Masaki Nagae

The effect of cortisol administration on blood plasma immunoglobulin M (IgM) concentrations in masu salmon (Oncorhynchus masou)

Immunoglobulin M (IgM) is known as a main factor in the humoral immune system of teleosts. In the present study, the effect of cortisol on plasma IgM concentrations was investigated using a specific antibody to IgM in masu salmon (Oncorhynchus masou). Cortisol was orally administered each day for 2 weeks at a dose of 1 mg g−1 in the diet, and for the following week the fish were fed a non-treated diet. Blood plasma samples were collected at 0, 1, 2 and 3 weeks after the initiation of treatment. Oral administration of cortisol elevated plasma cortisol concentrations to about 40 ng/ml for 2 weeks after administration and slightly reduced plasma IgM concentration; the suppression was statistically significant one week after the period of hormone administration. However, treatment with cortisol did not affect plasma concentrations of total protein or α1-protein, one of the major serum proteins, during the experimental period. These results indicate that cortisol specifically suppresses plasma IgM concentrations.

Changes in serum immunoglobulin M (IgM) concentrations during early development of chum salmon (Oncorhynchus keta) as determined by sensitive elisa technique

1. n1. A specific and sensitive sandwich enzyme-linked immunosorbent assay (ELISA) was developed for the measurement of low levels of serum immunoglobulin M (IgM) of chum salmon Oncorhynchus keta. n n2. n2. In this assay, 5 μl serum was enough to measure the concentration of IgM and the minimum detectable concentration of serum IgM was about 5 ng/ml. n n3. n3. Coefficients of variation within and between assays ranged from 2.90 to 9.61%. n n4. n4. IgM concentrations remained at low level (< 300 ng/ml) until 40 days after hatching and then increased rapidly at the period of emergence (48 days after hatching).

Changes in transcription of pituitary glycoprotein hormone α and gonadotropin IIβ subunits during ovarian development induced by repeated injections of salmon pituitary homogenate in the Japanese eel, Anguilla japonica

To investigate transcription of pituitary glycoprotein hormone a and gonadotropin IIβ (GTH IIβ) subunits in female Japanese eel, gene quantitation systems using reverse transcription-polymerase chain reaction (RT-PCR) were developed, using β-actin as an internal control gene. These systems were not only sensitive, but also precise, with low coefficients of variation within and between assays (below 20 and 30%, respectively). Using these quantitation systems, we investigated how transcription of both subunits changed in Japanese eel during ovarian development induced by repeated injections of salmon pituitary homogenate (SPH). Transcriptional level of pituitary glycoprotein hormone α was similar to that of ß-actin before SPH injection, and increased slowly during ovarian development, reaching a maximum (3-fold increase over initial levels) at the migratory nucleus stage. In contrast, the level of GTH IIβ mRNA was very low (about one-tenth that of β-actin) before SPH injection, but expression increased markedly during ovarian development with an approximate 120-fold increase over initial levels (12 times that of β-actin) at the migratory nucleus stage. These results suggest that GTH II synthesis in female eel was activated during ovarian development induced by repeated SPH injections. The increase in mRNA levels of both subunits mRNA is probably due to sex steroids produced in eel ovarian follicles. Unexpectedly, transcriptional level of GTH IIβ was abnormally high compared to that of pituitary glycoprotein hormone α at the migratory nucleus stage. These results suggest that repeated SPH injections induced aberrant endocrine conditions in female Japanese eels.

Effects of thyroid hormone on gonadotropin-induced steroid production in medaka, Oryzias latipes, ovarian follicles.

RésuméDes prélèvements sanguins et ovariens ont été effectués toutes les 4 heures avant la ponte chez des médakas (Oryzias latipes) synchronisés par la photopériode (14 L-10N). Les niveaux plasmatiques en oestradiol-17β (E2) sélèvent rapidement 16h avant la ponte et présentent un pic 8h avant celle-ci. Des ovocytes inclus dans leur follicule (follicules ovariens) à différents stades de développement ont été isolés et utilisés pour étudier in vitro leffet dhormone thyroïenne (triiodothyronine, T3) sur la production dE2 induite par la gonadotropine (GTH) provenant de sérum de jument gravide. La GTH à une concentration de 100 UI/ml stimule la production dE2 par des follicules ovariens collectés entre 32 et 16h avant la ponte. Trente et deux heures avant la ponte, la T3 (5ng/ml) administrée en même temps que la GTH (100 UI/ml) a entraîné une augmentation de 3.5 fois de la production dE2 par rapport au traitement GTH seul. Ces résultats suggèrent que, chez la médaka, la T3 peut agir directement au niveau des follicules ovariens pour modifier la production dE2 stimulée par la GTH.AbstractBlood and ovarian samples were collected at intervals of 4h prior to spawning time from medaka (Oryzias latipes) that were maturationally synchronized with artificial photoperiod (14h light: 10h dark). Plasma estradiol-17β (E2) levels increased rapidly from 16h before spawning and peaked at 8h before spawning. Follicle-enclosed oocytes (ovarian follicles) at different stages of development were isolated from the ovaries and used to study the in vitro effects of thyroid hormone (triiodothyronine; T3) on pregnant mare serum gonadotropin (GTH)-induced E2 production. GTH at a concentration of 100 IU/ml stimulated E2 production by ovarian follicles collected between 32 and 16h before spawning. At 32h before spawning, T3 (5 ng/ml) administered along with GTH (100 IU/ml) resulted in a 3.5 fold increase in E2 production, compared with GTH administered alone. These results suggest that T3 can act on ovarian follicles directly to modulate GTH-stimulated E2 production in the medaka.