaining low while the infection was evident. These data suggest that the SP-A/albumin ratio of the tracheal aspirate can be used for the quantitative and qualitative evaluation of endogenous pulmonary surfactant in newborn infants with different respiratory disorders.

Albumins↗

PubMed1992

Inhibitory effect of ginsenosides on migration of arterial smooth muscle cells.

Migration of arterial smooth muscle cells (SMC) in the arterial wall plays an important role in the formation of intimal thickening of atherosclerotic lesions. In this study, we examined the effect of ginsenosides on SMC migration induced by platelet-derived growth factor (PDGF) and SMC-derived migration factor (SDMF). Ginsenosides had inhibitory effects on SMC migration and the striking effects were observed with ginsenoside-Rb2 and -Rc in a dose-dependent manner. These results suggest that the administration of ginsenosides on the patients may prevent intimal thickening, in part, by inhibiting SMC migration in the arterial wall.

Animals↗

PubMed1992

Possible involvement of lipoxygenase products in human corpora lutea.

The present study was undertaken to determine the ability of cultured luteal cells from human corpora lutea to secrete progesterone (P4) and prostaglandins (PGs), and to assess the effects of the products of the lipoxygenase pathway on luteal P4 production. Luteal cells responded to human chorionic gonadotropin (hCG) with a significant increase (2- to 7-fold) in P4 production. Arachidonic acid significantly stimulated PGE2 synthesis by luteal cells in a dose-dependent manner. Both basal PGE2 production and the responsiveness to arachidonic acid were maintained for 8 days. In contrast, both PGF2 alpha and 6-keto-PGF1 alpha production abruptly declined as the culture proceeded. However, the addition of hCG did not further stimulate the accumulation of the 3 PGs assayed. In the subsequent experiment, 5-hydroxyeicosatetraenoic acid (5-HETE) and the reaction products of soybean lipoxidase of arachidonic acid (AA-LIP) were utilized for evaluating the involvement of the lipoxygenase pathway in luteolysis. The addition of 5-HETE dose-dependently inhibited P4 production by the cultured luteal cells. Although treatment with either arachidonic acid or lipoxidase alone had no effect on P4 production, AA-LIP significantly reduced P4 production in the presence or absence of hCG. These results suggest that the products of the lipoxygenase as well as of the cyclo-oxygenase pathway may be important in regulating the life span and function of human corpora lutea.

Adult↗

PubMed1992

Stimulatory role of cyclic adenosine monophosphate as a mediator of meiotic resumption in rabbit oocytes.

The present study was undertaken to assess the role of alterations of intraoocyte cAMP concentrations in the meiotic maturation of isolated and follicle-enclosed oocytes. In isolated oocyte culture, the intracellular cAMP content of denuded oocytes declined within 15 min of incubation, whereas the cAMP content of cumulus-enclosed oocytes did not change substantially for 1.5 h of incubation, and then declined abruptly. Commitment to meiotic maturation was preceded by reduced concentrations of intraoocyte cAMP. Forskolin inhibited the spontaneous maturation of cumulus-enclosed oocytes in a dose-dependent manner. However, this inhibition was attenuated as the duration of incubation increased. Forskolin significantly stimulated the intracellular cAMP content of denuded and cumulus-enclosed oocytes, but intraoocyte cAMP returned to pretreatment values within 4 h. The decline in intraoocyte cAMP was followed by the meiotic maturation of isolated oocytes. In in vitro perfused rabbit ovaries, exposure to forskolin at 10(-4) M, as well as to 50 IU human CG, accelerated the meiotic maturation of follicle-enclosed oocytes. The intraoocyte cAMP content increased significantly within 30 min and reached its maximum 2 h following exposure to forskolin. Thereafter, cAMP decreased abruptly and returned to pretreatment levels by 6 h. These alterations of intraoocyte cAMP contents following exposure to forskolin paralleled those observed in human CG-treated ovaries. The decline in cAMP content of follicle-enclosed oocytes was followed by their meiotic maturation. In conclusion, the sustained elevation of intraoocyte cAMP levels inhibits the initiation of meiotic maturation in isolated and follicle-enclosed oocytes. Within the follicle, resumption of meiosis is triggered via a transient increase in intraoocyte cAMP, but commitment to meiosis must await the decline of intraoocyte cAMP.

Animals↗

PubMed1992

Possible involvement of leukotrienes in human luteal function.

The present study was undertaken to assess the ability of human corpora lutea to produce leukotriene B4 (LTB4). The maximum capacity of luteal cells to secrete progesterone was attained on day 4, and both the basal production and the responsiveness to hCG decreased thereafter. In contrast, the production of LTB4 by cultured luteal cells was significantly reduced on day 4, but increased thereafter. The basal concentration of LTB4 produced by luteal cells varied from 75 to 590 pg/10(5) cells/2 days. LTB4 production appeared to decrease concomitantly with increased-progesterone production in cultured luteal cells. Exposure to hCG decreased significantly LTB4 production by cultured luteal cells on day 4. An inhibitor of the lipoxygenase pathway, nordihydroguaiaretic acid (NDGA), inhibited LTB4 production in a dose-dependent manner. However, NDGA did not affect basal progesterone production by the cultured luteal cells. A significant inverse relationship existed between the accumulation rates of progesterone and LTB4 in the luteal cells. Furthermore, the addition of LTB4 inhibited progesterone production in a dose-dependent manner in both the presence and absence of hCG. In conclusion, LTB4 could be synthesized by human corpora lutea in vitro, and correlated inversely with the secretion rates of progesterone. These data suggest that LTB4 produced locally in the corpus luteum may be an important regulator in human luteal regression.

Adult↗

PubMed1992

Induction of meiotic maturation of follicle-enclosed oocytes of rabbits by a transient increase followed by an abrupt decrease in cyclic AMP concentration.

The involvement of cyclic adenosine monophosphate (cAMP) in mammalian oocyte maturation was assessed using cultures of rabbit cumulus-oocyte complexes and perfused rabbit ovaries. Rabbit cumulus-oocyte complexes were cultured in Brackett's medium with or without forskolin at 10(-4), 10(-5) or 10(-6) mol l-1 for 3-6 h. At 3 or 4 h spontaneous meiotic maturation was significantly (P < 0.05) inhibited by forskolin at 10(-4) mol l-1. With prolonged incubation, spontaneous maturation progressed despite exposure to forskolin. In the second experiment ovaries were perfused for 12 h with forskolin (10(-4), 10(-5) or 10(-6) mol l-1) or medium alone. Neither ovulation nor degeneration of follicular oocytes occurred in any perfused ovary. The percentage of follicular oocytes achieving germinal vesicle breakdown was significantly (P < 0.001) increased in response to forskolin in a dose-related manner. In an additional experiment, ovaries were perfused with forskolin at 10(-4) mol l-1. A significant increase in the cAMP content in the follicle was observed within 30 min, but the ability to produce cAMP in response to forskolin decreased as the duration of perfusion was increased. Intraoocyte cAMP increased significantly within 30 min and reached its maximum 2 h after exposure to forskolin. Thereafter, cAMP levels in the oocytes decreased abruptly. This drop in intraoocyte cAMP concentration was followed by the resumption of meiosis. The alterations of intraoocyte cAMP contents following exposure to hCG in vivo paralleled those observed in the ovaries perfused with forskolin. These data suggest that a transient, but not continuous, increase in cAMP concentration after the gonadotrophin surge may be required to initiate oocyte maturation.

Animals↗

PubMed1992

[An emergency coronary artery bypass for failed percutaneous transluminal coronary angioplasty with intractable ventricular tachycardia and fibrillation].

A 73-year-old man with effort angina after myocardial infarction is admitted for percutaneous transluminal coronary angioplasty (PTCA). During PTCA, the left anterior descending artery (LAD) was completely occluded. He was suffered from severe cardiogenic shock with systemic cyanosis and loss of consciousness. Under assist of intraaortic balloon pump (IABP) and cardiac massage, he was transferred to an operating room. Before the start of operation, cardioversion were required 13 times because of repeat attacks of ventricular tachycardia and fibrillation. Coronary artery bypass was completed in 177 minutes after total occlusion of the LAD. At the 5th postoperative day, IABP could be discontinued, and at the 8th postoperative day, the patient was weaned from mechanical ventilation. He was transferred to the prior hospital for rehabilitation on the 65 days after operation. We must try to perform CABG for salvage of myocardium, even if a patient falls in severe cardiogenic shock presenting intractable ventricular tachycardia and fibrillation.

Aged↗

PubMed1992

[Effects of tizanidine, a central muscle relaxant, upon spinal reflexes].

Effects of intravenous administration of tizanidine upon spinal reflexes were studied in cats anesthetized with urethane-chloralose. Both extensor and flexor monosynaptic reflexes and polysynaptic flexor reflex were inhibited by intravenous administration of tizanidine in a dose of 10-50 micrograms.kg-1. The inhibition was dose-dependent. After strychnine administration, polysynaptic flexor reflex was augmented, but the inhibition by tizanidine administration was unaffected. In spinal cats, inhibitory effect of tizanidine upon monosynaptic reflex was weaker than in intact cats. Viscero-intercostal reflex elicited by electrical stimulation of A delta afferent fibers in the greater splanchnic nerve was also inhibited by intravenous tizanidine (25 micrograms.kg-1). The degree of inhibition decreased in parallel with increase in the intensity of stimulus applied to the greater splanchnic nerve.

Animals↗

PubMed1991

A one step sandwich enzyme immunoassay for gamma-carboxylated osteocalcin using monoclonal antibodies.

A highly sensitive, simple and reliable one-step sandwich enzyme immunoassay (EIA) for the gamma-carboxylated form of osteocalcin (Gla-OC) has been developed using a monoclonal antibody. The minimum amount of Gla-OC detected by this EIA was approximately 0.2 ng/ml when a 10 microliter aliquot of the sample was used. The serum Gla-OC level in 30 healthy subjects was 3.6 +/- 2.19 ng/ml (mean +/- SD). A significant increase was seen in patients with chronic renal failure (20.3 +/- 4.60 ng/ml), atherosclerosis (8.3 +/- 4.94 ng/ml) and osteoporosis (10.1 +/- 4.60 ng/ml). The correlation between the values obtained by the sandwich EIA and competitive RIA methods was given by the linear regression equation, y = 2.896 + 0.759 chi, for which the correlation coefficient (r) was 0.815 (n = 58). This newly developed Gla-OC specific EIA may be useful for the diagnosis of metabolic bone disease and ectopic calcification.

Animals↗

PubMed1991

Transgenic mice expressing a B cell growth and differentiation factor gene (interleukin 5) develop eosinophilia and autoantibody production.

Interleukin 5 (IL-5) has been suggested to be involved in the growth and differentiation of B cells and eosinophils. Especially, Ly-1+ B cells, which have been considered to produce autoantibodies, are selectively developed by this lymphokine in long-term bone marrow culture. To envisage the possible engagement of IL-5 in the development of these cells in vivo, transgenic mice carrying the mouse IL-5 gene ligated with a metallothionein promoter were generated. Transgenic mice carrying the IL-5 gene exhibited elevated levels of IL-5 in the serum and an increase in the levels of serum IgM and IgA. A massive eosinophilia in peripheral blood, bone marrow, and spleen, and an infiltration of muscle and liver with eosinophils, were observed. When cadmium-containing saline was injected intraperitoneally into transgenic mice, IL-5 production was augmented about five times within 24 h, and a distinctive Ly-1+ B cell population became apparent in the spleen after 5 d. IL-5 receptors were detected on those cells by monoclonal antibodies against IL-5 receptors. Another interesting finding in these transgenic mice was an increase in polyreactive anti-DNA antibodies of IgM class. It is suggested, therefore, that aberrant expression of the IL-5 gene may induce accumulation of Ly-1+ B cells and eosinophils. Furthermore, this IL-5 transgenic mouse can be a model mouse for eosinophilia, and we can determine the role of IL-5 in the differentiation of Ly-1+ B cells and eosinophils by using this mouse.

Animals↗

PubMed1991

Polysaccharide-coated oil droplets in oil-in-water emulsions as targetable carriers for lipophilic drugs.

Surface of oil droplets in an oil-in-water (o/w) emulsion were coated with naturally occurring polysaccharides (such as mannan, amylopectin, and pullulan) which were, in part, bearing a cholesterol moiety. The mean size of the colloidal droplets was not altered much, even by coating with the polysaccharide derivatives, while the surface charge of the droplet decreased upon coating. Mannan and amylopectin derivative-coated droplets aggregated upon addition of Concanavalin A. These observations suggest that the terminal sugar moiety of the specific polysaccharides on the surface of colloidal droplets can be recognized by lectin. After intravenous injection of the emulsions into guinea pigs, kinetics of the blood clearance and the tissue distribution of the polysaccharide-coated oil droplets, which contain [14C]coenzyme Q10 as the marker, were investigated. In the initial rapid phase of blood clearance of the radioactivity, the polysaccharide-coated droplets were cleared from the blood stream slower than the uncoated ones. The lung uptake of the mannan derivative-coated droplet emulsion at 30 min after intravenous injection was approximately 15 times higher than that of the conventional emulsion without the polysaccharide coat.

Animals↗