S Iwamura

National Institute of Animal Health, Tsukuba, Ibaraki, Japan

Are you S Iwamura?

Claim your profile

Publications (18)32.12 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We validated a time-resolved fluoroimmunoassay (TR-FIA) using the lanthanide element europium as a non-radiological tracer for measuring luteinizing hormone (LH) in porcine peripheral blood. The dose-response curve of the reference standard ranged from 0.2048 to 50 ng/ml. Good parallelism was noted between the LH standard and plasma sample. The profile of LH throughout the estrous cycle, assessed by daily blood sampling, was consistent with the previous findings obtained by radioimmunoassays (RIAs). Moreover, the secretory patterns of pulsatile LH in the follicular phase and the preovulatory LH surge were also similar to those obtained in previous RIAs. We conclude that TR-FIA can be used to measure LH levels in porcine blood, with practical and convenient applications.
    Journal of Veterinary Medical Science 01/2008; 69(12):1291-4. · 0.88 Impact Factor
  • Source
    Chie Suzuki, Shokichi Iwamura, Koji Yoshioka
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, we attempted to produce piglets by non-surgically transferring blastocysts produced in vitro, using a flexible catheter as the transfer instrument. Cumulus-oocyte complexes (COCs) were aspirated from the follicles of ovaries obtained at a local slaughterhouse. They were then matured in modified North Carolina State University (NCSU)-37 medium for 44-46 h and fertilized in porcine gamete medium (PGM). Ten hours after in vitro fertilization (IVF), presumptive zygotes were removed from the cumulus cells and cultured in porcine zygote medium (PZM)-5. Blastocysts were cultured for five days after IVF and, using a catheter for deep intrauterine insemination without sedation, they were transcervically transferred into the uterine horn of six recipients (45-50 blastocysts/recipients) whose estrous cycles were synchronized, at 5 days after human chorionic gonadotropin (hCG) injection. Of the six recipients, one sow became pregnant and farrowed seven piglets (four live piglets) 119 days after hCG injection. The body weight at birth of the newborns ranged from 0.8 to 1.4 kg. These results indicate that it is possible to obtain piglets by transcervically transferring blastocysts produced by IVF and in vitro cultures in chemically defined media.
    Journal of Reproduction and Development 09/2004; 50(4):487-91. · 1.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To further develop defined conditions for in vitro fertilization (IVF) and in vitro culture (IVC) of in vitro-matured porcine oocytes, we evaluated the effects of theophylline, adenosine, and cysteine in a chemically defined medium during IVF. Viability to full term of in vitro-produced blastocysts after IVF and IVC in chemically defined medium was also investigated by embryo transfer to recipients. A chemically defined medium, porcine gamate medium (PGM), was modified from porcine zygote medium (PZM-4), which was previously established. PGM was used as a basal medium for IVF and PZM-4 was for the culture of presumptive zygotes. Addition of 2.5 mM theophylline to PGM significantly increased the percentage of male pronuclear formation compared with controls (no addition). Addition of 1 microM adenosine to PGM supplemented either with or without 2.5 mM theophylline significantly reduced the number of penetrated spermatozoa compared with controls (no addition of adenosine). Supplementation with 0.2 microM cysteine in PGM containing both 2.5 mM theophylline and 1 microM adenosine further increased the percentage of development to the blastocyst stage, compared with no supplementation of cysteine, but there was no difference in fertilization parameters, such as monospermy and pronuclear formation, regardless of presence or absence of theophylline and adenosine. When Day 5 blastocysts were transferred into four recipients (20-25 blastocysts per recipient), all recipients became pregnant and farrowed a total of 21 live piglets. The present results clearly demonstrate that porcine blastocysts can be produced by IVF and IVC in chemically defined media and that they can develop to full term after embryo transfer.
    Biology of Reproduction 01/2004; 69(6):2092-9. · 4.03 Impact Factor
  • C. Suzuki, K. Yoshioka, S. Iwamura
    Reproduction Fertility and Development 12/2003; 16(2):262-263. · 2.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of mono(2-ethylhexyl) phthalate (MEHP) on bovine oocyte maturation in vitro was examined. Cumulus-oocyte complexes (COCs) were cultured in maturation medium supplemented with various levels of MEHP for 24h, and then examined for the degree of cumulus expansion and the stage of maturation. A higher percentage of oocytes remained at the germinal vesicle (GV) stage after exposure to 75 and 100 micro M MEHP treatments (13.8 and 44.9% of oocytes, respectively) than the control (2.1% of oocytes). The proportion of oocytes that progressed to the metaphase II (MII) stage was significantly decreased with 25 micro M (59.6% of oocytes), 50 micro M (19.8%), 75 micro M (21.3%), and 100 micro M (3.1%) treatments than the control (77.3%). MEHP did not affect the process of cumulus expansion. For denuded oocytes, MEHP treatment of 50-100 micro M resulted in a significantly higher rate of oocytes remained at the GV stage compared to the control (53.4, 80.2, 88.4, and 5.4%, respectively). The rate of MII formation was significantly decreased with 10 micro M (60.9%) and 25 micro M (22.5%) MEHP treatments compared to control (68.9%). Furthermore, with 50, 75 or 100 micro M MEHP, no oocyte reached the MII stage. When COCs were cultured for 24h with 50 or 100 micro M MEHP and then cultured for an additional 24h in MEHP-free medium, most of the oocytes reached the MII stage (71.1 and 64.5%, respectively).Taken together, these results indicate that MEHP, at doses lower than those reported in blood transfusion patients, could negatively modulate bovine oocyte meiotic maturation in vitro, suggesting possible risks for human and other mammalians reproductive health.
    Reproductive Toxicology 01/2003; 17(3):305-10. · 3.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We evaluated the in vitro development of porcine zygotes that were cultured in a novel culture medium, porcine zygote medium (PZM), under different conditions and compared to in vivo development. The viability of these zygotes to full term after culture was also evaluated by embryo transfer to recipients. Porcine single-cell zygotes were collected from gilts on Day 2 after hCG injection. Culture of zygotes in PZM containing 3 mg/ml of BSA (PZM-3) produced better results in terms of proportion of Day 6 blastocysts, Day 8 hatching rate, and numbers of inner cell mass (ICM) cells and total cells in Day 8 embryos than that in North Carolina State University (NCSU)-23 medium. In culture with PZM-3, embryo development was optimized in an atmosphere of 5% CO2:5% O2:90% N2 compared to 5% CO2 in air. The ICM and total cell numbers in Day 6 embryos cultured in PZM-3 or in PZM-3 in which BSA was replaced with 3 mg/ml of polyvinyl alcohol (PZM-4) were also greater than those of NCSU-23 but less than those developed in vivo. However, no difference was found in the ratio of ICM to total cells among embryos developed in PZM-3, PZM-4, or in vivo. When the Day 6 embryos that developed in PZM-4 (99 embryos) or in vivo (100 embryos) were each transferred into six recipients, no difference was found in the farrowing rate (83.3% for both treatments) and in the number of piglets born (33 and 42 piglets, respectively). Our results indicate that porcine zygotes can develop into blastocysts in a chemically defined medium and to full term by transfer to recipients after culture.
    Biology of Reproduction 02/2002; 66(1):112-9. · 4.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of endotoxin on follicular growth and on secretion of LH, estradiol-17beta, progesterone and cortisol during the proestrous phase in cattle was investigated. Holstein heifers were treated with PGF2alpha at 11-13 d after ovulation to induce luteolysis. At 42 hr after PGF2alpha treatment, heifers were administered either lipopolysaccharide (LPS; Escherichia coli, O111:B4, 5 microg/kg, n = 6) or saline (control; n = 6) by i.v. bolus injection. Ovarian structures were monitored daily by transrectal ultrasonography, and blood samples were collected at various times for hormonal analysis. The duration from PGF2alpha treatment to ovulation was significantly longer in the LPS group (8.0 +/- 1.3 d) than in the control group (4.2 +/- 0.2 d). LPS significantly reduced the pulse frequency of LH for 6 hr after the administration, and increased the mean concentration and pulse amplitude of LH from 3 to 6 hr after the administration. The plasma concentrations of progesterone and cortisol were transiently increased after LPS administration. The plasma concentration of estradiol-17beta was significantly decreased at 24 hr after LPS administration compared to that in the controls. Five of six LPS-treated heifers exhibited no preovulatory LH surge until 120 hr after PGF2alpha treatment and the remaining heifer exhibited the surge at 108 hr after PGF2alpha treatment, while the LH surge was observed at 54-78 hr after PGF2alpha treatment in control heifers. These results suggest that endotoxin disrupts progression of the proestrous phase of cattle, interrupting the preovulatory estradiol rise and thus delaying the LH surge and the subsequent ovulation.
    Domestic Animal Endocrinology 06/2001; 20(4):267-78. · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The release profile of GnRH in cerebrospinal fluid (CSF) and its correlation with LH in peripheral blood of ovary-intact heifers during the estrous cycle were investigated. A silicon catheter was placed into the third ventricle of six heifers using ultrasonography. During the mid-luteal phase, the heifers were injected with prostaglandin F(2alpha) to induce luteolysis. Surges of CSF GnRH (66.7 h after prostaglandin F(2alpha) administration) and peripheral LH (66.3 h) occurred simultaneously and were coincident with the onset of estrus (67.0 h). Duration of elevated GnRH concentration considerably overlapped with the estrous phase in each of the heifers. Mean pulse frequencies of both GnRH and LH were significantly higher during the proestrous and early luteal phases than during the mid-luteal phase, while mean concentration and pulse amplitude of both GnRH and LH were not different between these three phases. Of all the GnRH pulses identified, more than 80% were accompanied by an LH pulse during the proestrous and early luteal phases. However, the proportion of GnRH pulses that were coincident with an LH pulse during the mid-luteal phase decreased to 60%. The results clearly demonstrate that a dynamic (pulse) and longer-term (surge) changes of GnRH release into CSF are physiologically expressed during the estrous cycle in heifers, and the pattern of pulsatile GnRH secretion in heifers depends upon their estrous cycle.
    Biology of Reproduction 03/2001; 64(2):563-70. · 4.03 Impact Factor
  • Source
    K Yoshioka, C Suzuki, S Iwamura
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of recombinant human activin A and follistatin on the developmental kinetics of bovine presumptive zygotes matured and fertilized in vitro using time-lapse cinematography were investigated. The presumptive zygotes were cultured for 9 days in a chemically defined medium (modified synthetic oviduct fluid, control) and modified synthetic oviduct fluid supplemented with activin A or follistatin. Development under cine-recording conditions was similar to that in an incubator. Addition of activin A to modified synthetic oviduct fluid increased, while addition of follistatin decreased, the percentage of zygotes that developed to morulae and blastocysts. Follistatin significantly prolonged the timing of development to the 9-16-cell stage compared with the control and activin A media. Activin A significantly shortened the duration of the third cell cycle compared with the control, but follistatin significantly prolonged the fourth cell cycle compared with the control and activin A. Developmental arrest ('lag-phase') during the 4-8-cell stage was observed in 95% of embryos developed to more than the 9-16-cell stage in all treatments. The greater the number of cells at the onset of the lag-phase, the earlier the onset of the phase and the shorter the duration of the phase, the further embryos were able to develop by day 9 in all treatments. The number of cells at the onset of the lag-phase in the medium containing activin A was significantly higher than it was in control or follistatin-containing media. Moreover, activin A significantly shortened the duration of the lag-phase compared with follistatin. The present results indicate that activin A may enhance in vitro development of bovine embryos by improving developmental kinetics, especially by increasing the number of cells at the onset of the lag-phase and shortening the duration of this phase.
    J Reprod Fertil 02/2000; 118(1):119-25.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A total of 29 SPF Large White prepuberal gilts (mean age 152 days at treatment) were examined for estrous and ovulatory responses after PG 600 treatment. After treatment, 85.2% of the gilts showed standing estrus within 6 days. Whereas the treatment-to-estrus interval and duration were 3.7 and 1.9 days respectively. As ovulation occurred on Day 5 to 6, appropriate timing of artificial insemination would be about 4 days after treatment. Fertility of gilts revealed to be excellent, giving rise to a high percentage of normal embryos, 85.3%. Meanwhile, development and growth of fetuses were mostly normal. Other reproductive performances recorded were: mean litter size 6.8; mean birth weight 1.26 kg; weaning-to-return estrus interval 5 to 8 days. In conclusion, PG 600 was found to be useful in inducing fertile estrus in prepuberal gilts, a result which will be of interest for commercial pig farms.
    Journal of Veterinary Medical Science 02/1999; 61(1):7-11. · 0.88 Impact Factor
  • K Yoshioka, C Suzuki, S Iwamura
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of activin A and/or follistatin on the development of bovine embryos were investigated. Presumptive zygotes matured and fertilized in vitro were cultured in a chemically defined medium (modified synthetic oviduct fluid medium; mSOF). Addition of 1-100 ng/ml of activin A to mSOF significantly increased the percentage of zygotes that developed to morulae and blastocysts (48-54% and 31-41%, respectively) compared with no addition (41% and 25%, respectively). In contrast, addition of 1-100 ng/ml follistatin significantly reduced the percentage of zygotes developing to morulae and blastocysts (29-31% and 17-20%, respectively) compared with no addition (41% and 28%, respectively). In a culture with 10 ng/ml of activin A, supplementation with the same concentration of follistatin neutralized the positive effect of activin A, while supplementation with 100 ng/ml of follistatin reduced the percentage of zygotes that developed. The total cell numbers in morulae and blastocysts were not affected by the addition of activin A and/or follistatin. The development-enhancing effects of activin A and the development-impeding effects of follistatin were observed when embryos were exposed to activin A or follistatin at a concentration of 10 ng/ml prior to the 9- to 16-cell stage. These results suggest that activin A and follistatin may affect bovine embryos until the third cell cycle and may play important roles in regulation of the developmental competence of bovine embryos.
    Biology of Reproduction 12/1998; 59(5):1017-22. · 4.03 Impact Factor
  • K Yoshioka, S Iwamura, H Kamomae
    [Show abstract] [Hide abstract]
    ABSTRACT: In a cow diagnosed as having ovarian cysts, we observed changes in the ovarian structures by ultrasonography for 71 days and examined plasma concentrations of sex hormones. The cow had 2 regressing cysts at the start of this study and 3 new follicles subsequently developed into cysts. With regression of these cysts, 2 new follicles developed and ovulated spontaneously, followed by the formation of 2 corpora lutea. On the day prior to ovulation, a preovulatory luteinizing hormone (LH) surge was detected. With regression of the corpora lutea, a new follicle developed and underwent atresia. Meantime, another follicle developed and became a cyst without ovulation. No preovulatory LH surge was observed during the period from regression of the corpora lutea to cyst formation. The results indicate that absence of the preovulatory LH surge is associated with occurrence of ovarian cysts and this endocrine aberration is reversible.
    Journal of Veterinary Medical Science 03/1998; 60(2):257-60. · 0.88 Impact Factor
  • Koji YOSHIOKA, Shokichi IWAMURA, Hideo KAMOMAE
    Journal of Veterinary Medical Science - J VET MED SCI. 01/1998; 60(2):257-260.
  • K Yoshioka, S Iwamura, H Kamomae
    [Show abstract] [Hide abstract]
    ABSTRACT: Changes in the diameters of individual follicular structures on ovaries were measured by transrectal ultrasonography for 29 to 40 days and the plasma concentrations of luteinising hormone (LH) follicle-stimulating hormone (FSH), progesterone and oestradiol-17 beta were determined in four cows with ovarian cysts. When these structures decreased in size, new follicular structures appeared and developed into cysts. Progesterone concentrations in plasma were below 1.0 ng ml-1 during the experimental periods. Plasma concentrations of oestradiol-17 beta fluctuated. The mean concentration of oestradiol-17 beta in plasma differed (P < 0.01) depending on the stage of the cyst. No preovulatory surges of LH were detected during the developmental stage of the cysts.
    Research in Veterinary Science 11/1996; 61(3):240-4. · 1.77 Impact Factor
  • K Yoshioka, S Iwamura, H Kamomae
    [Show abstract] [Hide abstract]
    ABSTRACT: To reliably detect early pregnancy factor (EPF) in cattle, monoclonal antibody specific for bovine CD2 molecule, which is the sheep red blood cell (SRBC) receptor on bovine T cell surface, was applied to the rosette inhibition test. The rosette inhibition titers (RITs) were significantly higher in pooled sera from early pregnant cattle than in those of non-pregnant cattle using two anti-bovine CD2 monoclonal antibodies, B26A4 (P < 0.001) and BAQ95A (P < 0.01). The dissociation value of RITs between pregnancy and non-pregnancy with B26A4 was greater than that with BAQ95A. The B26A4 monoclonal antibody was therefore applied to the rosette inhibition test in subsequent experiments. The RITs in serum of individual pregnant and non-pregnant cows 8 days after estrus were significantly different (P < 0.001) by three or more dilutions. When the rosette inhibition test was carried out in sera from individual pregnant and non-pregnant cows at estrus and at 24, 72 and 168 hr after ovulation, the RITs of pregnancy sera increased significantly at 24 hr after ovulation as compared with non-pregnancy sera (P < 0.001). These results indicate anti-bovine CD2 monoclonal antibody can be utilized with the rosette inhibition test to detect EPF in cattle, and that this assay detects bovine EPF for pregnancy serum at least 24 hr after ovulation.
    Journal of Veterinary Medical Science 09/1995; 57(4):721-5. · 0.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Clinical and endocrinological responses to administration of gonadotropin releasing hormone analog (LH-RH-A) during the lactation period and postweaning in the sow were investigated. Plasma LH concentrations in lactating sows rose immediately after administration of LH-RH-A. However, in postweaning sows the increase of LH level was more slowly. Three of 5 postweaning sows came into estrus and ovulated after LH-RH-A treatment. One sow exhibited a distinct LH response, but her ovaries remained quiescent. The remaining one with feeble estrus for a short period became cystic ovaries. Thus, LH response to GnRH in the sow seems to be higher during early lactation than at 2 days postweaning.
    Journal of Veterinary Medical Science 05/1991; 53(2):181-4. · 0.88 Impact Factor
  • Nippon juigaku zasshi. The Japanese journal of veterinary science 07/1989; 51(3):627-9.
  • Nippon juigaku zasshi. The Japanese journal of veterinary science 01/1989; 50(6):1222-31.