Biomedical subjects

Y Yoshimura

Publications and source records attributed to Y Yoshimura.

At least 19 recordsLinked to original sources

PubMed1992

Possible multifunction of glucose transporter. Transport of nicotinamide by reconstituted liposomes.

A kinetic study of the uptake of nicotinamide by reconstituted liposomes containing the human erythrocyte glucose transporter, compared with that of D-glucose, demonstrated that the Km and Vmax. values were almost the same for each compound, and that the uptake of D-glucose was competitively inhibited by nicotinamide. At 20 mM concentration, 2-deoxy-D-glucose, 3-O-methyl-D-glucose and 4,6-O-ethylidene-D-glucose all caused 50% inhibition of nicotinamide uptake, but L-glucose and nicotinic acid were not inhibitory. Similar results were obtained for the uptake of D-glucose. Cytochalasin B binding to the liposomes was inhibited in a dose-dependent manner by either nicotinamide or D-glucose. Antibody for glucose transporter detected in band 4.5 by SDS/PAGE inhibited the uptake of D-glucose and nicotinamide. A possible uptake of nicotinamide by nucleoside transporter was excluded. In human erythrocytes, cytochalasin B binding was inhibited dose-dependently by either nicotinamide or D-glucose, and cytochalasin B depressed the uptake of both nicotinamide and 2-deoxy-D-glucose. These findings were well reproduced in the reconstituted liposomes. The very close similarities between uptake of nicotinamide and D-glucose suggest that the glucose transporter plays a direct role in transport of nicotinamide, which is structurally quite different from monosaccharides, and thus that the transporter is probably multifunctional.

Biological Transport↗

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

Mutations in the Trp-Ser-X-Trp-Ser motif of the erythropoietin receptor abolish processing, ligand binding, and activation of the receptor.

The erythropoietin receptor (EPOR) is a member of the newly identified cytokine receptor superfamily. A common sequence motif, Trp-Ser-X-Trp-Ser (WSXWS), near the transmembrane domain is highly conserved in this family. To determine the function of this motif, we constructed deletion and insertion mutations in this part of the EPOR and introduced them into an interleukin-3 (IL-3)-dependent hematopoietic Ba/F3 cell line. Cells expressing the wild-type EPOR displayed 1,500 erythropoietin (EPO)-binding sites/cell with a single affinity of about 300 pM and proliferate in the presence of IL-3 or EPO. Ba/F3 cells expressing receptors mutated in the WSXWS motif displayed little EPO binding on the cell surface and did not grow in the presence of EPO. The mutant receptors were retained in the endoplasmic reticulum (ER) and, as such, were unable to bind EPO. A single Gly insertion between the two WS sequences caused defects in receptor structure and function similar to mutations lacking all or part of the WSXWS motif. The EPOR can be activated, resulting in proliferation independent of EPO either by an Arg129 to Cys point mutation or by association with the Friend spleen focus-forming virus (SFFV) envelope glycoprotein gp55. Introduction of the point mutation (Arg129 to Cys) did not activate any of the receptors mutated in the WSXWS motif. Moreover, gp55 did not activate the mutant receptors in Ba/F3 cells. Our study indicates that the WSXWS motif is critical for protein folding, ligand-binding, and signal transduction.

Amino Acid Sequence↗

PubMed1992

Homodimerization and constitutive activation of the erythropoietin receptor.

The erythropoietin receptor (EPO-R) is a member of the recently described cytokine receptor superfamily. A constitutively active (hormone independent) form of the EPO-R was isolated that has a single amino acid change in the exoplasmic domain, converting arginine-129 to cysteine (R129C). Since EPO-Rs containing R129S, R129E, and R129P mutations are functionally wild type, the presence of cysteine at residue 129, and not the loss of arginine, is required for constitutive activity. Several mutant forms of the EPO-R were analyzed; all constitutively active mutants form disulfide-linked homodimers, whereas EPO-responsive or inactive forms of the receptor do not. Monomers and disulfide-linked dimers of the constitutive receptor are present on the plasma membrane and bind EPO with a single affinity. Homodimerization of the EPO-R is likely to play a role in ligand-induced signal transduction, and disulfide-linked dimerization of the constitutive receptor may mimic this step.

Animals↗

PubMed1992

Interaction of bovine serum albumin with the surface of a microcrystalline aluminum oxide hydroxide compound: a possible new type of phosphate adsorbent.

Aluminum hydroxide gel (ALG) has been effective for ameliorating acidosis associated with phosphatemia caused by hemodialysis. However, aluminum accumulation in the body causes severe side effects. As substitute for ALG, a new type of aluminum oxide hydroxide (tentatively named PT-A) was prepared with the hope of future clinical use. PT-A has a microcrystalline structure with a high resistance to pH change and has more phosphate-binding efficacy than ALG. It was tested for possible interaction with protein by adsorption test, zeta-potential analysis, X-ray diffraction, and scanning electron microscopy. Bovine serum albumin (BSA) was chosen as a model protein. The interaction of BSA with PT-A depended on the amount of adsorbent. Protein adsorption occurred rapidly and reached the maximal level at near neutral pHs. Phosphate adsorption was not affected by the presence of BSA, but the interaction of BSA with PT-A was significantly reduced by the presence of phosphate. Zeta-potential changes on the surface of PT-A indicated that the positively charged surface of PT-A was covered with negatively charged phosphate ions that repelled negatively charged BSA molecules. X-ray diffraction patterns indicated no observable structural alteration caused by adsorption of BSA or phosphate, and scanning electron microscopy revealed that BSA covered the outer surface of PT-A but did not cover small pores, where phosphate can freely penetrate.

Adsorption↗

PubMed1992

Changes in protein kinase C activity in rat calvarial bone cells cultured in a low-calcium environment.

This enzyme activity was examined in bone cells cultured for 8-10 days; the calcium concentration was 1.87 +/- 0.05 (n = 10) mM in the control medium and 0.34 +/- 0.02 (n = 10) mM in the low-calcium medium. The activity was significantly lower in the low-calcium group than in the control (p less than 0.01). The cytosolic fraction decreased more than the membranous fraction. After restoration to a regular calcium environment, the protein kinase C activity recovered rapidly to near the control value. The extent of recovery was greater in the membranous than in the cytosolic fraction. These results suggest that the enzyme was inhibited in bone cells placed in a low-calcium environment, while the sensitivity in the membrane was enhanced.

Animals↗

PubMed1992

Prototype of a reflux-preventing ureteral stent and its clinical use.

We have experimentally produced a ureteral stent which prevents vesicorenal reflux. This stent has a thin silicon sleeve at its distal end (intravesical portion). In a model experiment the sleeve demonstrated an excellent capability to prevent reflux. The sleeve allowed flow of fluid with minimal pressure rise. A patient with bilateral ureteral obstruction was managed with endoscopic insertion of a sleeved stent in the right ureter and a usual pigtail stent in left ureter. During cystography vesicorenal reflux was not observed on the right side while reflux occurred on the left side. Excretory urography forty days after stent placement demonstrated recovery of renal function and maintenance of drainage in both renal units. Thus, the drainage characteristic of this stent appears to be approximately the same as that of usual stent.

Drainage↗

PubMed1992

Tongue cancer treated with irradiation: assessment with MR imaging.

We examined the usefulness of MRI in differentiating post-radiation scar tissue from the residual tumour. Ten consecutive patients who underwent MR imaging before and after radiation therapy were assessed prospectively. T1- and T2-weighted images using a 1.5 unit were obtained in 10 patients (3 T1, 6 T2, 1 T3) at 1 week before irradiation, and 2 weeks, 2 months, 4 months, 6 months and every 6 months thereafter following completion of radiation. Although all T2 and T3 tumours demonstrated high signal intensity compared to muscle on T2-weighted images, the T1 tumour could be demonstrated in only one of three patients. Six patients in whom the primary tumour clinically disappeared demonstrated low signal intensity on T2-weighted images until 4 months after completion of radiation therapy (range 1 week to 4 months). This study suggests that MRI can detect primary tumours larger than T2 (2 cm), and may be useful in assessing the effectiveness of therapy for tongue cancer.

Adult↗

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

Long-term depression is induced in Ca2+/calmodulin kinase-inhibited visual cortex neurons.

To elucidate a role of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in induction of long-term potentiation (LTP), KN-62, a selective inhibitor for CaMKII, was injected into layer 2/3 neurons of sliced visual cortex obtained from young rats. Tetanic stimulation (5 Hz, 1 min) applied to the white matter after the KN-62 injection induced long-term depression (LTD) of excitatory postsynaptic potentials (EPSPs) evoked by test stimulation of the white matter in 9 of the 14 cells tested. However, EPSPs evoked by test stimulation of the non-tetanized site were not changed, indicating that the induction of LTD was input-specific. Simultaneously, recorded field potentials which were derived from neurons with intact CaMKII showed LTP. These results suggest that postsynaptic CaMKII plays a role in the induction of LTP/LTD in visual cortex.

Animals↗

PubMed1992

Effect of antacid on absorption of the quinolone lomefloxacin.

The effect of antacid on the absorption of lomefloxacin (LFLX) in humans was studied. When LFLX was orally administered concomitantly with aluminum- and magnesium-containing antacids under fasting conditions, its level in plasma decreased by one-half and its area under the concentration-time curve was reduced by 40% compared with the levels observed after treatment with LFLX alone. The urinary recovery value also decreased by 40%. No such effects were noted after coadministration of LFLX and a nonmetallic antacid. This study confirmed the existence of chelate complexes of LFLX with Al3+ and Mg2+ and examined the chelating strength. The stability constants of LFLX with Al3+ and Mg2+ were measured and compared with those of ofloxacin and norfloxacin; little difference was observed among them. LFLX was found to bind more strongly with Al3+ than with Mg2+. Further, the existence of chelate formation was proven by 13C-nuclear magnetic resonance spectroscopy. The decrease in the LFLX level in plasma in humans could be explained by a reduced absorption of the Al(3+)- and Mg(2+)-LFLX chelate complexes.

Adult↗

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

Role of corpus luteum function in embryo implantation.

The present study was undertaken to evaluate the role of corpus luteum function in the implantation process of cryopreserved embryos. Six patients with tubal infertility were studied, with a total of 27 fresh embryos being replaced following controlled ovarian hyperstimulation and in vitro fertilization. These embryo transfers failed to produce pregnancy. From the patients, 22 supernumerary embryos were cryopreserved and 10 viable frozen-thawed embryos were transferred in a subsequent natural cycle, resulting in 2 pregnancies. In 1 of the pregnancies, the serum concentrations of estradiol (E2) and progesterone (P4) in the midluteal phase were 29 pg/ml and 5.6 ng/ml, respectively. These values were considered to be below the physiological range. These data suggest that a pregnancy can be achieved in spite of low circulating E2 and P4 levels during the luteal phase, which are generally indicative of the luteal phase defect.

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

Characterization of thyroidal membrane-bound Mg-adenosinetriphosphatase activated by trypsin or poly-L-lysine.

The Mg-adenosinetriphosphatase (ATPase) in the thyroidal NaI-treated microsome fraction was activated by treatment with basic polyamino acids or trypsin, but not with acidic polyamino acids and basic proteins such as lysozyme and ribonuclease. The enzyme kinetics showed that the activation of trypsin or poly-L-lysine was due to an increase in the maximal velocity of the hydrolyzing reaction without a change in the affinity of the enzyme for its substrate. A break at about 25 degrees C was observed in the Arrhenius plots of Mg-ATPase in the trypsin- or poly-L-lysine treated preparations, but there was no break in the control preparation. These results suggest that the activating effect of trypsin or poly-L-lysine on Mg-ATPase activity in the thyroidal NaI-treated microsome fraction is related to the lipid environment surrounding the enzyme molecule in the thyroid cell membrane.

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↗