Biomedical subjects

Nobuyoshi Imada

Publications and source records attributed to Nobuyoshi Imada.

7 recordsLinked to original sources

PubMed2004

Fertilization success and sexual behavior in male medaka, Oryzias latipes, exposed to tributyltin.

We evaluated the effects of tributyltin (TBT), polychlorinated biphenyls (PCBs), and a mixture of TBT and PCBs on reproduction, gonadal histology, and sexual behavior in Japanese medaka (Oryzias latipes). We administered TBT (1 microg g(-1) body weight [b.w.] daily), PCBs (1 microg g(-1) b.w. daily), or both to medaka for 3 weeks. We assessed reproductive success during week 3 and the sexual behavior of male medaka after the exposure period. Fertilization success was significantly decreased in groups that received TBT. The profiles of fertility developed a bimodal distribution in the TBT and TBT+PCBs groups, and the numbers of males that performed "following" and "dancing" were significantly decreased in the TBT+PCBs group. The frequency of "dancing" also decreased after treatment with TBT, whereas fish that received PCBs only showed no difference in sexual behavior. Testes that had oocytes showed normal spermatogenesis, even though two of the five males treated with TBT+PCBs had some indication of testis-ova, which did not occur in any other group. Our results indicate that TBT, but not PCBs, affects sexual behavior and reproduction in medaka.

Animals↗

PubMed2003

Suppression of sexual behavior in male Japanese medaka (Oryzias latipes) exposed to 17beta-estradiol.

Mating pairs of Japanese medaka (Oryzias latipes) received 17beta-estradiol (E2; dose, 3 and 30 microg/g body weight daily) in their diet and E2-free diet (control) for two weeks. The effect on reproductive success was assessed in the mating pairs, and sexual and nonsexual behaviors in the male were quantified. The fecundities of the E2-treated groups were reduced significantly (p < 0.05) compared with those of control, and the sexual behaviors (following, dancing, floating, and crossing) of male fish in response to prostaglandin F2alpha (PG)-injected E2-unexposed females were suppressed dramatically. While the fertility of spawned eggs and the frequencies of the nonsexual behaviors of resting and swimming in a straight line performed by male were unchanged in E2-exposed groups. Therefore, sexual behavior in male may be linked with reproductive success in mating pair of madaka exposed to E2. This assay for sexual behavior using PG may provide a useful tool for assessing the effect of endocrine-disrupting chemicals.

Animals↗

PubMed2003

Effects of 4-nonylphenol on reproduction of Japanese medaka, Oryzias latipes.

We exposed mature Japanese medaka (Oryzias latipes) to 4-nonylphenol (4-NP) to elucidate its reproductive effects and estrogenic responses. For each treatment, eight breeding pairs were exposed for 3 weeks at measured 4-NP concentrations of 24.8, 50.9, 101, and 184 micrograms/L. Egg production of the pairs during the third week of exposure (15-21 d) was significantly decreased in the > or = 101-microgram/L treatment group, and fertility was significantly decreased in the 184-microgram/L group. Induction of testis-ova was observed in male fish at all 4-NP concentrations, whereas abnormality of spermatogenesis was found only in those receiving the 184-microgram/L treatment. The gonadosomatic index of the males in the 184-microgram/L group was also remarkably reduced. Hepatic vitellogenin (VTG) levels were significantly increased in both sexes receiving 4-NP treatments of > or = 50.9 micrograms/L. Overall, the lowest-observed effective concentrations (LOECs) of 4-NP for decreasing reproductive capacity (fecundity and fertility) and eliciting estrogenic responses (induction of testis-ova and VTG) were 101 and < or = 24.8 micrograms/L, respectively. The LOEC for reduced reproduction in medaka was at least four-fold greater than that required to elicit estogenic responses in male fish. Thus, we suggest that the estrogenic responses expressed in male fish are not responsible for the reduction in reproductive capacity.

Animals↗

PubMed2003

Tributyltin causes masculinization in fish.

We examined the effect of tributyltin (TBT) on the sex differentiation process in genetically female Japanese flounder (Paralichthys olivaceus). The fish were fed an artificial diet containing tributyltin oxide (TBTO) at concentrations of 0.1 and 1.0 microg/g diet from 35 to 100 d after hatching, which includes the sex differentiation period. The ratio of sex-reversed males significantly increased to 25.7% of the flounder fed the 0.1 microg/g diet and to 31.1% of those fed the 1.0 microg/g diet compared with the control (2.2%). From morphological and histological examination of the fish in the TBT-treated groups, normal females had typical ovaries and sex-reversed males had typical testes. These results clearly demonstrated the masculinization of flounder exposed to TBTO. This is the first report of TBT inducing sex reversal in vertebrates.

Animals↗

PubMed2002

Effect of 17beta-estradiol on the reproduction of Japanese medaka (Oryzias latipes).

Estrogenic compounds such as 17beta-estradiol (E2) and its analogs are present in the aquatic environment and can adversely affect the reproductive systems of aquatic organisms. Although E2 has been detected at a maximum concentration of 64 ng/l in effluents of sewage treatment works (STWs), few reports address the associated effects on reproduction in fish. Therefore, we exposed adult medaka (Oryzias latipes) to mean measured E2 concentrations of 29.3, 55.7, 116, 227, and 463 ng/l for 21 d and assessed the effects on the egg number and fertility of paired medaka during the exposure period. In addition, we determined the hepatic vitellogenin (Vtg) concentration and histologically assessed the gonads of these fish. The number of egg produced and fertility of the paired medaka exposed to 463 ng/l E2 were significantly less compared with those of the control fish. Males in all treatment groups had developed testis-ova. Males treated with E2 concentrations = 55.7 ng/l contained relating great concentrations of hepatic Vtg. Therefore, although only the greatest E2 concentration tested in our study affected fecundity and fertility, effects of E2 were observed on induction of Vtg and testis-ova in male medaka exposed to environmentally relevant concentrations of E2.

Animals↗

PubMed2002

Purification and identification of a tributyltin-binding protein from serum of Japanese flounder, Paralichthys olivaceus.

Tributyltin (TBT) is an industrial chemical used as an antifoulant in marine environments. Previously, we reported that TBT accumulates in the serum or plasma of some fishes and is bound to a high molecular weight compound in the serum of the Japanese flounder, Paralichthys olivaceus. In this study, we succeeded in purifying the TBT-binding protein (TBT-bp) from the serum of Japanese flounder by using gel filtration chromatography, anion exchange chromatography, and polyacrylamide gel electrophoresis, with a 2.6% yield and a 77-fold purification. The molecular mass of TBT-bp was approximately 46.5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and its isoelectric point was approximately 3.0 on isoelectric focusing-polyacrylamide gel electrophoresis. The TBT-bp contained 42% N-glycan. The cDNA nucleotide sequence of TBT-bp was determined by reverse transcription-polymerase chain reaction of Japanese flounder liver, and we deduced a sequence of 191 amino acids of mature TBT-bp. No sequence identical to the TBT-bp amino acid sequence was found within the SWISS-PROT (http://www.nig. ac.jp/) protein database; however, a lipocalin-like sequence pattern was observed. We concluded that the TBT-bp was a novel protein that has not yet been reported, although some DNA sequences from expressed sequence tags (ESTs) of Japanese flounder liver had a high identity. A high expression level of TBT-bp gene was found in the liver, but the gene was slightly detectable in the kidney and brain.

Amino Acid Sequence↗

PubMed2002

Effects of bisphenol a on the reproduction of Japanese medaka (Oryzias latipes).

We elucidated the effects of bisphenol A (BPA) on the reproductive capacity (fecundity and fertility) and estrogenic response of adult Japanese medaka (Oryzias latipes) and studied the transgenerational effects (F, generation growth and sex) of this agent on the F1 offspring. Eight mating pairs of medaka were exposed to BPA for three weeks at a measured concentration of 837, 1,720, or 3,120 microg/L. Throughout the exposure period, we observed no reduction of fecundity and fertility in any treatment group and no reduction in survival and growth or any imbalance of the sex ratio of the offspring. However, histologic examination revealed testis-ova in 13% of the males in the 837-microg/L treatment group, 86% of those in the 1,720-microg/L group, and 50% of those that received 3,120 microg BPA/L. In addition, concentrations of hepatic vitellogenin were increased significantly in males treated with BPA at 3,120 microg/L (p = 0.0148). These results suggest that BPA is a weakly estrogenic compound that has the potential to alter sexual development and induce vitellogenin in male medaka but that has no adverse effect on reproductive success.

Animals↗